CollapsingToolbarLayout 无法识别滚动条
CollapsingToolbarLayout doesn't recognize scroll fling
我创建了一个简单的 CollapsingToolbarLayout，它非常有用。我的问题是，如果我尝试在 nestedscrollview 上使用快速滚动，它会在我松开手指时停止。正常滚动工作正常。
我的活动代码是未更改=>自动生成空activity。 （我刚刚在 android studio 中点击了 create new empty activity 并编辑了 XML）。
我在这里读到，图像视图上的滚动手势本身有问题，但滚动本身没有问题：see here。
我尝试通过 java 代码激活 "smooth scrolling"。似乎如果我滚动得足够远以至于图像视图不再可见，那么就会识别出快速手势。
TLDR:为什么只要 imageview 可见，fling 手势就不起作用？
我的 XML 代码如下所示：
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<android.support.design.widget.AppBarLayout
android:id="@+id/profile_app_bar_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:fitsSystemWindows="true">
<android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/profile_collapsing_toolbar_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginStart="48dp"
app:expandedTitleMarginEnd="64dp"
android:fitsSystemWindows="true">
<ImageView
android:id="@+id/image"
android:layout_width="match_parent"
android:layout_height="420dp"
android:scaleType="centerCrop"
android:fitsSystemWindows="true"
android:src="@drawable/headerbg"
android:maxHeight="192dp"
app:layout_collapseMode="parallax"/>
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
app:layout_collapseMode="pin" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
app:layout_anchor="@id/profile_app_bar_layout"
app:layout_anchorGravity="bottom|right|end"
android:layout_height="@dimen/fab_size_normal"
android:layout_width="@dimen/fab_size_normal"
app:elevation="2dp"
app:pressedTranslationZ="12dp"
android:layout_marginRight="8dp"
android:layout_marginEnd="8dp"/>
<android.support.v4.widget.NestedScrollView
android:id="@+id/profile_content_scroll"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:layout_gravity="fill_vertical"
android:minHeight="192dp"
android:overScrollMode="ifContentScrolls"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/LoremIpsum"/>
</RelativeLayout>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
帮我解决了这个问题。像这样创建自定义 AppBarLayout.Behavior：
public final class FlingBehavior extends AppBarLayout.Behavior {
private static final int TOP_CHILD_FLING_THRESHOLD = 3;
private boolean isPositive;
public FlingBehavior() {
}
public FlingBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
if (velocityY > 0 && !isPositive || velocityY < 0 && isPositive) {
velocityY = velocityY * -1;
}
if (target instanceof RecyclerView && velocityY < 0) {
final RecyclerView recyclerView = (RecyclerView) target;
final View firstChild = recyclerView.getChildAt(0);
final int childAdapterPosition = recyclerView.getChildAdapterPosition(firstChild);
consumed = childAdapterPosition > TOP_CHILD_FLING_THRESHOLD;
}
return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
isPositive = dy > 0;
}
}
并将其添加到 AppBarLayout 中，如下所示：
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
...
