android 事件分发机制

1.View的事件分发机制

一个button，简单一点就是onTouch，还有onclick事件，我们一个一个来分析

首先响应的是dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent event) {
    if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
            mOnTouchListener.onTouch(this, event)) {
        return true;
    }
    return onTouchEvent(event);
}

其实，在android源码的命名还是很有规律的，dispatchXXX，也就是分发机制，往往就是第一个需要响应的地方。

我们来分析下：touchlistener不为空，也就是view的使用者设置了回调。

第二个条件就是View必须是enable的。第三：onTouch返回false，就说明onTouch不消费该事件，由OnTouchEvent响应。

如果返回True，那么就会直接return。

所以onClick事件一定会被调到。

public boolean onTouchEvent(MotionEvent event) {
    final int viewFlags = mViewFlags;
    if ((viewFlags & ENABLED_MASK) == DISABLED) {
        // A disabled view that is clickable still consumes the touch
        // events, it just doesn't respond to them.
        return (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));
    }
    if (mTouchDelegate != null) {
        if (mTouchDelegate.onTouchEvent(event)) {
            return true;
        }
    }
    if (((viewFlags & CLICKABLE) == CLICKABLE ||
            (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_UP:
                boolean prepressed = (mPrivateFlags & PREPRESSED) != 0;
                if ((mPrivateFlags & PRESSED) != 0 || prepressed) {
                    // take focus if we don't have it already and we should in
                    // touch mode.
                    boolean focusTaken = false;
                    if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                        focusTaken = requestFocus();
                    }
                    if (!mHasPerformedLongPress) {
                        // This is a tap, so remove the longpress check
                        removeLongPressCallback();
                        // Only perform take click actions if we were in the pressed state
                        if (!focusTaken) {
                            // Use a Runnable and post this rather than calling
                            // performClick directly. This lets other visual state
                            // of the view update before click actions start.
                            if (mPerformClick == null) {
                                mPerformClick = new PerformClick();
                            }
                            if (!post(mPerformClick)) {
                                performClick();
                            }
                        }
                    }
                    if (mUnsetPressedState == null) {
                        mUnsetPressedState = new UnsetPressedState();
                    }
                    if (prepressed) {
                        mPrivateFlags |= PRESSED;
                        refreshDrawableState();
                        postDelayed(mUnsetPressedState,
                                ViewConfiguration.getPressedStateDuration());
                    } else if (!post(mUnsetPressedState)) {
                        // If the post failed, unpress right now
                        mUnsetPressedState.run();
                    }
                    removeTapCallback();
                }
                break;
            case MotionEvent.ACTION_DOWN:
                if (mPendingCheckForTap == null) {
                    mPendingCheckForTap = new CheckForTap();
                }
                mPrivateFlags |= PREPRESSED;
                mHasPerformedLongPress = false;
                postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                break;
            case MotionEvent.ACTION_CANCEL:
                mPrivateFlags &= ~PRESSED;
                refreshDrawableState();
                removeTapCallback();
                break;
            case MotionEvent.ACTION_MOVE:
                final int x = (int) event.getX();
                final int y = (int) event.getY();
                // Be lenient about moving outside of buttons
                int slop = mTouchSlop;
                if ((x < 0 - slop) || (x >= getWidth() + slop) ||
                        (y < 0 - slop) || (y >= getHeight() + slop)) {
                    // Outside button
                    removeTapCallback();
                    if ((mPrivateFlags & PRESSED) != 0) {
                        // Remove any future long press/tap checks
                        removeLongPressCallback();
                        // Need to switch from pressed to not pressed
                        mPrivateFlags &= ~PRESSED;
                        refreshDrawableState();
                    }
                }
                break;
        }
        return true;
    }
    return false;
}  

onTouchEvent

最终会走到performClick这个方法。

    public boolean performClick() {
        final boolean result;
        final ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnClickListener != null) {
            playSoundEffect(SoundEffectConstants.CLICK);
            li.mOnClickListener.onClick(this);
            result = true;
        } else {
            result = false;
        }

        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
        return result;
    }

