android 扩大view的响应区域

1.Android提供TouchDelegate帮助实现扩大一个很小的view的点击区域

例如：https://developer.android.com/training/gestures/viewgroup.html#delegate

布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/parent_layout"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context=".MainActivity" >
 
     <ImageButton android:id="@+id/button"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:background="@null"
          android:src="@drawable/icon" />
</RelativeLayout>

代码

// Get the parent view
        View parentView = findViewById(R.id.parent_layout);
 
        parentView.post(new Runnable() {
            // Post in the parent's message queue to make sure the parent
            // lays out its children before you call getHitRect()
            @Override
            public void run() {
                // The bounds for the delegate view (an ImageButton
                // in this example)
                Rect delegateArea = new Rect();
                ImageButton myButton = (ImageButton) findViewById(R.id.button);
                myButton.setEnabled(true);
                myButton.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Toast.makeText(MainActivity.this,
                                "Touch occurred within ImageButton touch region.",
                                Toast.LENGTH_SHORT).show();
                    }
                });
 
                // The hit rectangle for the ImageButton
                myButton.getHitRect(delegateArea);
 
                // Extend the touch area of the ImageButton beyond its bounds
                // on the right and bottom.
                delegateArea.right += 100;
                delegateArea.bottom += 100;
 
                // Instantiate a TouchDelegate.
                // "delegateArea" is the bounds in local coordinates of
                // the containing view to be mapped to the delegate view.
                // "myButton" is the child view that should receive motion
                // events.
                TouchDelegate touchDelegate = new TouchDelegate(delegateArea,
                        myButton);
 
                // Sets the TouchDelegate on the parent view, such that touches
                // within the touch delegate bounds are routed to the child.
                if (View.class.isInstance(myButton.getParent())) {
                    ((View) myButton.getParent()).setTouchDelegate(touchDelegate);
                }
            }
        });

简单解释

1. 获取parentView并且在UIThread上post一个Runnable,确保viewGroup在绘制子view之前得到子view的getHintRect(),getHintRect()返回就是该view在viewGroup中的点击区域

2.Find这个View,并且通过getHintRect()得到点击区域,rect

3.扩大点击范围即扩大rect的left,right,top,bottom

4.初始化TouchDelegate,并且将扩大后的rect和view对象作为参数传入

5.在viewGroup中设置touchDelegate，viewGroup会自动扩大该view的响应区域