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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。

自定义视图组

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
        ));
    }
}

主要活动

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>

当活动开始时onMeasure，onLayout和onDraw在标记为CustomVieGroup1和的视图组上被调用CustomVieGroup2。每个视图组在其子视图上调用这些方法。没关系。我明白了。

当我调用标记为 CustomVieGroup 1requestLayout的视图组时，在 CustomVieGroup 1上调用和调用。该小组在他们的孩子身上调用这些方法。我明白了。onMeasureonLayoutonDraw

当我调用requestLayout标记为 CustomVieGroup 2、和的视图组时onMeasure，在 CustomVieGroup 2上调用。该小组在他们的孩子身上调用这些方法。我也理解。onLayoutonDraw

但是当我requestLayout用 id 调用视图时，activity_main没有调用or 。为什么？我期望,并且会在两者上调用and （即带有 id 的视图的 cgildren ）onMeasureonLayoutCustomVieGroup1CustomVieGroup2onMeasureonLayoutonDrawCustomVieGroup1CustomVieGroup2activity_main

根据requestLayout 的文档：

这将安排视图树的布局传递。

4

1 回答 1

8

requestLayout()将导致(@id/activity_main) 的onLayout()方法LinearLayout执行。但是，不能保证该LinearLayout遗嘱随后会重新布局其子代；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，它的宽度和高度不会改变，因为它的大小是基于它的父大小，而不是它的孩子。因为它的布局不是基于它的孩子，所以没有必要LinearLayout重新布局它的孩子。这就是为什么使几乎任何ViewGroup大小与其父级匹配的布局无效不会导致该布局的子级被布局的原因。

您应该能够确认这会将您的LinearLayout(@id/activity_main) 更改为“wrap_content”。通过这样做，布局的大小将取决于其子级，因此需要重新布局其子级。这将导致调用您的自定义视图布局方法。希望这可以帮助，

于 2016-11-06T14:31:16.290 回答