可以看到，如果setOnClickListener, onClick 就会走到。

2.ViewGroup的事件分发机制

<com.joyfulmath.frameworksample.viewdemo.MyLayout
        android:id="@+id/my_layout"
        android:background="#99000044"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <Button
            android:id="@+id/button_id"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="button"/>
        <Button
            android:id="@+id/imageId"
            android:layout_centerInParent="true"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@android:drawable/ic_lock_power_off"/>
    </com.joyfulmath.frameworksample.viewdemo.MyLayout>

一个layout里面有2个button，

package com.joyfulmath.frameworksample.viewdemo;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ImageView;

import com.joyfulmath.frameworksample.R;

/**
 * Created by Administrator on 2016/8/27 0027.
 */
public class TestViewAction extends Activity implements View.OnClickListener,View.OnTouchListener
{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_main);
        Button button = (Button) findViewById(R.id.button_id);
        button.setOnClickListener(this);
        button.setOnTouchListener(this);
        Button imageView = (Button) findViewById(R.id.imageId);
        imageView.setOnClickListener(this);
        imageView.setOnTouchListener(this);
        MyLayout myLayout = (MyLayout) findViewById(R.id.my_layout);
        myLayout.setOnTouchListener(this);
        myLayout.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId())
        {
            case R.id.button_id:
                TraceLog.i("button_id");
                break;
            case R.id.imageId:
                TraceLog.i("imageId");
                break;
            case R.id.my_layout:
                TraceLog.i("my_layout");
                break;
        }

    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (v.getId())
        {
            case R.id.button_id:
                TraceLog.i("button_id");
                break;
            case R.id.imageId:
                TraceLog.i("imageId");
                break;
            case R.id.my_layout:
                TraceLog.i("my_layout");
                break;
        }
        return false;
    }
}

TestViewAction

分别点击button1 & button2 & 灰色部分

等到log如下：

08-27 10:19:26.799 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: button_id [at (TestViewAction.java:55)]
08-27 10:19:26.880 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: button_id [at (TestViewAction.java:55)]
08-27 10:19:26.896 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: button_id [at (TestViewAction.java:55)]
08-27 10:19:26.913 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: button_id [at (TestViewAction.java:55)]
08-27 10:19:26.926 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: button_id [at (TestViewAction.java:55)]
08-27 10:19:26.926 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onClick: button_id [at (TestViewAction.java:38)]
08-27 10:19:27.434 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: imageId [at (TestViewAction.java:58)]
08-27 10:19:27.535 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: imageId [at (TestViewAction.java:58)]
08-27 10:19:27.543 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: imageId [at (TestViewAction.java:58)]
08-27 10:19:27.544 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onClick: imageId [at (TestViewAction.java:41)]
08-27 10:19:28.111 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: my_layout [at (TestViewAction.java:61)]
08-27 10:19:28.156 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: my_layout [at (TestViewAction.java:61)]
08-27 10:19:28.173 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: my_layout [at (TestViewAction.java:61)]
08-27 10:19:28.190 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: my_layout [at (TestViewAction.java:61)]
08-27 10:19:28.237 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onTouch: my_layout [at (TestViewAction.java:61)]
08-27 10:19:28.237 2120-2120/com.joyfulmath.frameworksample I/TestViewAction: onClick: my_layout [at (TestViewAction.java:44)]

也就是点击button1以后，不会传递都layout

But，如果layout里面有一个函数

public boolean onInterceptTouchEvent(MotionEvent ev)

这个函数就是截断对button的分发处理，默认是return false。

至此，我们有了一个大概的流程。

Activtiy->ViewGroup->View

如果仔细分析就会发现，在Activity里面有一个getDocView。所以Activity里面有个RootView的概念。

言归正传，ViewGroup本质上也是一个View，所以，可以把模型简单的定性为Activtiy->ViewGroup->View 三层。

首先Activity里面有2个函数，我们分析看看：

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        TraceLog.i();
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        TraceLog.i();
        return super.onTouchEvent(event);
    }

所以大体流程如下：

1.@Activty.diapatchTouchEvent ->@Layout.dispatchTouchEvent->@layout.onInterceptTouchEvent return true/false

2.return true->@layout.onTouchEvent 后面部分同view

3.return false->@view.dispatchTouchEvent View的分发见上一片流程。

上面是2016年的文章分析，最新的java层的分析可以参考如下文章

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参考：

《深入理解android设计思想》   林学森