Android Touch事件分發(fā)過程詳解
本文以實(shí)例形式講述了Android Touch事件分發(fā)過程,對(duì)于深入理解與掌握Android程序設(shè)計(jì)有很大的幫助作用。具體分析如下:
首先,從一個(gè)簡(jiǎn)單示例入手:
先看一個(gè)示例如下圖所示:
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); } }
當(dāng)用戶點(diǎn)擊按鈕時(shí)會(huì)輸出如下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}
我們可以看到首先執(zhí)行了Activity中的dispatchTouchEvent方法,然后執(zhí)行了onTouch方法,然后再是dispatchTouchEvent --> onTouch, 最后才是執(zhí)行按鈕的點(diǎn)擊事件。這里我們可能有個(gè)疑問,為什么dispatchTouchEvent和onTouch都執(zhí)行了兩次,而onClick才執(zhí)行了一次 ? 為什么兩次的Touch事件的action不一樣,action 0 和 action 1到底代表了什么 ?
覆寫過onTouchEvent的朋友知道,一般來說我們?cè)谠摲椒w內(nèi)都會(huì)處理集中touch類型的事件,有ACTION_DOWN、ACTION_MOVE、ACTION_UP等,不過上面我們的例子中并沒有移動(dòng),只是單純的按下、抬起。因此,我們的觸摸事件也只有按下、抬起,因此有2次touch事件,而action分別為0和1。我們看看MotionEvent中的一些變量定義吧:
public final class MotionEvent extends InputEvent implements Parcelable { // 代碼省略 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; // 手勢(shì)移動(dòng)事件 public static final int ACTION_CANCEL = 3; // 取消 // 代碼省略 }
可以看到,代表按下的事件為0,抬起事件為1,也證實(shí)了我們上面所說的。
在看另外兩個(gè)場(chǎng)景:
1、我們點(diǎn)擊按鈕外的區(qū)域,輸出Log如下 :
08-31 03:04:45.408: D/(1560): ### activity dispatchTouchEvent08-31 03:04:45.512: D/(1560): ### activity dispatchTouchEvent
2、我們?cè)趏nTouch函數(shù)中返回true, 輸出Log如下 :
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
以上兩個(gè)場(chǎng)景為什么會(huì)這樣呢 ? 我們繼續(xù)往下看吧。
Android Touch事件分發(fā)
那么整個(gè)事件分發(fā)的流程是怎樣的呢 ?
簡(jiǎn)單來說就是用戶觸摸手機(jī)屏幕會(huì)產(chǎn)生一個(gè)觸摸消息,最終這個(gè)觸摸消息會(huì)被傳送到ViewRoot ( 看4.2的源碼時(shí)這個(gè)類改成了ViewRootImpl )的InputHandler,ViewRoot是GUI管理系統(tǒng)與GUI呈現(xiàn)系統(tǒng)之間的橋梁,根據(jù)ViewRoot的定義,發(fā)現(xiàn)它并不是一個(gè)View類型,而是一個(gè)Handler。InputHandler是一個(gè)接口類型,用于處理KeyEvent和TouchEvent類型的事件,我們看看源碼 :
public final class ViewRoot extends Handler implements ViewParent, View.AttachInfo.Callbacks { // 代碼省略 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 觸摸消息 } }; // 代碼省略 // 2、分發(fā)觸摸消息 private void dispatchMotion(MotionEvent event, boolean sendDone) { int source = event.getSource(); if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) { dispatchPointer(event, sendDone); // 分發(fā)觸摸消息 } 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、通過Handler投遞消息 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覆寫handlerMessage來處理各種消息 switch (msg.what) { // 代碼省略 case DO_TRAVERSAL: if (mProfile) { Debug.startMethodTracing("ViewRoot"); } performTraversals(); if (mProfile) { Debug.stopMethodTracing(); mProfile = false; } break; case DISPATCH_POINTER: { // 4、處理DISPATCH_POINTER類型的消息,即觸摸屏幕的消息 MotionEvent event = (MotionEvent) msg.obj; try { deliverPointerEvent(event); // 5、處理觸摸消息 } finally { event.recycle(); if (msg.arg1 != 0) { finishInputEvent(); } if (LOCAL_LOGV || WATCH_POINTER) Log.i(TAG, "Done dispatching!"); } } break; // 代碼省略 } // 6、真正的處理事件 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); // 如果是ACTION_DOWN事件則進(jìn)入觸摸模式,否則為按鍵模式。 } if(Config.LOGV) { captureMotionLog("captureDispatchPointer", event); } if (mCurScrollY != 0) { event.offsetLocation(0, mCurScrollY); // 物理坐標(biāo)向邏輯坐標(biāo)的轉(zhuǎn)換 } if (MEASURE_LATENCY) { lt.sample("A Dispatching TouchEvents", System.nanoTime() - event.getEventTimeNano()); } // 7、分發(fā)事件,如果是窗口類型,則這里的mView對(duì)應(yīng)的就是PhonwWindow中的DecorView,否則為根視圖的ViewGroup。 handled = mView.dispatchTouchEvent(event); // 代碼省略 } } // 代碼省略 }
經(jīng)過層層迷霧,不管代碼7處的mView是DecorView還是非窗口界面的根視圖,其本質(zhì)都是ViewGroup,即觸摸事件最終被根視圖ViewGroup進(jìn)行分發(fā)?。?!