app:layout_behavior="com.example.test.FlingBehavior">
我知道这个问题是一年多前提出的，但这个问题似乎在 Support/Design 库中仍未得到解决。您可以 star this 发布，使其在优先级队列中更靠前。
也就是说，我为此尝试了大多数已发布的解决方案，包括 patrick-iv 的解决方案，但没有成功。如果在 onPreNestedScroll() 中检测到一组特定条件，我能够开始工作的唯一方法是模仿并以编程方式调用它。在调试的几个小时内，我注意到 onNestedFling() 从未在向上（向下滚动）滑动时被调用，并且似乎被过早地消耗掉了。我不能 100% 肯定地说这适用于 100% 的实现，但它对我的使用来说已经足够好了，所以我最终接受了这个，尽管它很老套而且绝对不是我想做的。
public class NestedScrollViewBehavior extends AppBarLayout.Behavior {
// Lower value means fling action is more easily triggered
static final int MIN_DY_DELTA = 4;
// Lower values mean less velocity, higher means higher velocity
static final int FLING_FACTOR = 20;
int mTotalDy;
int mPreviousDy;
WeakReference<AppBarLayout> mPreScrollChildRef;
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
// Reset the total fling delta distance if the user starts scrolling back up
if(dy < 0) {
mTotalDy = 0;
}
// Only track move distance if the movement is positive (since the bug is only present
// in upward flings), equal to the consumed value and the move distance is greater
// than the minimum difference value
if(dy > 0 && consumed[1] == dy && MIN_DY_DELTA < Math.abs(mPreviousDy - dy)) {
mPreScrollChildRef = new WeakReference<>(child);
mTotalDy += dy * FLING_FACTOR;
}
mPreviousDy = dy;
}
@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,
View directTargetChild, View target, int nestedScrollAxes) {
// Stop any previous fling animations that may be running
onNestedFling(parent, child, target, 0, 0, false);
return super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes);
}
@Override
public void onStopNestedScroll(CoordinatorLayout parent, AppBarLayout abl, View target) {
if(mTotalDy > 0 && mPreScrollChildRef != null && mPreScrollChildRef.get() != null) {
// Programmatically trigger fling if all conditions are met
onNestedFling(parent, mPreScrollChildRef.get(), target, 0, mTotalDy, false);
mTotalDy = 0;
mPreviousDy = 0;
mPreScrollChildRef = null;
}
super.onStopNestedScroll(parent, abl, target);
}
}
并将其应用到 AppBar
AppBarLayout scrollView = (AppBarLayout)findViewById(R.id.appbar);
CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams)scrollView.getLayoutParams();
params.setBehavior(new NestedScrollViewBehavior());
我尝试了 Floofer 的解决方案，但它对我来说仍然不够好。所以我想出了一个更好的他的行为版本。 AppBarLayout 现在可以在滑动时平滑地展开和折叠。
注意： 我使用反射来解决这个问题，因此它可能无法完美地与不同于 25.0.0 的 Android 设计库版本一起工作.
public class SmoothScrollBehavior extends AppBarLayout.Behavior {
private static final String TAG = "SmoothScrollBehavior";
//The higher this value is, the faster the user must scroll for the AppBarLayout to collapse by itself
private static final int SCROLL_SENSIBILITY = 5;
//The real fling velocity calculation seems complex, in this case it is simplified with a multiplier
private static final int FLING_VELOCITY_MULTIPLIER = 60;
private boolean alreadyFlung = false;
private boolean request = false;
private boolean expand = false;
private int velocity = 0;
private int nestedScrollViewId;
public SmoothScrollBehavior(int nestedScrollViewId) {
this.nestedScrollViewId = nestedScrollViewId;
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
if(Math.abs(dy) >= SCROLL_SENSIBILITY) {
request = true;
expand = dy < 0;
velocity = dy * FLING_VELOCITY_MULTIPLIER;
} else {
request = false;
}
}
@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,
View directTargetChild, View target, int nestedScrollAxes) {
request = false;
return super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes);
}
@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout appBarLayout, View target) {
if(request) {
NestedScrollView nestedScrollView = (NestedScrollView) coordinatorLayout.findViewById(nestedScrollViewId);
if (expand) {
//No need to force expand if it is already ready expanding
if (nestedScrollView.getScrollY() > 0) {
int finalY = getPredictedScrollY(nestedScrollView);
if (finalY <= 0) {
//since onNestedFling does not work to expand the AppBarLayout, we need to manually expand it
expandAppBarLayoutWithVelocity(coordinatorLayout, appBarLayout, velocity);
}
}
} else {
//onNestedFling will collapse the AppBarLayout with an animation time relative to the velocity
onNestedFling(coordinatorLayout, appBarLayout, target, 0, velocity, true);
