自定义 View：ViewGroup 与 View 的事件传递

2021 年 11 月 18 日
本文字数：1814 字
阅读完需：约 6 分钟

1.知识点

ViewGroup.onInterceptTouchEvent 和 ViewGroup.onTouchEvent 两个接口的关系
上述两者与子 View.onTouchEvent 接口的关系
假设我们的布局如下所示：

<?xml version="1.0" encoding="utf-8"?><com.besmart.components.VirtualViewPager     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"    tools:context=".EmptyActivity">
    <com.besmart.components.TestView        android:background="#ff0000"        android:layout_width="match_parent"        android:layout_height="match_parent"/>            <View        android:background="#00ff00"        android:layout_width="match_parent"        android:layout_height="match_parent"/>
    <View        android:background="#0000ff"        android:layout_width="match_parent"        android:layout_height="match_parent"/>
</com.besmart.components.VirtualViewPager>

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2.原理

如上图所示，仅有当 onInterceptTouchEvent 返回 false 的时候，子 View 才有可能收到 onTouchEvent。
无论什么情况，onInterceptTouchEvent 总是会被调用，总可以接受到 ACTION_DOWN 事件
结合 ViewGroup.onInterceptTouchEvent 和 ViewGroup.onTouchEvent，可以在父控件处理触摸事件，同时不影响子 View 的触摸事件响应

3.代码

VirtualViewPager.java

package com.besmart.components;
import android.content.Context;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.view.ViewGroup;
public class VirtualViewPager extends ViewGroup {    private static final String TAG = "SimulatorViewPager";
    public VirtualViewPager(Context context, AttributeSet attrs) {        super(context, attrs);    }
    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        measureChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }
    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        int count = getChildCount();        Log.e(TAG, String.format("onLayout: 当前有几个子View %d-%d-%d-%d-%d", count, left, top, right, bottom));
        int childWidth = getWidth();        for (int i = 0; i < count; i++) {            View child = getChildAt(i);            child.layout(left, top, right, bottom);            left += childWidth;            right += childWidth;        }    }
    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.e(TAG, "onTouchEvent: "+event.toString());        return true;    }
    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        Log.e(TAG, "onInterceptTouchEvent: "+ev.toString());        boolean result = false;
        return result;    }}

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TestView.java

package com.besmart.components;
import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Path;import android.graphics.PathMeasure;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.View;
import androidx.annotation.Nullable;
import com.besmart.components.Util;
import java.util.Arrays;
public class TestView extends View {    public static final String TAG = "TestView";
    public TestView(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);    }
    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.e(TAG, "onTouchEvent: "+event.toString());        return true;    }}