在只有一个元素的 RecyclerView 中将 CardView 居中
Center a CardView in a RecyclerView with only one element
我使用的是 RecyclerView，其中包含带有 TextView 和 ImageView 的 CardView（每张卡片代表一个城市）。我还在每张卡片上都有一个 onClickListener，它会引导我进入城市中的博物馆列表。 （RecyclerView 由 ArrayList 填充）。
列表是由同一个垂直滚动的Cardview组成的RecyclerView
当一个城市只有一个博物馆时，如何在屏幕中央显示唯一的CardView？
这是activity xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.bebbo203.mymuseum.MuseumActivity">
<android.support.v7.widget.RecyclerView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/recyclerViewMuseum"
android:scrollbars="vertical"
android:scrollIndicators="none"
android:gravity="center_horizontal"
/>
</RelativeLayout>
这是 RecyclerView xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:baselineAligned="false"
xmlns:card_view="http://schemas.android.com/apk/res-auto">
<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="150dp"
android:id="@+id/cardView"
card_view:cardCornerRadius="2dp"
card_view:cardUseCompatPadding="true"
android:gravity="center_horizontal"
android:animateLayoutChanges="true"
>
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:layout_width="match_parent"
android:layout_height="150dp"
android:id="@+id/imageViewList"
android:layout_gravity="center_horizontal|top"
android:adjustViewBounds="true"
android:scaleType="centerCrop"/>
<TextView
android:id="@+id/textViewList"
android:layout_width="match_parent"
android:layout_height="150dp"
android:textSize="40sp"
android:textIsSelectable="false"
android:textAlignment="center"
android:gravity="fill"
android:textStyle="bold"
android:layout_weight="1"
android:layout_gravity="center_horizontal|top"/>
</FrameLayout>
</android.support.v7.widget.CardView>
</RelativeLayout>`
感谢您的帮助。
这就是 MainActivity。城市列表。这里一切都很好。
当我点击只有一个博物馆的 Parigi 时，我想在屏幕中央显示单个卡片视图
（如果可能的话，我想让卡片视图从屏幕中央开始，而不是从顶部开始。就像当我打开 activity 时中央卡片视图始终位于中央一样。例如在中心翻译 NationalGallery 维护其他的顺序)
1.Try 当 recyclerview 有 1 个子视图时设置 LayoutParams CENTER_IN_PARENT
2.Or 使用 FrameLayout 作为 recyclerView 的父级并设置 layout_gravity
3.Or 只需计算 cardview 上方的 space 并将 marginTop 设置为 recyclerView 或将 setTranslationY 设置为 recyclerView
4.Or 在 Recylerview.
添加一个 itemDecaration，高度为 space'
RelativeLayout.LayoutParams rLp = (RelativeLayout.LayoutParams) recyclerView.getLayoutParams();
if(data != null || data.size()>1){
rLp.removeRule(RelativeLayout.CENTER_IN_PARENT);
}else{
rLp.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);
}
recyclerView.setLayoutParams(rLp);
当recyclerView只有一个child时使用这个LayoutManager:
import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
public class FullyLinearLayoutManager extends LinearLayoutManager {
private static final String TAG = FullyLinearLayoutManager.class.getSimpleName();
private MeasureEndListener mMeasureEndListener;
public FullyLinearLayoutManager(Context context) {
super(context);
}
private float divHeight =0;
public FullyLinearLayoutManager(Context context,float height) {
super(context);
divHeight = height;
}
public FullyLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
private int[] mMeasuredDimension = new int[2];
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
Log.i(TAG, "onMeasure called. \nwidthMode " + widthMode
+ " \nheightMode " + heightSpec
+ " \nwidthSize " + widthSize
+ " \nheightSize " + heightSize
+ " \ngetItemCount() " + getItemCount());
int width = 0;
int height = 0;
for (int i = 0; i < getItemCount(); i++) {
measureScrapChild(recycler, i,
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
mMeasuredDimension);
if (getOrientation() == HORIZONTAL) {
width = width + mMeasuredDimension[0];
if (i == 0) {
height = mMeasuredDimension[1];
}
} else {
// LogUtils.e(mMeasuredDimension[1]);
height = height + mMeasuredDimension[1];
if(i!= getItemCount()-1){
height += divHeight;
// LogUtils.e(divHeight + "xxx add"+DensityUtils.dp2px(divHeight));
}else{
height += 2*divHeight;
// LogUtils.e(divHeight+ "xxx no add"+ DensityUtils.dp2px(divHeight));
}
if (i == 0) {
width = mMeasuredDimension[0];
}
}
}
switch (widthMode) {
case View.MeasureSpec.EXACTLY:
width = widthSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
switch (heightMode) {
case View.MeasureSpec.EXACTLY:
height = heightSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
if(mMeasureEndListener!=null){
mMeasureEndListener.onMeasureEnd(width,height);
// new Thread().interrupt();
}
setMeasuredDimension(width, height);
}
private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
int heightSpec, int[] measuredDimension) {
try {
View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException
if (view != null) {
RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
getPaddingLeft() + getPaddingRight(), p.width);
int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
getPaddingTop() + getPaddingBottom(), p.height);
view.measure(childWidthSpec, childHeightSpec);
measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
recycler.recycleView(view);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
}
}
public interface MeasureEndListener{
void onMeasureEnd(int width,int height);
}
public void setMeasureEndListener(MeasureEndListener mMeasureEndListener){
this.mMeasureEndListener = mMeasureEndListener;
}
}
当只有一项或多项时，尝试将高度设置为 RecyclerView。
请参阅 this topic 以执行此操作。当只有一项时，将 RecyclerView 设置为 WRAP_CONTENT。当有更多一项时，将 RecyclerView 设置为 MATCH_CONTENT。祝你好运！
我已经实现了简单的 HelloWorld 应用程序，它显示了城市列表并根据它拥有的博物馆数量显示了全尺寸城市名片或它的居中包装版本。
（是的，我不太擅长艺术:-)）
这是我的做法。
长话短说：
关键是ItemDecoration：设置合适的项目偏移量，你会得到你需要的;这是我的做法：
RecyclerView recyclerViewMuseum = (RecyclerView)findViewById(R.id.recyclerViewMuseum);