我們就以Activity為例來分析這個(gè)過程,我們知道顯示出來的Activity有一個(gè)頂層窗口,這個(gè)窗口的實(shí)現(xiàn)類是PhoneWindow, PhoneWindow中的內(nèi)容區(qū)域是一個(gè)DecorView類型的View,這個(gè)View這就是我們?cè)谑謾C(jī)上看到的內(nèi)容,這個(gè)DecorView是FrameLayout的子類,Activity的的dispatchTouchEvent實(shí)際上就是調(diào)用PhoneWindow的dispatchTouchEvent,我們看看源代碼吧,進(jìn)入Activity的dispatchTouchEvent函數(shù) :
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { // 1、調(diào)用的是PhoneWindow的superDispatchTouchEvent(ev) return true; } return onTouchEvent(ev); } public void onUserInteraction() { }
可以看到,如果事件為按下事件,則會(huì)進(jìn)入到onUserInteraction()這個(gè)函數(shù),該函數(shù)為空實(shí)現(xiàn),我們暫且不管它。繼續(xù)看,發(fā)現(xiàn)touch事件的分發(fā)調(diào)用了getWindow().superDispatchTouchEvent(ev)函數(shù),getWindow()獲取到的實(shí)例的類型為PhoneWindow類型,你可以在你的Activity類中使用如下方式查看getWindow()獲取到的類型:
Log.d("", "### Activiti中g(shù)etWindow()獲取的類型是 : " + this.getWindow()) ;
輸出:
08-31 03:40:17.036: D/(1688): ### Activiti中g(shù)etWindow()獲取的類型是 : com.android.internal.policy.impl.PhoneWindow@5287fe38
OK,廢話不多說,我們還是繼續(xù)看PhoneWindow中的superDispatchTouchEvent函數(shù)吧。
@Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }
恩,調(diào)用的是mDecor的superDispatchTouchEvent(event)函數(shù),這個(gè)mDecor就是我們上面所說的DecorView類型,也就是我們看到的Activity上的所有內(nèi)容的一個(gè)頂層ViewGroup,即整個(gè)ViewTree的根節(jié)點(diǎn)??纯此穆暶靼伞?/p>
// This is the top-level view of the window, containing the window decor. private DecorView mDecor;
DecorView
那么我繼續(xù)看看DecorView到底是個(gè)什么玩意兒吧。
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(); // 代碼省略 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); } // 代碼省略 }
可以看到,DecorView繼承自FrameLayout, 它對(duì)于touch事件的分發(fā)( dispatchTouchEvent )、處理都是交給super類來處理,也就是FrameLayout來處理,我們?cè)贔rameLayout中沒有看到相應(yīng)的實(shí)現(xiàn),那繼續(xù)跟蹤到FrameLayout的父類,即ViewGroup,我們看到了dispatchTouchEvent的實(shí)現(xiàn),那我們就先看ViewGroup (Android 2.3 源碼)是如何進(jìn)行事件分發(fā)的吧。
ViewGroup的Touch事件分發(fā)
/** * {@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; 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)) // 1、是否禁用攔截、是否攔截事件 // 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、迭代所有子view,查找觸摸事件在哪個(gè)子view的坐標(biāo)范圍內(nèi) final View child = children[i]; if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { child.getHitRect(frame); // 3、獲取child的坐標(biāo)范圍 if (frame.contains(scrolledXInt, scrolledYInt)) // 4、判斷發(fā)生該事件坐標(biāo)是否在該child坐標(biāo)范圍內(nèi) // 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)) // 5、child處理該事件 // 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. } } } } } 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; 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 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; } return target.dispatchTouchEvent(ev); }
