child 视图的 onMeasure 和 onLayout 在其 parent 上的 requestLayout 之后未被调用
onMeasure and onLayout of child views are not called after requestLayout on their parent
我正在尝试了解 Android 如何测量和布置视图。我创建了一个带有自定义视图和视图组的示例应用程序。
CustomViewGroup
public class CustomViewGroup extends ViewGroup {
private static final String LOG_TAG = "CustomViewGroup";
public CustomViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onMeasure(widthMeasureSpec=%d, heightMeasureSpec%d)",
widthMeasureSpec, heightMeasureSpec
));
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
// Make or work out measurements for children here (MeasureSpec.make...)
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onLayout(changed=%b, left=%d, top=%d, right=%d, bottom=%d)",
changed, left, top, top, right, bottom
));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d(LOG_TAG, getTag() + " " + "onDraw");
}
}
自定义视图
public class CustomView extends View {
private static final String LOG_TAG = "CustomView";
public CustomView(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onLayout(changed=%b, left=%d, top=%d, right=%d, bottom=%d)",
changed, left, top, top, right, bottom
));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d(LOG_TAG, getTag() + " " +"onDraw");
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onMeasure(widthMeasureSpec=%d, heightMeasureSpec=%d)",
widthMeasureSpec, heightMeasureSpec
));
}
}
MainActivity
public class MainActivity extends AppCompatActivity {
private View mCustomGroup1;
private View mCustomGroup2;
private View mContainer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d("MainAct", "onCreate");
mCustomGroup1 = findViewById(R.id.requestLayout);
mCustomGroup2 = findViewById(R.id.requestLayout2);
mContainer = findViewById(R.id.activity_main);
findViewById(R.id.requestLayoutBtn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCustomGroup1.requestLayout();
}
});
findViewById(R.id.requestLayoutBtn2).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCustomGroup2.requestLayout();
}
});
findViewById(R.id.requestLayoutContBtn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mContainer.requestLayout();
}
});
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
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="ru.dmitriev.squareorderedlayout.MainActivity">
<Button
android:id="@+id/requestLayoutBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayout" />
<Button
android:id="@+id/requestLayoutBtn2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayout2" />
<Button
android:id="@+id/requestLayoutContBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayoutCont" />
<ru.dmitriev.squareorderedlayout.CustomViewGroup
android:id="@+id/requestLayout"
android:layout_width="100dp"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#7f7"
android:tag="CustomVieGroup1">
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView11" />
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView12" />
</ru.dmitriev.squareorderedlayout.CustomViewGroup>
<ru.dmitriev.squareorderedlayout.CustomViewGroup
android:id="@+id/requestLayout2"
android:layout_width="100dp"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#f77"
android:tag="CustomVieGroup2">
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView21" />
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView22" />
</ru.dmitriev.squareorderedlayout.CustomViewGroup>
</LinearLayout>
当 activity 启动时，在标记为 CustomVieGroup1 和 CustomVieGroup2 的视图组上调用 onMeasure、onLayout 和 onDraw。每个视图组在其 children 上调用这些方法。没关系。我明白了。
当我在标记为 CustomVieGroup 的视图组上调用 requestLayout 时 1、onMeasure、onLayout 和 onDraw 被调用在 CustomVieGroup1 上。该小组在 children 上调用这些方法。我明白了。
当我在标记为 CustomVieGroup 的视图组上调用 requestLayout 时 2、onMeasure、onLayout 和 onDraw 被调用在 CustomVieGroup2 上。该小组在 children 上调用这些方法。我也明白了。
但是当我在 ID 为 activity_main 的视图上调用 requestLayout 时，onMeasure 和 onLayout 不会在 CustomVieGroup1 或 [=20= 上调用].为什么？我预计 onMeasure、onLayout 和 onDraw 将在 CustomVieGroup1 和 CustomVieGroup2 上被调用（即具有 id activity_main 的视图的 cgildren )
根据 documentation of requestLayout:
This will schedule a layout pass of the view tree.
requestLayout() 将导致 LinearLayout (@id/activity_main) 的 onLayout() 方法执行。但是，不能保证 LinearLayout 会 re-layout 其 children；这真的取决于它的实施。例如，您的 LinearLayout width/height 设置为 match_parent。当 LinearLayout 第二次变为 laid-out 时，它的宽度和高度不会改变，因为它的大小是基于它的 parent 大小，而不是它的 children。因为它的布局不是基于它的children，所以不需要LinearLayout到re-layout它的children。这就是为什么使几乎任何大小与其 parent 匹配的 ViewGroup 的布局无效不会导致该布局的 children 成为 laid-out.