recyclerViewMuseum.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
recyclerViewMuseum.setAdapter(adapter);
recyclerViewMuseum.addItemDecoration(new RecyclerView.ItemDecoration() {
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
if (view instanceof CityWithOneMuseumCardView) {
int totalWidth = parent.getWidth();
int cardWidth = getResources().getDimensionPixelOffset(R.dimen.small_card_width);
int sidePadding = (totalWidth - cardWidth) / 2;
sidePadding = Math.max(0, sidePadding);
outRect.set(sidePadding, 0, sidePadding, 0);
}
}
});
这是我的模型 - City 和 Museum 类:
public class Museum {
public String title;
public Museum(String title) {
this.title = title;
}
}
public class City {
public String title;
public int imageRes;
public List<Museum> museums = new ArrayList<>();
public City(String title, int imageRes) {
this.title = title;
this.imageRes = imageRes;
}
}
然后是浏览量：CityWithManyMuseumsCardView 和 CityWithOneMuseumCardView。他们都在使用辅助接口 IItemDisplayer.
public class CityWithOneMuseumCardView extends CardView implements IItemDisplayer<City> {
public CityWithOneMuseumCardView(Context context) {
super(context);
LayoutInflater.from(context).inflate(R.layout.one_museum_layout, this);
}
@Override
public void displayItem(City city) {
TextView cityTitleTextView = (TextView)findViewById(R.id.cityTitleTextView);
cityTitleTextView.setText(city.title);
}
}
public class CityWithManyMuseumsCardView extends CardView implements IItemDisplayer<City> {
public CityWithManyMuseumsCardView(Context context) {
super(context);
LayoutInflater.from(context).inflate(R.layout.many_museums_layout, this);
}
@Override
public void displayItem(City city) {
ImageView cityBackgroundImageView = (ImageView)findViewById(R.id.cityBackgroundImageView);
cityBackgroundImageView.setImageResource(city.imageRes);
TextView cityTitleTextView = (TextView)findViewById(R.id.cityTitleTextView);
cityTitleTextView.setText(city.title);
TextView cityNumberOrMuseumsTextView = (TextView)findViewById(R.id.cityNumberOrMuseumsTextView);
cityNumberOrMuseumsTextView.setText(String.valueOf(city.museums.size()));
}
}
public interface IItemDisplayer<TItem> {
public void displayItem(TItem item);
}
以及他们的布局：
<!-- One Museum card -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:background="#BB2050AB"
android:layout_width="@dimen/small_card_width"
android:layout_height="200dp">
<TextView
android:background="#AA000000"
android:textColor="#FFFFFF"
android:text="Only one museum available"
android:textSize="16sp"
android:padding="4dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/cityTitleTextView"
android:layout_gravity="bottom"
android:background="#AAFFFFFF"
android:textColor="#000000"
android:textSize="24sp"
android:paddingStart="16dp"
android:paddingEnd="16dp"
android:gravity="center"
android:layout_width="match_parent"
android:layout_height="48dp" />
</FrameLayout>
<!-- Many museums card -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="240dp">
<ImageView
android:id="@+id/cityBackgroundImageView"
android:scaleType="fitXY"
android:layout_width="500dp"
android:layout_height="match_parent" />
<TextView
android:id="@+id/cityNumberOrMuseumsTextView"
android:layout_gravity="top|end"
android:background="#AA000000"
android:textColor="#FFFFFF"
android:textSize="16sp"
android:padding="4dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/cityTitleTextView"
android:layout_gravity="bottom"
android:background="#AA000000"
android:textColor="#FFFFFF"
android:textSize="24sp"
android:paddingStart="16dp"
android:paddingEnd="16dp"
android:gravity="center_vertical"
android:layout_width="match_parent"
android:layout_height="48dp" />
</FrameLayout>
然后我们需要为我们的 RecyclerView 创建一个适配器
CityAdapter.java
public class CityAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
final static int ITEM_TYPE_MANY_MUSEUMS = 0;
final static int ITEM_TYPE_ONE_MUSEUM = 1;
private List<City> items;
public CityAdapter(List<City> items) {
this.items = items;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
switch (viewType) {
case ITEM_TYPE_MANY_MUSEUMS:
return new ViewHolder(new CityWithManyMuseumsCardView(viewGroup.getContext()));
case ITEM_TYPE_ONE_MUSEUM:
return new ViewHolder(new CityWithOneMuseumCardView(viewGroup.getContext()));
default:
throw new IllegalArgumentException(String.format("Unexpected viewType: %d", viewType));
}
}
@Override
public int getItemViewType(int position) {
if (items == null || items.size() < position) {
throw new IllegalArgumentException("Wrong position!");
}
if (items.get(position).museums.size() > 1) {
return ITEM_TYPE_MANY_MUSEUMS;
} else if (items.get(position).museums.size() == 1){
return ITEM_TYPE_ONE_MUSEUM;
}
throw new IllegalArgumentException("Wrong number of museums!");
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
((IItemDisplayer<City>) holder.itemView).displayItem(items.get(position));
}
@Override
public int getItemCount() {
return items.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
public ViewHolder(View itemView) {
super(itemView);
}
}
}
我已将此项目上传到我的保管箱 - 欢迎 check it out！希望对你有帮助。
你能试试这个吗:
import android.content.Context;
import android.graphics.Rect;
import android.support.v4.view.ViewCompat;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import java.lang.reflect.Field;
/**
* {@link android.support.v7.widget.LinearLayoutManager} which wraps its content. Note that this class will always
* wrap the content regardless of {@link android.support.v7.widget.RecyclerView} layout parameters.