if(!alreadyFlung) {
//TODO wait for AppBarLayout to be collapsed before scrolling for even smoother visual
nestedScrollView.fling(velocity);
}
}
}
alreadyFlung = false;
super.onStopNestedScroll(coordinatorLayout, appBarLayout, target);
}
private int getPredictedScrollY(NestedScrollView nestedScrollView) {
int finalY = 0;
try {
//With reflection, we can get the ScrollerCompat from the NestedScrollView to predict where the scroll will end
Field scrollerField = nestedScrollView.getClass().getDeclaredField("mScroller");
scrollerField.setAccessible(true);
Object object = scrollerField.get(nestedScrollView);
ScrollerCompat scrollerCompat = (ScrollerCompat) object;
finalY = scrollerCompat.getFinalY();
} catch (Exception e ) {
e.printStackTrace();
//If the reflection fails, it will return 0, which means the scroll has reached top
Log.e(TAG, "Failed to get mScroller field from NestedScrollView through reflection. Will assume that the scroll reached the top.");
}
return finalY;
}
private void expandAppBarLayoutWithVelocity(CoordinatorLayout coordinatorLayout, AppBarLayout appBarLayout, float velocity) {
try {
//With reflection, we can call the private method of Behavior that expands the AppBarLayout with specified velocity
Method animateOffsetTo = getClass().getSuperclass().getDeclaredMethod("animateOffsetTo", CoordinatorLayout.class, AppBarLayout.class, int.class, float.class);
animateOffsetTo.setAccessible(true);
animateOffsetTo.invoke(this, coordinatorLayout, appBarLayout, 0, velocity);
} catch (Exception e) {
e.printStackTrace();
//If the reflection fails, we fall back to the public method setExpanded that expands the AppBarLayout with a fixed velocity
Log.e(TAG, "Failed to get animateOffsetTo method from AppBarLayout.Behavior through reflection. Falling back to setExpanded.");
appBarLayout.setExpanded(true, true);
}
}
@Override
public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY) {
alreadyFlung = true;
return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
}
}
要使用它，请为您的 AppBarLayout 设置一个新的行为。
AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.app_bar);
CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) appBarLayout.getLayoutParams();
params.setBehavior(new SmoothScrollBehavior(R.id.nested_scroll_view));
我对 CollapsingToolbarLayout 和 ImageView 以及 NestedScrollView 有完全相同的问题。手指松开时滚动停止。
但是，我注意到了一些奇怪的事情。如果您开始用手指从带有 OnClickListener 的视图（例如 Button）滚动，快速滚动效果很好。
因此我用一个奇怪的解决方案修复了它。在 NestedScrollView 的直接子级上设置 OnClickListener（什么也不做）。然后完美运行！
<android.support.v4.widget.NestedScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<LinearLayout
android:id="@+id/content_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<!-- Page Content -->
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
给直接子（LinearLayout）一个id并在Activity
中设置OnClickListener
ViewGroup mContentContainer = (ViewGroup) findViewById(R.id.content_container);
mContentContainer.setOnClickListener(this);
@Override
public void onClick(View view) {
int viewId = view.getId();
}
备注：
使用支持设计库 25.0.1 测试
CollapsingToolbarLayout with scrollFlags="scroll|enterAlwaysCollapsed"
case MotionEvent.ACTION_UP:
if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(velocityTracker,
mActivePointerId);
if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
flingWithNestedDispatch(-initialVelocity);
} else if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0,
getScrollRange())) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
mActivePointerId = INVALID_POINTER;
endDrag();
break;
当我有时在 NestedScrollView 上使用滑动滚动时 "mIsBeingDragged = false"，所以 NestedScrollView 不发送滑动事件。
当我删除 if (mIsBeingDragged) 语句时。
case MotionEvent.ACTION_UP:
//if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(velocityTracker,
mActivePointerId);
if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
flingWithNestedDispatch(-initialVelocity);
} else if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0,
getScrollRange())) {
ViewCompat.postInvalidateOnAnimation(this);
}
//}
mActivePointerId = INVALID_POINTER;
endDrag();
break;
不会有问题。但不知道会引起什么严重的问题
我只是把它贴在这里，以免其他人在评论中错过它。 works beautifully, but kudos to 的回答指出了一个更简单的方法。与其以编程方式在 Child of the NestedScrollView 上实现 OnClick 方法，更好的方法是在 xml 中为 child.
