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"><TextViewandroid: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 {@Overrideprotected 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;@Overridepublic 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() {@Overridepublic 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).*/@UnsupportedAppUsageprivate 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,yint 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 viewevent.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。