這個(gè)函數(shù)代碼比較長(zhǎng),我們只看上文中標(biāo)注的幾個(gè)關(guān)鍵點(diǎn)。首先在代碼1處可以看到一個(gè)條件判斷,如果disallowIntercept和!onInterceptTouchEvent(ev)兩者有一個(gè)為true,就會(huì)進(jìn)入到這個(gè)條件判斷中。disallowIntercept是指是否禁用掉事件攔截的功能,默認(rèn)是false,也可以通過調(diào)用requestDisallowInterceptTouchEvent方法對(duì)這個(gè)值進(jìn)行修改。那么當(dāng)?shù)谝粋€(gè)值為false的時(shí)候就會(huì)完全依賴第二個(gè)值來決定是否可以進(jìn)入到條件判斷的內(nèi)部,第二個(gè)值是什么呢?onInterceptTouchEvent就是ViewGroup對(duì)事件進(jìn)行攔截的一個(gè)函數(shù),返回該函數(shù)返回false則表示不攔截事件,反之則表示攔截。第二個(gè)條件是是對(duì)onInterceptTouchEvent方法的返回值取反,也就是說如果我們?cè)趏nInterceptTouchEvent方法中返回false,就會(huì)讓第二個(gè)值為true,從而進(jìn)入到條件判斷的內(nèi)部,如果我們?cè)趏nInterceptTouchEvent方法中返回true,就會(huì)讓第二個(gè)值的整體變?yōu)閒alse,從而跳出了這個(gè)條件判斷。例如我們需要實(shí)現(xiàn)ListView滑動(dòng)刪除某一項(xiàng)的功能,那么可以通過在onInterceptTouchEvent返回true,并且在onTouchEvent中實(shí)現(xiàn)相關(guān)的判斷邏輯,從而實(shí)現(xiàn)該功能。
進(jìn)入代碼1內(nèi)部的if后,有一個(gè)for循環(huán),遍歷了當(dāng)前ViewGroup下的所有子child view,如果觸摸該事件的坐標(biāo)在某個(gè)child view的坐標(biāo)范圍內(nèi),那么該child view來處理這個(gè)觸摸事件,即調(diào)用該child view的dispatchTouchEvent。如果該child view是ViewGroup類型,那么繼續(xù)執(zhí)行上面的判斷,并且遍歷子view;如果該child view不是ViewGroup類型,那么直接調(diào)用的是View中的dispatchTouchEvent方法,除非這個(gè)child view的類型覆寫了該方法。我們看看View中的dispatchTouchEvent函數(shù):
View的Touch事件分發(fā)
/** * 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); }
該函數(shù)中,首先判斷該事件是否符合安全策略,然后判斷該view是否是enable的 ,以及是否設(shè)置了Touch Listener,mOnTouchListener即我們通過setOnTouchListener設(shè)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; }
如果mOnTouchListener.onTouch(this, event)返回false則繼續(xù)執(zhí)行onTouchEvent(event);如果mOnTouchListener.onTouch(this, event)返回true,則表示該事件被消費(fèi)了,不再傳遞,因此也不會(huì)執(zhí)行onTouchEvent(event)。這也驗(yàn)證了我們上文中留下的場(chǎng)景2,當(dāng)onTouch函數(shù)返回true時(shí),點(diǎn)擊按鈕,但我們的點(diǎn)擊事件沒有執(zhí)行。那么我們還是先來看看onTouchEvent(event)函數(shù)到底做了什么吧。
/** * 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、判斷該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(); // 獲取焦點(diǎn) } 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、點(diǎn)擊事件處理 } } } 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; }
我們看到,在onTouchEvent函數(shù)中就是對(duì)ACTION_UP、ACTION_DOWN、ACTION_MOVE等幾個(gè)事件進(jìn)行處理,而最重要的就是UP事件了,因?yàn)檫@個(gè)里面包含了對(duì)用戶點(diǎn)擊事件的處理,或者是說對(duì)于用戶而言相對(duì)重要一點(diǎn),因此放在了第一個(gè)case中。在ACTION_UP事件中會(huì)判斷該view是否enable、是否clickable、是否獲取到了焦點(diǎn),然后我們看到會(huì)通過post方法將一個(gè)PerformClick對(duì)象投遞給UI線程,如果投遞失敗則直接調(diào)用performClick函數(shù)執(zhí)行點(diǎn)擊事件。
/** * 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); }
我們看看PerformClick類吧。
private final class PerformClick implements Runnable { public void run() { performClick(); } }
