有时候会遇到这种需求：本身控件显示在很小的范围内，但是要求扩大可点击的区域。根据官方文档https://developer.android.com/develop/ui/views/touch-and-input/gestures/viewgroup?hl=zh-cn#delegate可以得知通过 TouchDelegate 类，让父视图能够将子视图的可触摸区域扩展到子视图的边界之外。当子节点必须很小但需要更大的触摸区域时，这非常有用。
给个例子：
布局文件activity_main.xml如下：设置的TextView对应的宽和高都只有10dp
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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=".MainActivity">
<TextView
android:id="@+id/tv_test"
android:layout_width="10dp"
android:layout_height="10dp"
android:background="#e8e8e8"
android:gravity="center"
android:layout_centerInParent="true"
android:text="Hello World" />
</RelativeLayout>
对面的activity文件如下：
扩大textView对应的上下左右点击区域为500
● int paddingLeft = 500;
● int paddingRight = 500;
● int paddingTop = 500;
● int paddingBottom = 500;
package com.example.addview;
import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.TouchDelegate;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView testTextView = (TextView) findViewById(R.id.tv_test);
testTextView.setOnClickListener(new View.OnClickListener() {
int cnt = 0;
@Override
public void onClick(View v) {
cnt++;
Toast.makeText(MainActivity.this, "you clicked me" + " " + cnt + " times", Toast.LENGTH_SHORT).show();
}
});
final View parent = (View) testTextView.getParent();
int paddingLeft = 500;
int paddingRight = 500;
int paddingTop = 500;
int paddingBottom = 500;
testTextView.post(new Runnable() {
@Override
public void run() {
Rect bounds = new Rect();
testTextView.getHitRect(bounds);
bounds.left -= paddingLeft;
bounds.top -= paddingTop;
bounds.right += paddingRight;
bounds.bottom += paddingBottom;
TouchDelegate mTouchDelegate = new TouchDelegate(bounds,testTextView);
//设置parent的TouchDelegate,parent执行TouchDelegate的onTouchEvent方法会去调用代理的TextView的dispatchTouchEvent方法
parent.setTouchDelegate(mTouchDelegate);
}
});
}
}
然后截图就可以看到点击不是该控件显示的空白区域，也可以响应到该view的click事件。
总结：
通过PaddingLeft来扩大Android控件可点击区域的步骤如下：
● 首先，在 xml 文件中添加你的控件，并设置它的 paddingLeft 属性值。这个值应该设置为你希望扩大的像素值。
● 使用 TouchDelegate 类来创建一个代理对象，然后将它与控件绑定。代理对象告诉 Android 系统点击事件的触发范围。
● 然后使用 View.post 方法将扩大控件的宽度和高度的代码放在消息队列中。
那么为什么通过TouchDelegate类来创建的代理对象，与控件绑定以后可以扩大控件的宽度和高度呢？
从源码中可以看到如果设置了TouchDelegate，touchEvent会优先交给TouchDelegate来处理。
public class TouchDelegate {
/**
* View that should receive forwarded touch events
*/
private View mDelegateView;
/**
* Bounds in local coordinates of the containing view that should be mapped to the delegate
* view. This rect is used for initial hit testing.
*/
// 传入一个Rect对象
private Rect mBounds;
/**
* mBounds inflated to include some slop. This rect is to track whether the motion events
* should be considered to be within the delegate view.
*/
private Rect mSlopBounds;
/**
* True if the delegate had been targeted on a down event (intersected mBounds).
*/
@UnsupportedAppUsage
private boolean mDelegateTargeted;
/**
* The touchable region of the View extends above its actual extent.
*/
public static final int ABOVE = 1;
/**
* The touchable region of the View extends below its actual extent.
*/
public static final int BELOW = 2;
/**
* The touchable region of the View extends to the left of its actual extent.
*/
public static final int TO_LEFT = 4;
/**
* The touchable region of the View extends to the right of its actual extent.
*/
public static final int TO_RIGHT = 8;
private int mSlop;
/**
* Touch delegate information for accessibility
*/
private TouchDelegateInfo mTouchDelegateInfo;
/**
* Constructor
*
* @param bounds Bounds in local coordinates of the containing view that should be mapped to
* the delegate view
* @param delegateView The view that should receive motion events
*/
public TouchDelegate(Rect bounds, View delegateView) {
// 接收对应的view控件和扩大的区域
mBounds = bounds;
mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop();
mSlopBounds = new Rect(bounds);
mSlopBounds.inset(-mSlop, -mSlop);
mDelegateView = delegateView;
}
/**
* Forward touch events to the delegate view if the event is within the bounds
* specified in the constructor.
*
* @param event The touch event to forward
* @return True if the event was consumed by the delegate, false otherwise.
*/
public boolean onTouchEvent(@NonNull MotionEvent event) {
// 获取事件的坐标x,y
int x = (int)event.getX();
int y = (int)event.getY();
boolean sendToDelegate = false;
boolean hit = true;
boolean handled = false;
switch (event.getActionMasked()) {
// 如果是ACTION_DOWN事件，判断事件的位置x,y是否落在扩大的区域mBounds内
case MotionEvent.ACTION_DOWN:
mDelegateTargeted = mBounds.contains(x, y);
sendToDelegate = mDelegateTargeted;
break;
case MotionEvent.ACTION_POINTER_DOWN:
case MotionEvent.ACTION_POINTER_UP:
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
sendToDelegate = mDelegateTargeted;
if (sendToDelegate) {
Rect slopBounds = mSlopBounds;
if (!slopBounds.contains(x, y)) {
hit = false;
}
}
break;
case MotionEvent.ACTION_CANCEL:
sendToDelegate = mDelegateTargeted;
mDelegateTargeted = false;
break;
}
// 如果落在扩大的区域内
if (sendToDelegate) {
if (hit) {
// 设置该事件对应的触发位置
// Offset event coordinates to be inside the target view
event.setLocation(mDelegateView.getWidth() / 2, mDelegateView.getHeight() / 2);
} else {
// Offset event coordinates to be outside the target view (in case it does
// something like tracking pressed state)
int slop = mSlop;
event.setLocation(-(slop * 2), -(slop * 2));
}
// 拦截点击事件
handled = mDelegateView.dispatchTouchEvent(event);
}
return handled;
}
...
}
从源码中 可以看到，创建TouchDelegate 需要传入一个Rect(left,top,right,bottom) 和delegateView, onTouchEvent触发时，会通过这个Rect来判断点击事件是否落在区域内，如果是 则转发给代理view来处理该事件。