* <p/>
* Now it's impossible to run add/remove animations with child views which have arbitrary dimensions (height for
* VERTICAL orientation and width for HORIZONTAL). However if child views have fixed dimensions
* {@link #setChildSize(int)} method might be used to let the layout manager know how big they are going to be.
* If animations are not used at all then a normal measuring procedure will run and child views will be measured during
* the measure pass.
*/
public class WrapContentLinearLayoutManager extends android.support.v7.widget.LinearLayoutManager {
private static boolean canMakeInsetsDirty = true;
private static Field insetsDirtyField = null;
private static final int CHILD_WIDTH = 0;
private static final int CHILD_HEIGHT = 1;
private static final int DEFAULT_CHILD_SIZE = 100;
private final int[] childDimensions = new int[2];
private final RecyclerView view;
private int childSize = DEFAULT_CHILD_SIZE;
private boolean hasChildSize;
private int overScrollMode = ViewCompat.OVER_SCROLL_ALWAYS;
private final Rect tmpRect = new Rect();
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(Context context) {
super(context);
this.view = null;
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
this.view = null;
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(RecyclerView view) {
super(view.getContext());
this.view = view;
this.overScrollMode = ViewCompat.getOverScrollMode(view);
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(RecyclerView view, int orientation, boolean reverseLayout) {
super(view.getContext(), orientation, reverseLayout);
this.view = view;
this.overScrollMode = ViewCompat.getOverScrollMode(view);
}
public void setOverScrollMode(int overScrollMode) {
if (overScrollMode < ViewCompat.OVER_SCROLL_ALWAYS || overScrollMode > ViewCompat.OVER_SCROLL_NEVER)
throw new IllegalArgumentException("Unknown overscroll mode: " + overScrollMode);
if (this.view == null) throw new IllegalStateException("view == null");
this.overScrollMode = overScrollMode;
ViewCompat.setOverScrollMode(view, overScrollMode);
}
public static int makeUnspecifiedSpec() {
return View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
}
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
final boolean hasWidthSize = widthMode != View.MeasureSpec.UNSPECIFIED;
final boolean hasHeightSize = heightMode != View.MeasureSpec.UNSPECIFIED;
final boolean exactWidth = widthMode == View.MeasureSpec.EXACTLY;
final boolean exactHeight = heightMode == View.MeasureSpec.EXACTLY;
final int unspecified = makeUnspecifiedSpec();
if (exactWidth && exactHeight) {
// in case of exact calculations for both dimensions let's use default "onMeasure" implementation
super.onMeasure(recycler, state, widthSpec, heightSpec);
return;
}
final boolean vertical = getOrientation() == VERTICAL;
initChildDimensions(widthSize, heightSize, vertical);
int width = 0;
int height = 0;
// it's possible to get scrap views in recycler which are bound to old (invalid) adapter entities. This
// happens because their invalidation happens after "onMeasure" method. As a workaround let's clear the
// recycler now (it should not cause any performance issues while scrolling as "onMeasure" is never
// called whiles scrolling)
recycler.clear();
final int stateItemCount = state.getItemCount();
final int adapterItemCount = getItemCount();
// adapter always contains actual data while state might contain old data (f.e. data before the animation is
// done). As we want to measure the view with actual data we must use data from the adapter and not from the
// state
for (int i = 0; i < adapterItemCount; i++) {
if (vertical) {
if (!hasChildSize) {
if (i < stateItemCount) {
// we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
// we will use previously calculated dimensions
measureChild(recycler, i, widthSize, unspecified, childDimensions);
} else {
logMeasureWarning(i);
}
}
height += childDimensions[CHILD_HEIGHT];
if (i == 0) {
width = childDimensions[CHILD_WIDTH];
}
if (hasHeightSize && height >= heightSize) {
break;
}
} else {
if (!hasChildSize) {
if (i < stateItemCount) {
// we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
// we will use previously calculated dimensions
measureChild(recycler, i, unspecified, heightSize, childDimensions);
} else {
logMeasureWarning(i);
}
}
width += childDimensions[CHILD_WIDTH];
if (i == 0) {
height = childDimensions[CHILD_HEIGHT];
}
if (hasWidthSize && width >= widthSize) {
break;
}
}
}
if (exactWidth) {
width = widthSize;
} else {
width += getPaddingLeft() + getPaddingRight();
if (hasWidthSize) {
width = Math.min(width, widthSize);
}
}
if (exactHeight) {
height = heightSize;
} else {
height += getPaddingTop() + getPaddingBottom();
if (hasHeightSize) {
height = Math.min(height, heightSize);
}
}
setMeasuredDimension(width, height);
if (view != null && overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS) {
final boolean fit = (vertical && (!hasHeightSize || height < heightSize))
|| (!vertical && (!hasWidthSize || width < widthSize));