可以看到,其內(nèi)部就是包裝了View類中的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; }
代碼很簡(jiǎn)單,主要就是調(diào)用了mOnClickListener.onClick(this);方法,即執(zhí)行用戶通過setOnClickListener設(shè)置進(jìn)來的點(diǎn)擊事件處理Listener。
總結(jié)
用戶觸摸屏幕產(chǎn)生一個(gè)觸摸消息,系統(tǒng)底層將該消息轉(zhuǎn)發(fā)給ViewRoot ( ViewRootImpl ),ViewRoot產(chǎn)生一個(gè)DISPATCHE_POINTER的消息,并且在handleMessage中處理該消息,最終會(huì)通過deliverPointerEvent(MotionEvent event)來處理該消息。在該函數(shù)中會(huì)調(diào)用mView.dispatchTouchEvent(event)來分發(fā)消息,該mView是一個(gè)ViewGroup類型,因此是ViewGroup的dispatchTouchEvent(event),在該函數(shù)中會(huì)遍歷所有的child view,找到該事件的觸發(fā)的左邊與每個(gè)child view的坐標(biāo)進(jìn)行對(duì)比,如果觸摸的坐標(biāo)在該child view的范圍內(nèi),則由該child view進(jìn)行處理。如果該child view是ViewGroup類型,則繼續(xù)上一步的查找過程;否則執(zhí)行View中的dispatchTouchEvent(event)函數(shù)。在View的dispatchTouchEvent(event)中首先判斷該控件是否enale以及mOnTouchListent是否為空,如果mOnTouchListener不為空則執(zhí)行mOnTouchListener.onTouch(event)方法,如果該方法返回false則再執(zhí)行View中的onTouchEvent(event)方法,并且在該方法中執(zhí)行mOnClickListener.onClick(this, event) ;方法; 如果mOnTouchListener.onTouch(event)返回true則不會(huì)執(zhí)行onTouchEvent方法,因此點(diǎn)擊事件也不會(huì)被執(zhí)行。
粗略的流程圖如下 :
相信本文所述對(duì)大家進(jìn)一步深入掌握Android程序設(shè)計(jì)有一定的借鑒價(jià)值。
相關(guān)文章
Android查看電池電量的方法(基于BroadcastReceiver)
這篇文章主要介紹了Android查看電池電量的方法,結(jié)合實(shí)例分析了Android使用BroadcastReceiver實(shí)現(xiàn)針對(duì)電池電量的查詢技巧,需要的朋友可以參考下2016-01-01優(yōu)化SimpleAdapter適配器加載效率的方法
下面小編就為大家?guī)硪黄獌?yōu)化SimpleAdapter適配器加載效率的方法。小編覺得挺不錯(cuò)的,現(xiàn)在就分享給大家,也給大家做個(gè)參考。一起跟隨小編過來看看吧2017-04-04Android 通過Messager與Service實(shí)現(xiàn)進(jìn)程間雙向通信案例詳解
這篇文章主要介紹了Android 通過Messager與Service實(shí)現(xiàn)進(jìn)程間雙向通信案例詳解,本篇文章通過簡(jiǎn)要的案例,講解了該項(xiàng)技術(shù)的了解與使用,以下就是詳細(xì)內(nèi)容,需要的朋友可以參考下2021-09-09Android項(xiàng)目實(shí)戰(zhàn)之仿網(wǎng)易頂部導(dǎo)航欄效果
這篇文章主要為大家詳細(xì)介紹了Android項(xiàng)目實(shí)戰(zhàn)之仿網(wǎng)易頂部導(dǎo)航欄效果,文中示例代碼介紹的非常詳細(xì),具有一定的參考價(jià)值,感興趣的小伙伴們可以參考一下2016-05-05關(guān)于Android WebView的loadData方法的注意事項(xiàng)分析
本篇文章是對(duì)Android中WebView的loadData方法的注意事項(xiàng)進(jìn)行了詳細(xì)的分析介紹,需要的朋友參考下2013-06-06Flutter實(shí)現(xiàn)心動(dòng)的動(dòng)畫特效
為了追求更好的用戶體驗(yàn),有時(shí)候我們需要一個(gè)類似心跳一樣跳動(dòng)著的控件來吸引用戶的注意力。本文將利用Flutter實(shí)現(xiàn)這一動(dòng)畫特效,需要的可以參考一下2022-04-04Android中制作自定義dialog對(duì)話框的實(shí)例分享
這篇文章主要介紹了Android中制作自定義dialog對(duì)話框的實(shí)例分享,安卓自帶的Dialog顯然不夠用,因而我們要繼承Dialog類來制作自己的對(duì)話框,需要的朋友可以參考下2016-04-04Android Jetpack架構(gòu)中ViewModel接口暴露的不合理探究
這篇文章主要介紹了Android Jetpack架構(gòu)組件 ViewModel詳解,ViewModel類讓數(shù)據(jù)可在發(fā)生屏幕旋轉(zhuǎn)等配置更改后繼續(xù)存在,ViewModel類旨在以注重生命周期的方式存儲(chǔ)和管理界面相關(guān)的數(shù)據(jù)。感興趣可以來學(xué)習(xí)一下2022-07-07配置一個(gè)好用的Android模擬器讓你不再對(duì)模擬器那么失望
默認(rèn)情況下的Android模擬器窗口占據(jù)了屏幕巨大的空間,而且毫無緣由的放著一個(gè)屏幕鍵盤,如果你沒親自用過模擬器的話,還有一個(gè)不易發(fā)現(xiàn)的問題:幾乎是慢到不能用2013-01-01