您应该能够确认这是将您的 LinearLayout (@id/activity_main) 更改为 'wrap_content'。通过这样做，布局的大小变得取决于它的 children，因此它需要 re-layout 它的 children。这将导致您的自定义视图布局方法被调用。希望这有帮助，
我正在尝试了解 Android 如何测量和布置视图。我创建了一个带有自定义视图和视图组的示例应用程序。
CustomViewGroup
public class CustomViewGroup extends ViewGroup {
private static final String LOG_TAG = "CustomViewGroup";
public CustomViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onMeasure(widthMeasureSpec=%d, heightMeasureSpec%d)",
widthMeasureSpec, heightMeasureSpec
));
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
// Make or work out measurements for children here (MeasureSpec.make...)
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onLayout(changed=%b, left=%d, top=%d, right=%d, bottom=%d)",
changed, left, top, top, right, bottom
));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d(LOG_TAG, getTag() + " " + "onDraw");
}
}
自定义视图
public class CustomView extends View {
private static final String LOG_TAG = "CustomView";
public CustomView(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onLayout(changed=%b, left=%d, top=%d, right=%d, bottom=%d)",
changed, left, top, top, right, bottom
));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d(LOG_TAG, getTag() + " " +"onDraw");
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(LOG_TAG, String.format(Locale.ENGLISH,
getTag() + " " +
"onMeasure(widthMeasureSpec=%d, heightMeasureSpec=%d)",
widthMeasureSpec, heightMeasureSpec
));
}
}
MainActivity
public class MainActivity extends AppCompatActivity {
private View mCustomGroup1;
private View mCustomGroup2;
private View mContainer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d("MainAct", "onCreate");
mCustomGroup1 = findViewById(R.id.requestLayout);
mCustomGroup2 = findViewById(R.id.requestLayout2);
mContainer = findViewById(R.id.activity_main);
findViewById(R.id.requestLayoutBtn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCustomGroup1.requestLayout();
}
});
findViewById(R.id.requestLayoutBtn2).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCustomGroup2.requestLayout();
}
});
findViewById(R.id.requestLayoutContBtn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mContainer.requestLayout();
}
});
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
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="ru.dmitriev.squareorderedlayout.MainActivity">
<Button
android:id="@+id/requestLayoutBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayout" />
<Button
android:id="@+id/requestLayoutBtn2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayout2" />
<Button
android:id="@+id/requestLayoutContBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="requestLayoutCont" />
<ru.dmitriev.squareorderedlayout.CustomViewGroup
android:id="@+id/requestLayout"
android:layout_width="100dp"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#7f7"
android:tag="CustomVieGroup1">
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView11" />
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView12" />
</ru.dmitriev.squareorderedlayout.CustomViewGroup>
<ru.dmitriev.squareorderedlayout.CustomViewGroup
android:id="@+id/requestLayout2"
android:layout_width="100dp"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#f77"
android:tag="CustomVieGroup2">
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView21" />
<ru.dmitriev.squareorderedlayout.CustomView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="CustomView22" />
</ru.dmitriev.squareorderedlayout.CustomViewGroup>
</LinearLayout>
当 activity 启动时，在标记为 CustomVieGroup1 和 CustomVieGroup2 的视图组上调用 onMeasure、onLayout 和 onDraw。每个视图组在其 children 上调用这些方法。没关系。我明白了。
当我在标记为 CustomVieGroup 的视图组上调用 requestLayout 时 1、onMeasure、onLayout 和 onDraw 被调用在 CustomVieGroup1 上。该小组在 children 上调用这些方法。我明白了。
当我在标记为 CustomVieGroup 的视图组上调用 requestLayout 时 2、onMeasure、onLayout 和 onDraw 被调用在 CustomVieGroup2 上。该小组在 children 上调用这些方法。我也明白了。
但是当我在 ID 为 activity_main 的视图上调用 requestLayout 时，onMeasure 和 onLayout 不会在 CustomVieGroup1 或 [=20= 上调用].为什么？我预计 onMeasure、onLayout 和 onDraw 将在 CustomVieGroup1 和 CustomVieGroup2 上被调用（即具有 id activity_main 的视图的 cgildren )
根据 documentation of requestLayout:
This will schedule a layout pass of the view tree.
requestLayout() 将导致 LinearLayout (@id/activity_main) 的 onLayout() 方法执行。但是，不能保证 LinearLayout 会 re-layout 其 children；这真的取决于它的实施。例如，您的 LinearLayout width/height 设置为 match_parent。当 LinearLayout 第二次变为 laid-out 时，它的宽度和高度不会改变，因为它的大小是基于它的 parent 大小，而不是它的 children。因为它的布局不是基于它的children，所以不需要LinearLayout到re-layout它的children。这就是为什么使几乎任何大小与其 parent 匹配的 ViewGroup 的布局无效不会导致该布局的 children 成为 laid-out.
您应该能够确认这是将您的 LinearLayout (@id/activity_main) 更改为 'wrap_content'。通过这样做，布局的大小变得取决于它的 children，因此它需要 re-layout 它的 children。这将导致您的自定义视图布局方法被调用。希望这有帮助，