padding方式

适合图片等dp或px为单位的view，

不适合textview、button这种以或含sp计算单位的view。

TouchDelegate方式

作用

假设有两个View，分别是v1、v2，可以通过v1.setTouchDelegate(new TouchDelegate(bounds, v2))来委派触摸事件，其中bounds是一个Rect。执行该这个方法后，v1中bounds区域的触摸事件TouchEvent将会传递给v2。

实现API

/**
     * 扩展点击区域的范围
     *
     * @param view       需要扩展的元素，此元素必需要有父级元素
     * @param expendSize 需要扩展的尺寸
     */
    private fun expendTouchArea(view: View?, expendSize: Int) {
        expendTouchArea(view, expendSize, expendSize, expendSize, expendSize)
    }

    private fun expendTouchArea(view: View?, left: Int, top: Int, right: Int, bottom: Int) {
        if (view == null) {
            return
        }

        val parentView = view.parent as View
        parentView.post {
            val rect = Rect()
            view.getHitRect(rect) // 如果太早执行本函数，会获取rect失败，因为此时UI界面尚未开始绘制，无法获得正确的坐标
            rect.left -= left
            rect.top -= top
            rect.right += right
            rect.bottom += bottom
            parentView.touchDelegate = TouchDelegate(rect, view)
        }
    }

实现介绍

在Android的UI开发中，经常遇到部分控件UI过小 对用户来说不好点击，此时 我们可能通过在外部包裹一层FrameLayout或者是给控件设置padding的方式来扩大 控件的区域大小。

事实是，在系统已经提供了扩大控件点击区域判断范围的代理方式，我们看下View类的源码

class View {
    /**
     * The delegate to handle touch events that are physically in this view
     * but should be handled by another view.
     */
    private TouchDelegate mTouchDelegate = null;

	public boolean onTouchEvent(MotionEvent event) {
		//...
		
		if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }
	}
    /**
     * Sets the TouchDelegate for this View.
     */
    public void setTouchDelegate(TouchDelegate delegate) {
        mTouchDelegate = delegate;
    }
}

从源码中可以看到如果设置了TouchDelegate，touchEvent会优先交给TouchDelegate来处理。

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.view;

import android.graphics.Rect;

/**
 * Helper class to handle situations where you want a view to have a larger touch area than its
 * actual view bounds. The view whose touch area is changed is called the delegate view. This
 * class should be used by an ancestor of the delegate. To use a TouchDelegate, first create an
 * instance that specifies the bounds that should be mapped to the delegate and the delegate
 * view itself.
 * <p>
 * The ancestor should then forward all of its touch events received in its
 * {@link android.view.View#onTouchEvent(MotionEvent)} to {@link #onTouchEvent(MotionEvent)}.
 * </p>
 */
public class TouchDelegate {

    /**

    private View mDelegateView;

    private Rect mBounds;

    private boolean mDelegateTargeted;

    public TouchDelegate(Rect bounds, View delegateView) {
        mBounds = bounds;

        mDelegateView = delegateView;
    }

    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        boolean sendToDelegate = false;
        boolean hit = true;
        boolean handled = false;

        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                mDelegateTargeted = mBounds.contains(x, y);
                sendToDelegate = mDelegateTargeted;
                break;
                //...
        }
        if (sendToDelegate) {
            final View delegateView = mDelegateView;

            if (hit) {
                // Offset event coordinates to be inside the target view
                event.setLocation(delegateView.getWidth() / 2, delegateView.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));
            }
            handled = delegateView.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。

但这个自定义的View并不是完美的，还存在以下问题：

1. 必须保证parent足够大，如果自定义的范围超出parent的大小，则超出的那部分无效。
2. 一个parent只能设置一个触摸委派，设置多个时，只有最后设置的child有效。如果希望一个view能设置多个委派，需要再自定义parent

总而言之，要触发委派，必须保证parent接收到了触摸事件，并且落在了你定义的范围内。