ViewCompat.setOverScrollMode(view, fit ? ViewCompat.OVER_SCROLL_NEVER : ViewCompat.OVER_SCROLL_ALWAYS);
}
}
private void logMeasureWarning(int child) {
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "Can't measure child #" + child + ", previously used dimensions will be reused." +
"To remove this message either use #setChildSize() method or don't run RecyclerView animations");
}
}
private void initChildDimensions(int width, int height, boolean vertical) {
if (childDimensions[CHILD_WIDTH] != 0 || childDimensions[CHILD_HEIGHT] != 0) {
// already initialized, skipping
return;
}
if (vertical) {
childDimensions[CHILD_WIDTH] = width;
childDimensions[CHILD_HEIGHT] = childSize;
} else {
childDimensions[CHILD_WIDTH] = childSize;
childDimensions[CHILD_HEIGHT] = height;
}
}
@Override
public void setOrientation(int orientation) {
// might be called before the constructor of this class is called
//noinspection ConstantConditions
if (childDimensions != null) {
if (getOrientation() != orientation) {
childDimensions[CHILD_WIDTH] = 0;
childDimensions[CHILD_HEIGHT] = 0;
}
}
super.setOrientation(orientation);
}
public void clearChildSize() {
hasChildSize = false;
setChildSize(DEFAULT_CHILD_SIZE);
}
public void setChildSize(int childSize) {
hasChildSize = true;
if (this.childSize != childSize) {
this.childSize = childSize;
requestLayout();
}
}
private void measureChild(RecyclerView.Recycler recycler, int position, int widthSize, int heightSize, int[] dimensions) {
final View child;
try {
child = recycler.getViewForPosition(position);
} catch (IndexOutOfBoundsException e) {
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "LinearLayoutManager doesn't work well with animations. Consider switching them off", e);
}
return;
}
final RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) child.getLayoutParams();
final int hPadding = getPaddingLeft() + getPaddingRight();
final int vPadding = getPaddingTop() + getPaddingBottom();
final int hMargin = p.leftMargin + p.rightMargin;
final int vMargin = p.topMargin + p.bottomMargin;
// we must make insets dirty in order calculateItemDecorationsForChild to work
makeInsetsDirty(p);
// this method should be called before any getXxxDecorationXxx() methods
calculateItemDecorationsForChild(child, tmpRect);
final int hDecoration = getRightDecorationWidth(child) + getLeftDecorationWidth(child);
final int vDecoration = getTopDecorationHeight(child) + getBottomDecorationHeight(child);
final int childWidthSpec = getChildMeasureSpec(widthSize, hPadding + hMargin + hDecoration, p.width, canScrollHorizontally());
final int childHeightSpec = getChildMeasureSpec(heightSize, vPadding + vMargin + vDecoration, p.height, canScrollVertically());
child.measure(childWidthSpec, childHeightSpec);
dimensions[CHILD_WIDTH] = getDecoratedMeasuredWidth(child) + p.leftMargin + p.rightMargin;
dimensions[CHILD_HEIGHT] = getDecoratedMeasuredHeight(child) + p.bottomMargin + p.topMargin;
// as view is recycled let's not keep old measured values
makeInsetsDirty(p);
recycler.recycleView(child);
}
private static void makeInsetsDirty(RecyclerView.LayoutParams p) {
if (!canMakeInsetsDirty) {
return;
}
try {
if (insetsDirtyField == null) {
insetsDirtyField = RecyclerView.LayoutParams.class.getDeclaredField("mInsetsDirty");
insetsDirtyField.setAccessible(true);
}
insetsDirtyField.set(p, true);
} catch (NoSuchFieldException e) {
onMakeInsertDirtyFailed();
} catch (IllegalAccessException e) {
onMakeInsertDirtyFailed();
}
}
private static void onMakeInsertDirtyFailed() {
canMakeInsetsDirty = false;
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "Can't make LayoutParams insets dirty, decorations measurements might be incorrect");
}
}
}
将此 WrapContentLinearLayoutManager 放入您的回收视图
mRecyclerView.setLayoutManager(new WrapContentLinearLayoutManager(activity));
而这在 xml 中（与 parent 中的亲戚）
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:id="@+id/recyclerViewMuseum"
android:scrollbars="vertical"
android:scrollIndicators="none"/>
这应该有效:)
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_marginTop="@dimen/margin_twenty"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginBottom="@dimen/margin_twenty">
</android.support.v7.widget.RecyclerView>
我使用的是 RecyclerView，其中包含带有 TextView 和 ImageView 的 CardView（每张卡片代表一个城市）。我还在每张卡片上都有一个 onClickListener，它会引导我进入城市中的博物馆列表。 （RecyclerView 由 ArrayList 填充）。 列表是由同一个垂直滚动的Cardview组成的RecyclerView
当一个城市只有一个博物馆时，如何在屏幕中央显示唯一的CardView？
这是activity xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.bebbo203.mymuseum.MuseumActivity">
<android.support.v7.widget.RecyclerView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/recyclerViewMuseum"
android:scrollbars="vertical"
android:scrollIndicators="none"
android:gravity="center_horizontal"
/>
</RelativeLayout>
这是 RecyclerView xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:baselineAligned="false"
xmlns:card_view="http://schemas.android.com/apk/res-auto">
<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="150dp"
android:id="@+id/cardView"
card_view:cardCornerRadius="2dp"