设置 clickable=true
（使用与 相同的示例）
<android.support.v4.widget.NestedScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<LinearLayout
android:id="@+id/content_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:clickable="true" > <!-- new -->
<!-- Page Content -->
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
我创建了一个简单的 CollapsingToolbarLayout，它非常有用。我的问题是，如果我尝试在 nestedscrollview 上使用快速滚动，它会在我松开手指时停止。正常滚动工作正常。
我的活动代码是未更改=>自动生成空activity。 （我刚刚在 android studio 中点击了 create new empty activity 并编辑了 XML）。
我在这里读到，图像视图上的滚动手势本身有问题，但滚动本身没有问题：see here。
我尝试通过 java 代码激活 "smooth scrolling"。似乎如果我滚动得足够远以至于图像视图不再可见，那么就会识别出快速手势。
TLDR:为什么只要 imageview 可见，fling 手势就不起作用？ 我的 XML 代码如下所示：
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<android.support.design.widget.AppBarLayout
android:id="@+id/profile_app_bar_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:fitsSystemWindows="true">
<android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/profile_collapsing_toolbar_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
app:contentScrim="?attr/colorPrimary"
app:expandedTitleMarginStart="48dp"
app:expandedTitleMarginEnd="64dp"
android:fitsSystemWindows="true">
<ImageView
android:id="@+id/image"
android:layout_width="match_parent"
android:layout_height="420dp"
android:scaleType="centerCrop"
android:fitsSystemWindows="true"
android:src="@drawable/headerbg"
android:maxHeight="192dp"
app:layout_collapseMode="parallax"/>
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
app:layout_collapseMode="pin" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
app:layout_anchor="@id/profile_app_bar_layout"
app:layout_anchorGravity="bottom|right|end"
android:layout_height="@dimen/fab_size_normal"
android:layout_width="@dimen/fab_size_normal"
app:elevation="2dp"
app:pressedTranslationZ="12dp"
android:layout_marginRight="8dp"
android:layout_marginEnd="8dp"/>
<android.support.v4.widget.NestedScrollView
android:id="@+id/profile_content_scroll"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:layout_gravity="fill_vertical"
android:minHeight="192dp"
android:overScrollMode="ifContentScrolls"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/LoremIpsum"/>
</RelativeLayout>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
AppBarLayout.Behavior：
public final class FlingBehavior extends AppBarLayout.Behavior {
private static final int TOP_CHILD_FLING_THRESHOLD = 3;
private boolean isPositive;
public FlingBehavior() {
}
public FlingBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
if (velocityY > 0 && !isPositive || velocityY < 0 && isPositive) {
velocityY = velocityY * -1;
}
if (target instanceof RecyclerView && velocityY < 0) {
final RecyclerView recyclerView = (RecyclerView) target;
final View firstChild = recyclerView.getChildAt(0);
final int childAdapterPosition = recyclerView.getChildAdapterPosition(firstChild);
consumed = childAdapterPosition > TOP_CHILD_FLING_THRESHOLD;
}
return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
isPositive = dy > 0;
}
}
并将其添加到 AppBarLayout 中，如下所示：
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
...
