我正在尝试了解 Android 如何测量和布局 View 。我创建了一个带有自定义 View 和 View 组的示例应用。
自定义 View 组
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 View
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
));
}
}
主 Activity
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 开始时,onMeasure
、onLayout
和 onDraw
将在标记为 CustomVieGroup1
的 View 组上调用,并且CustomVieGroup2
。每个 View 组在其 subview 上调用这些方法。没关系。我明白了。
当我在标记为 CustomVieGroup1、onMeasure
、onLayout
和 的 View 组上调用
在 CustomVieGroup1 上调用。该小组将这些方法用于他们的 child 。我明白了。requestLayout
时onDraw
当我在标记为 CustomVieGroup2、onMeasure
、onLayout
和 的 View 组上调用
在 CustomVieGroup2 上调用。该小组将这些方法用于他们的 child 。我也明白。requestLayout
时onDraw
但是,当我在 ID 为 activity_main
的 View 上调用 requestLayout
时,不会调用 onMeasure
和 onLayout
CustomVieGroup1
或 CustomVieGroup2
。为什么?我预计 onMeasure
、onLayout
和 onDraw
将在 CustomVieGroup1
和 CustomVieGroup2
上被调用>(即 id 为 activity_main
的 View 的 cgildren)
根据documentation of requestLayout :
This will schedule a layout pass of the view tree.
最佳答案
requestLayout()
将导致 LinearLayout
(@id/activity_main) 的 onLayout()
方法执行。但是,无法保证 LinearLayout
会重新布局其子项;这真的取决于它的实现。例如,您的 LinearLayout
宽度/高度设置为 match_parent
。当 LinearLayout
被第二次布局时,它的宽度和高度不会改变,因为它的大小是基于父元素的大小,而不是它的子元素。因为它的布局不是基于它的子元素,所以 LinearLayout
不需要重新布局它的子元素。这就是为什么几乎所有大小与其父级匹配的 ViewGroup
的布局无效都不会导致该布局的子级被布局。
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,布局的大小变得依赖于它的 child ,所以它需要重新布局它的 child 。这将导致您的自定义 View 布局方法被调用。希望这有帮助,
关于android - subview 的 onMeasure 和 onLayout 不会在其父 View 的 requestLayout 之后调用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40450321/