card_view:cardUseCompatPadding="true"
android:gravity="center_horizontal"
android:animateLayoutChanges="true"
>
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:layout_width="match_parent"
android:layout_height="150dp"
android:id="@+id/imageViewList"
android:layout_gravity="center_horizontal|top"
android:adjustViewBounds="true"
android:scaleType="centerCrop"/>
<TextView
android:id="@+id/textViewList"
android:layout_width="match_parent"
android:layout_height="150dp"
android:textSize="40sp"
android:textIsSelectable="false"
android:textAlignment="center"
android:gravity="fill"
android:textStyle="bold"
android:layout_weight="1"
android:layout_gravity="center_horizontal|top"/>
</FrameLayout>
</android.support.v7.widget.CardView>
</RelativeLayout>`
感谢您的帮助。
这就是 MainActivity。城市列表。这里一切都很好。
当我点击只有一个博物馆的 Parigi 时，我想在屏幕中央显示单个卡片视图
（如果可能的话，我想让卡片视图从屏幕中央开始，而不是从顶部开始。就像当我打开 activity 时中央卡片视图始终位于中央一样。例如在中心翻译 NationalGallery 维护其他的顺序)
1.Try 当 recyclerview 有 1 个子视图时设置 LayoutParams CENTER_IN_PARENT
2.Or 使用 FrameLayout 作为 recyclerView 的父级并设置 layout_gravity
3.Or 只需计算 cardview 上方的 space 并将 marginTop 设置为 recyclerView 或将 setTranslationY 设置为 recyclerView
4.Or 在 Recylerview.
itemDecaration，高度为 space'
RelativeLayout.LayoutParams rLp = (RelativeLayout.LayoutParams) recyclerView.getLayoutParams();
if(data != null || data.size()>1){
rLp.removeRule(RelativeLayout.CENTER_IN_PARENT);
}else{
rLp.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);
}
recyclerView.setLayoutParams(rLp);
当recyclerView只有一个child时使用这个LayoutManager:
import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
public class FullyLinearLayoutManager extends LinearLayoutManager {
private static final String TAG = FullyLinearLayoutManager.class.getSimpleName();
private MeasureEndListener mMeasureEndListener;
public FullyLinearLayoutManager(Context context) {
super(context);
}
private float divHeight =0;
public FullyLinearLayoutManager(Context context,float height) {
super(context);
divHeight = height;
}
public FullyLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
private int[] mMeasuredDimension = new int[2];
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
Log.i(TAG, "onMeasure called. \nwidthMode " + widthMode
+ " \nheightMode " + heightSpec
+ " \nwidthSize " + widthSize
+ " \nheightSize " + heightSize
+ " \ngetItemCount() " + getItemCount());
int width = 0;
int height = 0;
for (int i = 0; i < getItemCount(); i++) {
measureScrapChild(recycler, i,
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
mMeasuredDimension);
if (getOrientation() == HORIZONTAL) {
width = width + mMeasuredDimension[0];
if (i == 0) {
height = mMeasuredDimension[1];
}
} else {
// LogUtils.e(mMeasuredDimension[1]);
height = height + mMeasuredDimension[1];
if(i!= getItemCount()-1){
height += divHeight;
// LogUtils.e(divHeight + "xxx add"+DensityUtils.dp2px(divHeight));
}else{
height += 2*divHeight;
// LogUtils.e(divHeight+ "xxx no add"+ DensityUtils.dp2px(divHeight));
}
if (i == 0) {
width = mMeasuredDimension[0];
}
}
}
switch (widthMode) {
case View.MeasureSpec.EXACTLY:
width = widthSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
switch (heightMode) {
case View.MeasureSpec.EXACTLY:
height = heightSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
if(mMeasureEndListener!=null){
mMeasureEndListener.onMeasureEnd(width,height);
// new Thread().interrupt();
}
setMeasuredDimension(width, height);
}
private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
int heightSpec, int[] measuredDimension) {
try {
View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException
if (view != null) {
RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
getPaddingLeft() + getPaddingRight(), p.width);
int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
getPaddingTop() + getPaddingBottom(), p.height);
view.measure(childWidthSpec, childHeightSpec);
measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
recycler.recycleView(view);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
}
}
public interface MeasureEndListener{
void onMeasureEnd(int width,int height);
}
public void setMeasureEndListener(MeasureEndListener mMeasureEndListener){
this.mMeasureEndListener = mMeasureEndListener;
}
}
当只有一项或多项时，尝试将高度设置为 RecyclerView。
请参阅 this topic 以执行此操作。当只有一项时，将 RecyclerView 设置为 WRAP_CONTENT。当有更多一项时，将 RecyclerView 设置为 MATCH_CONTENT。祝你好运！
我已经实现了简单的 HelloWorld 应用程序，它显示了城市列表并根据它拥有的博物馆数量显示了全尺寸城市名片或它的居中包装版本。
（是的，我不太擅长艺术:-)）
这是我的做法。
长话短说：
关键是ItemDecoration：设置合适的项目偏移量，你会得到你需要的;这是我的做法：
RecyclerView recyclerViewMuseum = (RecyclerView)findViewById(R.id.recyclerViewMuseum);
recyclerViewMuseum.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
recyclerViewMuseum.setAdapter(adapter);
recyclerViewMuseum.addItemDecoration(new RecyclerView.ItemDecoration() {
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
if (view instanceof CityWithOneMuseumCardView) {
int totalWidth = parent.getWidth();
int cardWidth = getResources().getDimensionPixelOffset(R.dimen.small_card_width);
int sidePadding = (totalWidth - cardWidth) / 2;