app:layout_behavior="com.example.test.FlingBehavior">
我知道这个问题是一年多前提出的，但这个问题似乎在 Support/Design 库中仍未得到解决。您可以 star this 发布，使其在优先级队列中更靠前。
也就是说，我为此尝试了大多数已发布的解决方案，包括 patrick-iv 的解决方案，但没有成功。如果在 onPreNestedScroll() 中检测到一组特定条件，我能够开始工作的唯一方法是模仿并以编程方式调用它。在调试的几个小时内，我注意到 onNestedFling() 从未在向上（向下滚动）滑动时被调用，并且似乎被过早地消耗掉了。我不能 100% 肯定地说这适用于 100% 的实现，但它对我的使用来说已经足够好了，所以我最终接受了这个，尽管它很老套而且绝对不是我想做的。
public class NestedScrollViewBehavior extends AppBarLayout.Behavior {
// Lower value means fling action is more easily triggered
static final int MIN_DY_DELTA = 4;
// Lower values mean less velocity, higher means higher velocity
static final int FLING_FACTOR = 20;
int mTotalDy;
int mPreviousDy;
WeakReference<AppBarLayout> mPreScrollChildRef;
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
// Reset the total fling delta distance if the user starts scrolling back up
if(dy < 0) {
mTotalDy = 0;
}
// Only track move distance if the movement is positive (since the bug is only present
// in upward flings), equal to the consumed value and the move distance is greater
// than the minimum difference value
if(dy > 0 && consumed[1] == dy && MIN_DY_DELTA < Math.abs(mPreviousDy - dy)) {
mPreScrollChildRef = new WeakReference<>(child);
mTotalDy += dy * FLING_FACTOR;
}
mPreviousDy = dy;
}
@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,
View directTargetChild, View target, int nestedScrollAxes) {
// Stop any previous fling animations that may be running
onNestedFling(parent, child, target, 0, 0, false);
return super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes);
}
@Override
public void onStopNestedScroll(CoordinatorLayout parent, AppBarLayout abl, View target) {
if(mTotalDy > 0 && mPreScrollChildRef != null && mPreScrollChildRef.get() != null) {
// Programmatically trigger fling if all conditions are met
onNestedFling(parent, mPreScrollChildRef.get(), target, 0, mTotalDy, false);
mTotalDy = 0;
mPreviousDy = 0;
mPreScrollChildRef = null;
}
super.onStopNestedScroll(parent, abl, target);
}
}
并将其应用到 AppBar
AppBarLayout scrollView = (AppBarLayout)findViewById(R.id.appbar);
CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams)scrollView.getLayoutParams();
params.setBehavior(new NestedScrollViewBehavior());
我尝试了 Floofer 的解决方案，但它对我来说仍然不够好。所以我想出了一个更好的他的行为版本。 AppBarLayout 现在可以在滑动时平滑地展开和折叠。
注意： 我使用反射来解决这个问题，因此它可能无法完美地与不同于 25.0.0 的 Android 设计库版本一起工作.
public class SmoothScrollBehavior extends AppBarLayout.Behavior {
private static final String TAG = "SmoothScrollBehavior";
//The higher this value is, the faster the user must scroll for the AppBarLayout to collapse by itself
private static final int SCROLL_SENSIBILITY = 5;
//The real fling velocity calculation seems complex, in this case it is simplified with a multiplier
private static final int FLING_VELOCITY_MULTIPLIER = 60;
private boolean alreadyFlung = false;
private boolean request = false;
private boolean expand = false;
private int velocity = 0;
private int nestedScrollViewId;
public SmoothScrollBehavior(int nestedScrollViewId) {
this.nestedScrollViewId = nestedScrollViewId;
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
if(Math.abs(dy) >= SCROLL_SENSIBILITY) {
request = true;
expand = dy < 0;
velocity = dy * FLING_VELOCITY_MULTIPLIER;
} else {
request = false;
}
}
@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,
View directTargetChild, View target, int nestedScrollAxes) {
request = false;
return super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes);
}
@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout appBarLayout, View target) {
if(request) {
NestedScrollView nestedScrollView = (NestedScrollView) coordinatorLayout.findViewById(nestedScrollViewId);
if (expand) {
//No need to force expand if it is already ready expanding
if (nestedScrollView.getScrollY() > 0) {
int finalY = getPredictedScrollY(nestedScrollView);
if (finalY <= 0) {
//since onNestedFling does not work to expand the AppBarLayout, we need to manually expand it
expandAppBarLayoutWithVelocity(coordinatorLayout, appBarLayout, velocity);
}
}
} else {
//onNestedFling will collapse the AppBarLayout with an animation time relative to the velocity
onNestedFling(coordinatorLayout, appBarLayout, target, 0, velocity, true);
if(!alreadyFlung) {
//TODO wait for AppBarLayout to be collapsed before scrolling for even smoother visual
