虽然网络上已经有非常多关于这个话题的优秀文章了，但还是写了这篇文章，主要还是为了加强自己的记忆吧，自己过一遍总比看别人的分析要深刻得多。那就走起吧。
简单演示样例
先看一个演示样例 :
布局文件 :
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center"
tools:context="com.example.touch_event.MainActivity"
tools:ignore="MergeRootFrame" >
<Button
android:id="@+id/my_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</FrameLayout>MainActivity文件:
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button mBtn = (Button) findViewById(R.id.my_button);
mBtn.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.d("", "### onTouch : " + event.getAction());
return false;
}
});
mBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Log.d("", "### onClick : " + v);
}
});
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.d("", "### activity dispatchTouchEvent");
return super.dispatchTouchEvent(ev);
}
} 当用户点击按钮时会输出例如以下Log, 08-31 03:03:56.116: D/(1560): ### activity dispatchTouchEvent
08-31 03:03:56.116: D/(1560): ### onTouch : 0
08-31 03:03:56.196: D/(1560): ### activity dispatchTouchEvent
08-31 03:03:56.196: D/(1560): ### onTouch : 1
08-31 03:03:56.196: D/(1560): ### onClick : android.widget.Button{52860d98 VFED..C. ...PH... 0,0-1080,144 #7f05003d app:id/my_button}
我们能够看到首先运行了Activity中的dispatchTouchEvent方法，然后运行了onTouch方法，然后再是dispatchTouchEvent --> onTouch， 最后才是运行按钮的点击事件。
这里我们可能有个疑问，为什么dispatchTouchEvent和onTouch都运行了两次。而onClick才运行了一次 ？ 为什么两次的Touch事件的action不一样，action 0 和 action 1究竟代表了什么 ？
覆写过onTouchEvent的朋友知道。一般来说我们在该方法体内都会处理集中touch类型的事件。有ACTION_DOWN、ACTION_MOVE、ACTION_UP等，只是上面我们的样例中并没有移动。仅仅是单纯的按下、抬起。
因此。我们的触摸事件也仅仅有按下、抬起，因此有2次touch事件，而action分别为0和1。我们看看MotionEvent中的一些变量定义吧:
public final class MotionEvent extends InputEvent implements Parcelable {
// 代码省略
public static final int ACTION_DOWN = 0; // 按下事件
public static final int ACTION_UP = 1; // 抬起事件
public static final int ACTION_MOVE = 2; // 手势移动事件
public static final int ACTION_CANCEL = 3; // 取消
// 代码省略
} 能够看到，代表按下的事件为0。抬起事件为1，也证实了我们上面所说的。在看另外一个场景:
1、我们在onTouch函数中返回true, 而且点击按钮，输出Log例如以下 :
08-31 03:06:04.764: D/(1612): ### activity dispatchTouchEvent 08-31 03:06:04.764: D/(1612): ### onTouch : 0 08-31 03:06:04.868: D/(1612): ### activity dispatchTouchEvent 08-31 03:06:04.868: D/(1612): ### onTouch : 1能够看到，按钮的点击事件并没有得到运行，为什么会这样呢 ？ 我们继续往下看吧。
Android Touch事件分发
那么整个事件分发的流程是如何的呢 ？
简单来说就是用户触摸手机屏幕会产生一个触摸消息，终于这个触摸消息会被传送到ViewRoot ( 看4.2的源代码时这个类改成了ViewRootImpl )的InputHandler。ViewRoot是GUI管理系统与GUI呈现系统之间的桥梁，依据ViewRoot的定义，发现它并非一个View类型。而是一个Handler。InputHandler是一个接口类型，用于处理KeyEvent和TouchEvent类型的事件，我们看看源代码 :
public final class ViewRoot extends Handler implements ViewParent,
View.AttachInfo.Callbacks {
// 代码省略
private final InputHandler mInputHandler = new InputHandler() {
public void handleKey(KeyEvent event, Runnable finishedCallback) {
startInputEvent(finishedCallback);
dispatchKey(event, true);
}
public void handleMotion(MotionEvent event, Runnable finishedCallback) {
startInputEvent(finishedCallback);
dispatchMotion(event, true); // 1、handle 触摸消息
}
};
// 代码省略
// 2、分发触摸消息
private void dispatchMotion(MotionEvent event, boolean sendDone) {
int source = event.getSource();
if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
dispatchPointer(event, sendDone); // 分发触摸消息
} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
dispatchTrackball(event, sendDone);
} else {
// TODO
Log.v(TAG, "Dropping unsupported motion event (unimplemented): " + event);
if (sendDone) {
finishInputEvent();
}
}
}
// 3、通过Handler投递消息
private void dispatchPointer(MotionEvent event, boolean sendDone) {
Message msg = obtainMessage(DISPATCH_POINTER);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
sendMessageAtTime(msg, event.getEventTime());
}
@Override
public void handleMessage(Message msg) { // ViewRoot覆写handlerMessage来处理各种消息
switch (msg.what) {
// 代码省略
case DO_TRAVERSAL:// 重绘整个View Tree的消息
if (mProfile) {
Debug.startMethodTracing("ViewRoot");
}
performTraversals();// 遍历整个View Tree。运行measure,layout,draw这几个过程.