sidePadding = Math.max(0, sidePadding);
outRect.set(sidePadding, 0, sidePadding, 0);
}
}
});
这是我的模型 - City 和 Museum 类:
public class Museum {
public String title;
public Museum(String title) {
this.title = title;
}
}
public class City {
public String title;
public int imageRes;
public List<Museum> museums = new ArrayList<>();
public City(String title, int imageRes) {
this.title = title;
this.imageRes = imageRes;
}
}
然后是浏览量：CityWithManyMuseumsCardView 和 CityWithOneMuseumCardView。他们都在使用辅助接口 IItemDisplayer.
public class CityWithOneMuseumCardView extends CardView implements IItemDisplayer<City> {
public CityWithOneMuseumCardView(Context context) {
super(context);
LayoutInflater.from(context).inflate(R.layout.one_museum_layout, this);
}
@Override
public void displayItem(City city) {
TextView cityTitleTextView = (TextView)findViewById(R.id.cityTitleTextView);
cityTitleTextView.setText(city.title);
}
}
public class CityWithManyMuseumsCardView extends CardView implements IItemDisplayer<City> {
public CityWithManyMuseumsCardView(Context context) {
super(context);
LayoutInflater.from(context).inflate(R.layout.many_museums_layout, this);
}
@Override
public void displayItem(City city) {
ImageView cityBackgroundImageView = (ImageView)findViewById(R.id.cityBackgroundImageView);
cityBackgroundImageView.setImageResource(city.imageRes);
TextView cityTitleTextView = (TextView)findViewById(R.id.cityTitleTextView);
cityTitleTextView.setText(city.title);
TextView cityNumberOrMuseumsTextView = (TextView)findViewById(R.id.cityNumberOrMuseumsTextView);
cityNumberOrMuseumsTextView.setText(String.valueOf(city.museums.size()));
}
}
public interface IItemDisplayer<TItem> {
public void displayItem(TItem item);
}
以及他们的布局：
<!-- One Museum card -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:background="#BB2050AB"
android:layout_width="@dimen/small_card_width"
android:layout_height="200dp">
<TextView
android:background="#AA000000"
android:textColor="#FFFFFF"
android:text="Only one museum available"
android:textSize="16sp"
android:padding="4dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/cityTitleTextView"
android:layout_gravity="bottom"
android:background="#AAFFFFFF"
android:textColor="#000000"
android:textSize="24sp"
android:paddingStart="16dp"
android:paddingEnd="16dp"
android:gravity="center"
android:layout_width="match_parent"
android:layout_height="48dp" />
</FrameLayout>
<!-- Many museums card -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="240dp">
<ImageView
android:id="@+id/cityBackgroundImageView"
android:scaleType="fitXY"
android:layout_width="500dp"
android:layout_height="match_parent" />
<TextView
android:id="@+id/cityNumberOrMuseumsTextView"
android:layout_gravity="top|end"
android:background="#AA000000"
android:textColor="#FFFFFF"
android:textSize="16sp"
android:padding="4dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/cityTitleTextView"
android:layout_gravity="bottom"
android:background="#AA000000"
android:textColor="#FFFFFF"
android:textSize="24sp"
android:paddingStart="16dp"
android:paddingEnd="16dp"
android:gravity="center_vertical"
android:layout_width="match_parent"
android:layout_height="48dp" />
</FrameLayout>
然后我们需要为我们的 RecyclerView 创建一个适配器
CityAdapter.java
public class CityAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
final static int ITEM_TYPE_MANY_MUSEUMS = 0;
final static int ITEM_TYPE_ONE_MUSEUM = 1;
private List<City> items;
public CityAdapter(List<City> items) {
this.items = items;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
switch (viewType) {
case ITEM_TYPE_MANY_MUSEUMS:
return new ViewHolder(new CityWithManyMuseumsCardView(viewGroup.getContext()));
case ITEM_TYPE_ONE_MUSEUM:
return new ViewHolder(new CityWithOneMuseumCardView(viewGroup.getContext()));
default:
throw new IllegalArgumentException(String.format("Unexpected viewType: %d", viewType));
}
}
@Override
public int getItemViewType(int position) {
if (items == null || items.size() < position) {
throw new IllegalArgumentException("Wrong position!");
}
if (items.get(position).museums.size() > 1) {
return ITEM_TYPE_MANY_MUSEUMS;
} else if (items.get(position).museums.size() == 1){
return ITEM_TYPE_ONE_MUSEUM;
}
throw new IllegalArgumentException("Wrong number of museums!");
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
((IItemDisplayer<City>) holder.itemView).displayItem(items.get(position));
}
@Override
public int getItemCount() {
return items.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
public ViewHolder(View itemView) {
super(itemView);
}
}
}
我已将此项目上传到我的保管箱 - 欢迎 check it out！希望对你有帮助。
你能试试这个吗:
import android.content.Context;
import android.graphics.Rect;
import android.support.v4.view.ViewCompat;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import java.lang.reflect.Field;
/**
* {@link android.support.v7.widget.LinearLayoutManager} which wraps its content. Note that this class will always
* wrap the content regardless of {@link android.support.v7.widget.RecyclerView} layout parameters.