nestedScrollView.fling(velocity);
}
}
}
alreadyFlung = false;
super.onStopNestedScroll(coordinatorLayout, appBarLayout, target);
}
private int getPredictedScrollY(NestedScrollView nestedScrollView) {
int finalY = 0;
try {
//With reflection, we can get the ScrollerCompat from the NestedScrollView to predict where the scroll will end
Field scrollerField = nestedScrollView.getClass().getDeclaredField("mScroller");
scrollerField.setAccessible(true);
Object object = scrollerField.get(nestedScrollView);
ScrollerCompat scrollerCompat = (ScrollerCompat) object;
finalY = scrollerCompat.getFinalY();
} catch (Exception e ) {
e.printStackTrace();
//If the reflection fails, it will return 0, which means the scroll has reached top
Log.e(TAG, "Failed to get mScroller field from NestedScrollView through reflection. Will assume that the scroll reached the top.");
}
return finalY;
}
private void expandAppBarLayoutWithVelocity(CoordinatorLayout coordinatorLayout, AppBarLayout appBarLayout, float velocity) {
try {
//With reflection, we can call the private method of Behavior that expands the AppBarLayout with specified velocity
Method animateOffsetTo = getClass().getSuperclass().getDeclaredMethod("animateOffsetTo", CoordinatorLayout.class, AppBarLayout.class, int.class, float.class);
animateOffsetTo.setAccessible(true);
animateOffsetTo.invoke(this, coordinatorLayout, appBarLayout, 0, velocity);
} catch (Exception e) {
e.printStackTrace();
//If the reflection fails, we fall back to the public method setExpanded that expands the AppBarLayout with a fixed velocity
Log.e(TAG, "Failed to get animateOffsetTo method from AppBarLayout.Behavior through reflection. Falling back to setExpanded.");
appBarLayout.setExpanded(true, true);
}
}
@Override
public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY) {
alreadyFlung = true;
return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
}
}
要使用它，请为您的 AppBarLayout 设置一个新的行为。
AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.app_bar);
CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) appBarLayout.getLayoutParams();
params.setBehavior(new SmoothScrollBehavior(R.id.nested_scroll_view));
我对 CollapsingToolbarLayout 和 ImageView 以及 NestedScrollView 有完全相同的问题。手指松开时滚动停止。
但是，我注意到了一些奇怪的事情。如果您开始用手指从带有 OnClickListener 的视图（例如 Button）滚动，快速滚动效果很好。
因此我用一个奇怪的解决方案修复了它。在 NestedScrollView 的直接子级上设置 OnClickListener（什么也不做）。然后完美运行！
<android.support.v4.widget.NestedScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<LinearLayout
android:id="@+id/content_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<!-- Page Content -->
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
给直接子（LinearLayout）一个id并在Activity
中设置OnClickListenerViewGroup mContentContainer = (ViewGroup) findViewById(R.id.content_container);
mContentContainer.setOnClickListener(this);
@Override
public void onClick(View view) {
int viewId = view.getId();
}
备注：
使用支持设计库 25.0.1 测试
CollapsingToolbarLayout with scrollFlags="scroll|enterAlwaysCollapsed"
case MotionEvent.ACTION_UP:
if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(velocityTracker,
mActivePointerId);
if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
flingWithNestedDispatch(-initialVelocity);
} else if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0,
getScrollRange())) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
mActivePointerId = INVALID_POINTER;
endDrag();
break;
当我有时在 NestedScrollView 上使用滑动滚动时 "mIsBeingDragged = false"，所以 NestedScrollView 不发送滑动事件。
当我删除 if (mIsBeingDragged) 语句时。
case MotionEvent.ACTION_UP:
//if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(velocityTracker,
mActivePointerId);
if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
flingWithNestedDispatch(-initialVelocity);
} else if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0,
getScrollRange())) {
ViewCompat.postInvalidateOnAnimation(this);
}
//}
mActivePointerId = INVALID_POINTER;
endDrag();
break;
不会有问题。但不知道会引起什么严重的问题
我只是把它贴在这里，以免其他人在评论中错过它。 Child of the NestedScrollView 上实现 OnClick 方法，更好的方法是在 xml 中为 child.
clickable=true
（使用与
<android.support.v4.widget.NestedScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<LinearLayout
android:id="@+id/content_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:clickable="true" > <!-- new -->
<!-- Page Content -->
</LinearLayout>
</android.support.v4.widget.NestedScrollView>