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;
}
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;
}
}
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。
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