* <p/>
* Now it's impossible to run add/remove animations with child views which have arbitrary dimensions (height for
* VERTICAL orientation and width for HORIZONTAL). However if child views have fixed dimensions
* {@link #setChildSize(int)} method might be used to let the layout manager know how big they are going to be.
* If animations are not used at all then a normal measuring procedure will run and child views will be measured during
* the measure pass.
*/
public class WrapContentLinearLayoutManager extends android.support.v7.widget.LinearLayoutManager {
private static boolean canMakeInsetsDirty = true;
private static Field insetsDirtyField = null;
private static final int CHILD_WIDTH = 0;
private static final int CHILD_HEIGHT = 1;
private static final int DEFAULT_CHILD_SIZE = 100;
private final int[] childDimensions = new int[2];
private final RecyclerView view;
private int childSize = DEFAULT_CHILD_SIZE;
private boolean hasChildSize;
private int overScrollMode = ViewCompat.OVER_SCROLL_ALWAYS;
private final Rect tmpRect = new Rect();
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(Context context) {
super(context);
this.view = null;
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
this.view = null;
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(RecyclerView view) {
super(view.getContext());
this.view = view;
this.overScrollMode = ViewCompat.getOverScrollMode(view);
}
@SuppressWarnings("UnusedDeclaration")
public WrapContentLinearLayoutManager(RecyclerView view, int orientation, boolean reverseLayout) {
super(view.getContext(), orientation, reverseLayout);
this.view = view;
this.overScrollMode = ViewCompat.getOverScrollMode(view);
}
public void setOverScrollMode(int overScrollMode) {
if (overScrollMode < ViewCompat.OVER_SCROLL_ALWAYS || overScrollMode > ViewCompat.OVER_SCROLL_NEVER)
throw new IllegalArgumentException("Unknown overscroll mode: " + overScrollMode);
if (this.view == null) throw new IllegalStateException("view == null");
this.overScrollMode = overScrollMode;
ViewCompat.setOverScrollMode(view, overScrollMode);
}
public static int makeUnspecifiedSpec() {
return View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
}
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
final boolean hasWidthSize = widthMode != View.MeasureSpec.UNSPECIFIED;
final boolean hasHeightSize = heightMode != View.MeasureSpec.UNSPECIFIED;
final boolean exactWidth = widthMode == View.MeasureSpec.EXACTLY;
final boolean exactHeight = heightMode == View.MeasureSpec.EXACTLY;
final int unspecified = makeUnspecifiedSpec();
if (exactWidth && exactHeight) {
// in case of exact calculations for both dimensions let's use default "onMeasure" implementation
super.onMeasure(recycler, state, widthSpec, heightSpec);
return;
}
final boolean vertical = getOrientation() == VERTICAL;
initChildDimensions(widthSize, heightSize, vertical);
int width = 0;
int height = 0;
// it's possible to get scrap views in recycler which are bound to old (invalid) adapter entities. This
// happens because their invalidation happens after "onMeasure" method. As a workaround let's clear the
// recycler now (it should not cause any performance issues while scrolling as "onMeasure" is never
// called whiles scrolling)
recycler.clear();
final int stateItemCount = state.getItemCount();
final int adapterItemCount = getItemCount();
// adapter always contains actual data while state might contain old data (f.e. data before the animation is
// done). As we want to measure the view with actual data we must use data from the adapter and not from the
// state
for (int i = 0; i < adapterItemCount; i++) {
if (vertical) {
if (!hasChildSize) {
if (i < stateItemCount) {
// we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
// we will use previously calculated dimensions
measureChild(recycler, i, widthSize, unspecified, childDimensions);
} else {
logMeasureWarning(i);
}
}
height += childDimensions[CHILD_HEIGHT];
if (i == 0) {
width = childDimensions[CHILD_WIDTH];
}
if (hasHeightSize && height >= heightSize) {
break;
}
} else {
if (!hasChildSize) {
if (i < stateItemCount) {
// we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
// we will use previously calculated dimensions
measureChild(recycler, i, unspecified, heightSize, childDimensions);
} else {
logMeasureWarning(i);
}
}
width += childDimensions[CHILD_WIDTH];
if (i == 0) {
height = childDimensions[CHILD_HEIGHT];
}
if (hasWidthSize && width >= widthSize) {
break;
}
}
}
if (exactWidth) {
width = widthSize;
} else {
width += getPaddingLeft() + getPaddingRight();
if (hasWidthSize) {
width = Math.min(width, widthSize);