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
break;
case DISPATCH_POINTER: { // 4、处理DISPATCH_POINTER类型的消息，即触摸屏幕的消息
MotionEvent event = (MotionEvent) msg.obj;
try {
deliverPointerEvent(event); // 5、处理触摸消息
} finally {
event.recycle();
if (msg.arg1 != 0) {
finishInputEvent();
}
if (LOCAL_LOGV || WATCH_POINTER) Log.i(TAG, "Done dispatching!");
}
} break;
// 代码省略
}
// 6、真正的处理事件
private void deliverPointerEvent(MotionEvent event) {
if (mTranslator != null) {
mTranslator.translateEventInScreenToAppWindow(event);
}
boolean handled;
if (mView != null && mAdded) {
// enter touch mode on the down
boolean isDown = event.getAction() == MotionEvent.ACTION_DOWN;
if (isDown) {
ensureTouchMode(true); // 假设是ACTION_DOWN事件则进入触摸模式。否则为按键模式。
}
if(Config.LOGV) {
captureMotionLog("captureDispatchPointer", event);
}
if (mCurScrollY != 0) {
event.offsetLocation(0, mCurScrollY); // 物理坐标向逻辑坐标的转换
}
if (MEASURE_LATENCY) {
lt.sample("A Dispatching TouchEvents", System.nanoTime() - event.getEventTimeNano());
}
// 7、分发事件。假设是窗体类型。则这里的mView相应的就是PhonwWindow中的DecorView，否则为根视图的ViewGroup。
handled = mView.dispatchTouchEvent(event);
// 8、假设终于事件没有被处理,且是ACTION_DOWN事件。那么就会交给mView，即DecorView类来处理.
if (!handled && isDown) {
int edgeSlop = mViewConfiguration.getScaledEdgeSlop();
final int edgeFlags = event.getEdgeFlags();
int direction = View.FOCUS_UP;
int x = (int)event.getX();
int y = (int)event.getY();
final int[] deltas = new int[2];
if ((edgeFlags & MotionEvent.EDGE_TOP) != 0) {
direction = View.FOCUS_DOWN;
if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {
deltas[0] = edgeSlop;
x += edgeSlop;
} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {
deltas[0] = -edgeSlop;
x -= edgeSlop;
}
} else if ((edgeFlags & MotionEvent.EDGE_BOTTOM) != 0) {
direction = View.FOCUS_UP;
if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {
deltas[0] = edgeSlop;
x += edgeSlop;
} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {
deltas[0] = -edgeSlop;
x -= edgeSlop;
}
} else if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {
direction = View.FOCUS_RIGHT;
} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {
direction = View.FOCUS_LEFT;
}
if (edgeFlags != 0 && mView instanceof ViewGroup) {
View nearest = FocusFinder.getInstance().findNearestTouchable(
((ViewGroup) mView), x, y, direction, deltas);
if (nearest != null) {
event.offsetLocation(deltas[0], deltas[1]);
event.setEdgeFlags(0);
// 看到,mView处理了该事件,也就是DecorView或者最顶级的ViewGroup.
