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 Android教程網 >> Android技術 >> 關於Android編程 >> Android ViewGroup 事件分發機制詳解

Android ViewGroup 事件分發機制詳解

編輯：關於Android編程

今天給大家代碼ViewGroup事件分發的源碼解析~~凡是自定義ViewGroup實現各種滑動效果的，不可避免的會出現很多事件的沖突，對ViewGroup事件分發機制的了解，也有益於大家了解沖突產生的原因，以及對沖突進行處理~

1、案例

首先我們接著上一篇的代碼，在代碼中添加一個自定義的LinearLayout：

package com.example.zhy_event03;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.LinearLayout;

public class MyLinearLayout extends LinearLayout
{
	private static final String TAG = MyLinearLayout.class.getSimpleName();

	public MyLinearLayout(Context context, AttributeSet attrs)
	{
		super(context, attrs);
	}

	@Override
	public boolean dispatchTouchEvent(MotionEvent ev)
	{
		int action = ev.getAction();
		switch (action)
		{
		case MotionEvent.ACTION_DOWN:
			Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
			break;
		case MotionEvent.ACTION_MOVE:
			Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
			break;
		case MotionEvent.ACTION_UP:
			Log.e(TAG, "dispatchTouchEvent ACTION_UP");
			break;

		default:
			break;
		}
		return super.dispatchTouchEvent(ev);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event)
	{

		int action = event.getAction();

		switch (action)
		{
		case MotionEvent.ACTION_DOWN:
			Log.e(TAG, "onTouchEvent ACTION_DOWN");
			break;
		case MotionEvent.ACTION_MOVE:
			Log.e(TAG, "onTouchEvent ACTION_MOVE");
			break;
		case MotionEvent.ACTION_UP:
			Log.e(TAG, "onTouchEvent ACTION_UP");
			break;

		default:
			break;
		}

		return super.onTouchEvent(event);
	}

	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev)
	{

		int action = ev.getAction();
		switch (action)
		{
		case MotionEvent.ACTION_DOWN:
			Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN");
			break;
		case MotionEvent.ACTION_MOVE:
			Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE");
			break;
		case MotionEvent.ACTION_UP:
			Log.e(TAG, "onInterceptTouchEvent ACTION_UP");
			break;

		default:
			break;
		}

		return super.onInterceptTouchEvent(ev);
	}

	@Override
	public void requestDisallowInterceptTouchEvent(boolean disallowIntercept)
	{
		Log.e(TAG, "requestDisallowInterceptTouchEvent ");
		super.requestDisallowInterceptTouchEvent(disallowIntercept);
	}

}

繼承LinearLayout，然後復寫了與事件分發機制有關的代碼，添加上了日志的打印~

然後看我們的布局文件：

<com.example.zhy_event03.MyLinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <com.example.zhy_event03.MyButton
        android:id="@+id/id_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="click me" />

</com.example.zhy_event03.MyLinearLayout>

MyLinearLayout中包含一個MyButton，MyButton都上篇博客中已經出現過，這裡就不再貼代碼了，不清楚可以去查看~

然後MainActivity就是直接加載布局，沒有任何代碼~~~

直接運行我們的代碼，然後點擊我們的Button，依然是有意的MOVE一下，不然不會觸發MOVE事件，看一下日志的輸出：

09-06 09:57:27.287: E/MyLinearLayout(959): dispatchTouchEvent ACTION_DOWN
09-06 09:57:27.287: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_DOWN
09-06 09:57:27.287: E/MyButton(959): dispatchTouchEvent ACTION_DOWN
09-06 09:57:27.297: E/MyButton(959): onTouchEvent ACTION_DOWN
09-06 09:57:27.297: E/MyButton(959): onTouchEvent ACTION_MOVE
09-06 09:57:27.327: E/MyLinearLayout(959): dispatchTouchEvent ACTION_MOVE
09-06 09:57:27.327: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_MOVE
09-06 09:57:27.337: E/MyButton(959): dispatchTouchEvent ACTION_MOVE
09-06 09:57:27.337: E/MyButton(959): onTouchEvent ACTION_MOVE
09-06 09:57:27.457: E/MyLinearLayout(959): dispatchTouchEvent ACTION_UP
09-06 09:57:27.457: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_UP
09-06 09:57:27.457: E/MyButton(959): dispatchTouchEvent ACTION_UP
09-06 09:57:27.457: E/MyButton(959): onTouchEvent ACTION_UP

可以看到大體的事件流程為：

 

MyLinearLayout的dispatchTouchEvent -> MyLinearLayout的onInterceptTouchEvent -> MyButton的dispatchTouchEvent ->Mybutton的onTouchEvent

可以看出，在View上觸發事件，最先捕獲到事件的為View所在的ViewGroup，然後才會到View自身~

下面我們按照日志的輸出，進入源碼~

2、源碼分析

ViewGroup - dispatchTouchEvent

1、ViewGroup - dispatchTouchEvent – ACTION_DOWN

首先是ViewGroup的dispatchTouchEvent方法：

 @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (!onFilterTouchEventForSecurity(ev)) {
            return false;
        }

        final int action = ev.getAction();
        final float xf = ev.getX();
        final float yf = ev.getY();
        final float scrolledXFloat = xf + mScrollX;
        final float scrolledYFloat = yf + mScrollY;
        final Rect frame = mTempRect;

        boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;

        if (action == MotionEvent.ACTION_DOWN) {
            if (mMotionTarget != null) {
                // this is weird, we got a pen down, but we thought it was
                // already down!
                // XXX: We should probably send an ACTION_UP to the current
                // target.
                mMotionTarget = null;
            }
            // If we're disallowing intercept or if we're allowing and we didn't
            // intercept
            if (disallowIntercept || !onInterceptTouchEvent(ev)) {
                // reset this event's action (just to protect ourselves)
                ev.setAction(MotionEvent.ACTION_DOWN);
                // We know we want to dispatch the event down, find a child
                // who can handle it, start with the front-most child.
                final int scrolledXInt = (int) scrolledXFloat;
                final int scrolledYInt = (int) scrolledYFloat;
                final View[] children = mChildren;
                final int count = mChildrenCount;

                for (int i = count - 1; i >= 0; i--) {
                    final View child = children[i];
                    if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
                            || child.getAnimation() != null) {
                        child.getHitRect(frame);
                        if (frame.contains(scrolledXInt, scrolledYInt)) {
                            // offset the event to the view's coordinate system
                            final float xc = scrolledXFloat - child.mLeft;
                            final float yc = scrolledYFloat - child.mTop;
                            ev.setLocation(xc, yc);
                            child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
                            if (child.dispatchTouchEvent(ev))  {
                                // Event handled, we have a target now.
                                mMotionTarget = child;
                                return true;
                            }
                            // The event didn't get handled, try the next view.
                            // Don't reset the event's location, it's not
                            // necessary here.
                        }
                    }
                }
            }
        }                                                                                                                                                  ....//other code omitted

代碼比較長，決定分段貼出，首先貼出的是ACTION_DOWN事件相關的代碼。

16行：進入ACTION_DOWN的處理

17-23行：將mMotionTarget置為null

26行：進行判斷：if(disallowIntercept || !onInterceptTouchEvent(ev))

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