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Question

我正在尝试了解Android如何衡量和展示观点。我创建了一个包含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");
    }
}

CustomView

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中

<?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>

活动开始时，会在标记为onMeasure和onLayout的视图组上调用onDraw，CustomVieGroup1和CustomVieGroup2。每个视图组都会在其子项上调用这些方法。没关系。我明白了。

当我在标记为CustomVieGroup 1 的视图组上调用requestLayout时，会在CustomVieGroup 上调用onMeasure，onLayout和onDraw 1 即可。该小组将这些方法称为他们的孩子。我明白了。

当我在标记为CustomVieGroup 2 的视图组上调用requestLayout时，会在CustomVieGroup 上调用onMeasure，onLayout和onDraw 2 即可。该小组将这些方法称为他们的孩子。我也理解。

但是，如果我在ID为requestLayout的视图上致电activity_main，则onMeasure或onLayout不会调用CustomVieGroup1和CustomVieGroup2。为什么？我希望onMeasure，onLayout和onDraw都会在CustomVieGroup1和CustomVieGroup2上调用（即ID为activity_main的视图的cgildren ）

根据documentation of requestLayout：

  

这将安排视图树的布局传递。

Answer 1

requestLayout()将导致onLayout()（@ id / activity_main）的LinearLayout方法执行。但是，无法保证LinearLayout将重新布置其子女;这真的取决于它的实施。例如，您的LinearLayout宽度/高度设置为match_parent。当LinearLayout第二次布局时，其宽度和高度不会改变，因为它的大小取决于其父级大小，而不是其子级。由于其布局不基于其子项，因此LinearLayout无需重新布局其子项。这就是为什么使几乎与其父级匹配的任何ViewGroup的布局无效的原因不会导致该布局的子项被布局。

您应该能够确认这会将您的LinearLayout（@ id / activity_main）更改为＆＃39; wrap_content＆＃39;。通过这样做，布局的大小取决于其子项，因此需要重新布局其子项。这将导致调用自定义视图布局方法。希望这会有所帮助，