mView.dispatchTouchEvent(event);
}
}
}
}
}
}
// 代码省略
}
经过层层迷雾。无论代码7处的mView是DecorView还是非窗体界面的根视图，其本质都是ViewGroup，即触摸事件终于被根视图ViewGroup进行分发。！！我们就以Activity为例来分析这个过程，我们知道显示出来的Activity有一个顶层窗体。这个窗体的实现类是PhoneWindow, PhoneWindow中的内容区域是一个DecorView类型的View，这个View这就是我们在手机上看到的内容，这个DecorView是FrameLayout的子类，Activity的的dispatchTouchEvent实际上就是调用PhoneWindow的dispatchTouchEvent。我们看看源代码吧，进入Activity的dispatchTouchEvent函数 :
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) { // 1、调用的是PhoneWindow的superDispatchTouchEvent(ev)
return true;
}
return onTouchEvent(ev);
}
public void onUserInteraction() {
} 能够看到，假设事件为按下事件，则会进入到onUserInteraction()这个函数，该函数为空实现，我们暂且无论它。继续看，发现touch事件的分发调用了getWindow().superDispatchTouchEvent(ev)函数。getWindow()获取到的实例的类型为PhoneWindow类型。你能够在你的Activity类中使用例如以下方式查看getWindow()获取到的类型：
Log.d("", "### Activiti中getWindow()获取的类型是 : " + this.getWindow()) ;输出:
08-31 03:40:17.036: D/(1688): ### Activiti中getWindow()获取的类型是 : com.android.internal.policy.impl.PhoneWindow@5287fe38OK，废话不多说。我们还是继续看PhoneWindow中的superDispatchTouchEvent函数吧。
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
} 恩，调用的是mDecor的superDispatchTouchEvent(event)函数，这个mDecor就是我们上面所说的DecorView类型，也就是我们看到的Activity上的全部内容的一个顶层ViewGroup，即整个ViewTree的根节点。看看它的声明吧。 // This is the top-level view of the window, containing the window decor.
private DecorView mDecor; DecorView
那么我继续看看DecorView究竟是个什么玩意儿吧。
private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
/* package */int mDefaultOpacity = PixelFormat.OPAQUE;
/** The feature ID of the panel, or -1 if this is the application's DecorView */
private final int mFeatureId;
private final Rect mDrawingBounds = new Rect();
private final Rect mBackgroundPadding = new Rect();
private final Rect mFramePadding = new Rect();
private final Rect mFrameOffsets = new Rect();
private boolean mChanging;
private Drawable mMenuBackground;
private boolean mWatchingForMenu;
private int mDownY;
public DecorView(Context context, int featureId) {
super(context);
mFeatureId = featureId;
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
final int keyCode = event.getKeyCode();
// 代码省略
return isDown ? PhoneWindow.this.onKeyDown(mFeatureId, event.getKeyCode(), event)
: PhoneWindow.this.onKeyUp(mFeatureId, event.getKeyCode(), event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Callback cb = getCallback();
return cb != null && mFeatureId < 0 ? cb.dispatchTouchEvent(ev) : super
.dispatchTouchEvent(ev);
}
@Override
public boolean dispatchTrackballEvent(MotionEvent ev) {
final Callback cb = getCallback();
return cb != null && mFeatureId < 0 ?
cb.dispatchTrackballEvent(ev) : super
.dispatchTrackballEvent(ev);
}
public boolean superDispatchKeyEvent(KeyEvent event) {
return super.dispatchKeyEvent(event);
}
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
public boolean superDispatchTrackballEvent(MotionEvent event) {
return super.dispatchTrackballEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
return onInterceptTouchEvent(event);
}
// 代码省略
}
能够看到，DecorView继承自FrameLayout， 它对于touch事件的分发( dispatchTouchEvent )、处理都是交给super类来处理。也就是FrameLayout来处理，我们在FrameLayout中没有看到相应的实现，那继续跟踪到FrameLayout的父类。即ViewGroup，我们看到了dispatchTouchEvent的实现，那我们就先看ViewGroup (Android 2.3 源代码)是如何进行事件分发的吧。
ViewGroup的Touch事件分发
/**
* {@inheritDoc}
*/
@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;
// 是否禁用拦截，假设为true表示不能拦截事件；反之，则为能够拦截事件
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
// ACTION_DOWN事件。即按下事件
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。假设不同意事件拦截或者不拦截该事件，那么运行以下的操作
if (disallowIntercept || !onInterceptTouchEvent(ev)) // 1、是否禁用拦截、是否拦截事件的推断
// 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--) // 2、迭代全部子view，查找触摸事件在哪个子view的坐标范围内
final View child = children[i];
// 该child是可见的
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
// 3、获取child的坐标范围
child.getHitRect(frame);
// 4、推断发生该事件坐标是否在该child坐标范围内
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;
// 5、child处理该事件，假设返回true，那么mMotionTarget为该child。正常情况下,
// dispatchTouchEvent(ev)的返回值即onTouchEcent的返回值。因此onTouchEcent假设返回为true，
// 那么mMotionTarget为触摸事件所在位置的child。
if (child.dispatchTouchEvent(ev))
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
}
}
}
}
}// end if
boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
(action == MotionEvent.ACTION_CANCEL);
if (isUpOrCancel) {
// Note, we've already copied the previous state to our local
// variable, so this takes effect on the next event
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
// The event wasn't an ACTION_DOWN, dispatch it to our target if
// we have one.