}
}
if (exactHeight) {
height = heightSize;
} else {
height += getPaddingTop() + getPaddingBottom();
if (hasHeightSize) {
height = Math.min(height, heightSize);
}
}
setMeasuredDimension(width, height);
if (view != null && overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS) {
final boolean fit = (vertical && (!hasHeightSize || height < heightSize))
|| (!vertical && (!hasWidthSize || width < widthSize));
ViewCompat.setOverScrollMode(view, fit ? ViewCompat.OVER_SCROLL_NEVER : ViewCompat.OVER_SCROLL_ALWAYS);
}
}
private void logMeasureWarning(int child) {
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "Can't measure child #" + child + ", previously used dimensions will be reused." +
"To remove this message either use #setChildSize() method or don't run RecyclerView animations");
}
}
private void initChildDimensions(int width, int height, boolean vertical) {
if (childDimensions[CHILD_WIDTH] != 0 || childDimensions[CHILD_HEIGHT] != 0) {
// already initialized, skipping
return;
}
if (vertical) {
childDimensions[CHILD_WIDTH] = width;
childDimensions[CHILD_HEIGHT] = childSize;
} else {
childDimensions[CHILD_WIDTH] = childSize;
childDimensions[CHILD_HEIGHT] = height;
}
}
@Override
public void setOrientation(int orientation) {
// might be called before the constructor of this class is called
//noinspection ConstantConditions
if (childDimensions != null) {
if (getOrientation() != orientation) {
childDimensions[CHILD_WIDTH] = 0;
childDimensions[CHILD_HEIGHT] = 0;
}
}
super.setOrientation(orientation);
}
public void clearChildSize() {
hasChildSize = false;
setChildSize(DEFAULT_CHILD_SIZE);
}
public void setChildSize(int childSize) {
hasChildSize = true;
if (this.childSize != childSize) {
this.childSize = childSize;
requestLayout();
}
}
private void measureChild(RecyclerView.Recycler recycler, int position, int widthSize, int heightSize, int[] dimensions) {
final View child;
try {
child = recycler.getViewForPosition(position);
} catch (IndexOutOfBoundsException e) {
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "LinearLayoutManager doesn't work well with animations. Consider switching them off", e);
}
return;
}
final RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) child.getLayoutParams();
final int hPadding = getPaddingLeft() + getPaddingRight();
final int vPadding = getPaddingTop() + getPaddingBottom();
final int hMargin = p.leftMargin + p.rightMargin;
final int vMargin = p.topMargin + p.bottomMargin;
// we must make insets dirty in order calculateItemDecorationsForChild to work
makeInsetsDirty(p);
// this method should be called before any getXxxDecorationXxx() methods
calculateItemDecorationsForChild(child, tmpRect);
final int hDecoration = getRightDecorationWidth(child) + getLeftDecorationWidth(child);
final int vDecoration = getTopDecorationHeight(child) + getBottomDecorationHeight(child);
final int childWidthSpec = getChildMeasureSpec(widthSize, hPadding + hMargin + hDecoration, p.width, canScrollHorizontally());
final int childHeightSpec = getChildMeasureSpec(heightSize, vPadding + vMargin + vDecoration, p.height, canScrollVertically());
child.measure(childWidthSpec, childHeightSpec);
dimensions[CHILD_WIDTH] = getDecoratedMeasuredWidth(child) + p.leftMargin + p.rightMargin;
dimensions[CHILD_HEIGHT] = getDecoratedMeasuredHeight(child) + p.bottomMargin + p.topMargin;
// as view is recycled let's not keep old measured values
makeInsetsDirty(p);
recycler.recycleView(child);
}
private static void makeInsetsDirty(RecyclerView.LayoutParams p) {
if (!canMakeInsetsDirty) {
return;
}
try {
if (insetsDirtyField == null) {
insetsDirtyField = RecyclerView.LayoutParams.class.getDeclaredField("mInsetsDirty");
insetsDirtyField.setAccessible(true);
}
insetsDirtyField.set(p, true);
} catch (NoSuchFieldException e) {
onMakeInsertDirtyFailed();
} catch (IllegalAccessException e) {
onMakeInsertDirtyFailed();
}
}
private static void onMakeInsertDirtyFailed() {
canMakeInsetsDirty = false;
if (BuildConfig.DEBUG) {
Log.w("LinearLayoutManager", "Can't make LayoutParams insets dirty, decorations measurements might be incorrect");
}
}
}
将此 WrapContentLinearLayoutManager 放入您的回收视图
mRecyclerView.setLayoutManager(new WrapContentLinearLayoutManager(activity));
而这在 xml 中（与 parent 中的亲戚）
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:id="@+id/recyclerViewMuseum"
android:scrollbars="vertical"
android:scrollIndicators="none"/>
这应该有效:)
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_marginTop="@dimen/margin_twenty"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginBottom="@dimen/margin_twenty">
</android.support.v7.widget.RecyclerView>