final View target = mMotionTarget;
// 6、假设mMotionTarget为空。那么运行super.super.dispatchTouchEvent(ev)，
// 即View.dispatchTouchEvent(ev),就是该View Group自己处理该touch事件，仅仅是又走了一遍View的分发过程而已.
// 拦截事件或者在不拦截事件且target view的onTouchEvent返回false的情况都会运行到这一步.
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
// if have a target, see if we're allowed to and want to intercept its
// events
// 7、假设没有禁用事件拦截。而且onInterceptTouchEvent(ev)返回为true，即进行事件拦截.
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
ev.setAction(MotionEvent.ACTION_CANCEL);
ev.setLocation(xc, yc);
//
if (!target.dispatchTouchEvent(ev)) {
// target didn't handle ACTION_CANCEL. not much we can do
// but they should have.
}
// clear the target
mMotionTarget = null;
// Don't dispatch this event to our own view, because we already
// saw it when intercepting; we just want to give the following
// event to the normal onTouchEvent().
return true;
}
if (isUpOrCancel) {
mMotionTarget = null;
}
// finally offset the event to the target's coordinate system and
// dispatch the event.
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc);
if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
mMotionTarget = null;
}
// 事件不拦截，且target view在ACTION_DOWN时返回true，那么兴许事件由target来处理事件
return target.dispatchTouchEvent(ev);
} 这个函数代码比較长，我们仅仅看上文中标注的几个关键点。首先在代码1处能够看到一个条件推断，假设
disallowIntercept和!onInterceptTouchEvent(ev)两者有一个为true。就会进入到这个条件推断中。disallowIntercept是指是否禁用掉事件拦截的功能，默认是false，也能够通过调用requestDisallowInterceptTouchEvent方法对这个值进行改动。那么当第一个值为false的时候就会全然依赖第二个值来决定能否够进入到条件推断的内部，第二个值是什么呢？onInterceptTouchEvent就是ViewGroup对事件进行拦截的一个函数。返回该函数返回false则表示不拦截事件。反之则表示拦截。第二个条件是是对onInterceptTouchEvent方法的返回值取反。也就是说假设我们在onInterceptTouchEvent方法中返回false。就会让第二个值为true。从而进入到条件推断的内部，假设我们在onInterceptTouchEvent方法中返回true，就会让第二个值的总体变为false，从而跳出了这个条件推断。比如我们须要实现ListView滑动删除某一项的功能。那么能够通过在onInterceptTouchEvent返回true,而且在onTouchEvent中实现相关的推断逻辑，从而实现该功能。
进入代码1内部的if后。有一个for循环。遍历了当前ViewGroup下的全部子child view。假设触摸该事件的坐标在某个child view的坐标范围内，那么该child view来处理这个触摸事件,即调用该child view的dispatchTouchEvent。
假设该child view是ViewGroup类型，那么继续运行上面的推断。而且遍历子view。假设该child view不是ViewGroup类型，那么直接调用的是View中的dispatchTouchEvent方法,除非这个child view的类型覆写了该方法。我们看看View中的dispatchTouchEvent函数：
View的Touch事件分发
/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
public boolean dispatchTouchEvent(MotionEvent event) {
if (!onFilterTouchEventForSecurity(event)) {
return false;
}
if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
mOnTouchListener.onTouch(this, event)) {
return true;
}
return onTouchEvent(event);
}
该函数中，首先推断该事件是否符合安全策略，然后推断该view是否是enable的 ，以及是否设置了Touch Listener，mOnTouchListener即我们通过setOnTouchListener设置的。
/**
* Register a callback to be invoked when a touch event is sent to this view.
* @param l the touch listener to attach to this view
*/
public void setOnTouchListener(OnTouchListener l) {
mOnTouchListener = l;
} 假设mOnTouchListener.onTouch(this, event)返回false则继续运行onTouchEvent(event)；假设mOnTouchListener.onTouch(this, event)返回true，则表示该事件被消费了，不再传递，因此也不会运行onTouchEvent(event)。这也验证了我们上文中留下的场景2。当onTouch函数返回true时，点击按钮，但我们的点击事件没有运行。那么我们还是先来看看onTouchEvent(event)函数究竟做了什么吧。 /**
* Implement this method to handle touch screen motion events.
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
final int viewFlags = mViewFlags;
if ((viewFlags & ENABLED_MASK) == DISABLED) // 1、推断该view是否enable
// 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)) // 2、是否是clickable或者long clickable
switch (event.getAction()) {
case MotionEvent.ACTION_UP: // 抬起事件
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(); // 获取焦点
}
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)) // post
performClick(); // 3、点击事件处理
}
}
}
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;
} 我们看到，在onTouchEvent函数中就是对ACTION_UP、ACTION_DOWN、ACTION_MOVE等几个事件进行处理。而最重要的就是UP事件了。由于这个里面包括了对用户点击事件的处理，或者是说对于用户而言相对重要一点，因此放在了第一个case中。在ACTION_UP事件中会推断该view是否enable、是否clickable、是否获取到了焦点。然后我们看到会通过post方法将一个PerformClick对象投递给UI线程。假设投递失败则直接调用performClick函数运行点击事件。
/**
* Causes the Runnable to be added to the message queue.
* The runnable will be run on the user interface thread.
*
* @param action The Runnable that will be executed.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public boolean post(Runnable action) {
Handler handler;
if (mAttachInfo != null) {
handler = mAttachInfo.mHandler;
} else {
// Assume that post will succeed later
ViewRoot.getRunQueue().post(action);
return true;
}
return handler.post(action);
}我们看看PerformClick类吧。
private final class PerformClick implements Runnable {
public void run() {
performClick();
}
} 能够看到，其内部就是包装了View类中的performClick()方法。再看performClick()方法： /**
* Register a callback to be invoked when this view is clicked. If this view is not
* clickable, it becomes clickable.
*
* @param l The callback that will run
*
* @see #setClickable(boolean)
*/
public void setOnClickListener(OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
mOnClickListener = l;
}
/**
* Call this view's OnClickListener, if it is defined.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
public boolean performClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
if (mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
mOnClickListener.onClick(this);
return true;
}
return false;
}
代码非常easy，主要就是调用了mOnClickListener.onClick(this);方法，即运行用户通过setOnClickListener设置进来的点击事件处理Listener。
总结
用户触摸屏幕产生一个触摸消息。系统底层将该消息转发给ViewRoot ( ViewRootImpl )，ViewRoot产生一个DISPATCHE_POINTER的消息，而且在handleMessage中处理该消息，终于会通过deliverPointerEvent(MotionEvent event)来处理该消息。
在该函数中会调用mView.dispatchTouchEvent(event)来分发消息,该mView是一个ViewGroup类型，因此是ViewGroup的dispatchTouchEvent(event)。在该函数中会遍历全部的child view，找到该事件的触发的左边与每一个child view的坐标进行对照，假设触摸的坐标在该child view的范围内，则由该child view进行处理。假设该child view是ViewGroup类型。则继续上一步的查找过程；否则运行View中的dispatchTouchEvent(event)函数。
在View的dispatchTouchEvent(event)中首先推断该控件是否enale以及mOnTouchListent是否为空，假设mOnTouchListener不为空则运行mOnTouchListener.onTouch(event)方法，假设该方法返回false则再运行View中的onTouchEvent(event)方法，而且在该方法中运行mOnClickListener.onClick(this, event) ;方法。 假设mOnTouchListener.onTouch(event)返回true则不会运行onTouchEvent方法，因此点击事件也不会被运行。
粗略的流程图例如以下 :
