一直想寫事件分發機制的文章,不管咋樣,也得自己研究下事件分發的源碼,寫出心得~
首先我們先寫個簡單的例子來測試View的事件轉發的流程~
1、案例
爲了更好的研究View的事件轉發,我們自定以一個MyButton繼承Button,然後把跟事件傳播有關的方法進行復寫,然後添加上日誌~
MyButton
- package com.example.zhy_event03;
- import android.content.Context;
- import android.util.AttributeSet;
- import android.util.Log;
- import android.view.MotionEvent;
- import android.widget.Button;
- public class MyButton extends Button
- {
- private static final String TAG = MyButton.class.getSimpleName();
- public MyButton(Context context, AttributeSet attrs)
- {
- super(context, attrs);
- }
- @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 dispatchTouchEvent(MotionEvent event)
- {
- int action = event.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(event);
- }
- }
在onTouchEvent和dispatchTouchEvent中打印了日誌~
然後把我們自定義的按鈕加到主佈局文件中;
佈局文件:
- <LinearLayout 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" />
- </LinearLayout>
最後看一眼MainActivity的代碼
- package com.example.zhy_event03;
- import android.app.Activity;
- import android.os.Bundle;
- import android.util.Log;
- import android.view.MotionEvent;
- import android.view.View;
- import android.view.View.OnTouchListener;
- import android.widget.Button;
- public class MainActivity extends Activity
- {
- protected static final String TAG = "MyButton";
- private Button mButton ;
- @Override
- protected void onCreate(Bundle savedInstanceState)
- {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- mButton = (Button) findViewById(R.id.id_btn);
- mButton.setOnTouchListener(new OnTouchListener()
- {
- @Override
- public boolean onTouch(View v, MotionEvent event)
- {
- int action = event.getAction();
- switch (action)
- {
- case MotionEvent.ACTION_DOWN:
- Log.e(TAG, "onTouch ACTION_DOWN");
- break;
- case MotionEvent.ACTION_MOVE:
- Log.e(TAG, "onTouch ACTION_MOVE");
- break;
- case MotionEvent.ACTION_UP:
- Log.e(TAG, "onTouch ACTION_UP");
- break;
- default:
- break;
- }
- return false;
- }
- });
- }
- }
在MainActivity中,我們還給MyButton設置了OnTouchListener這個監聽~
好了,跟View事件相關一般就這三個地方了,一個onTouchEvent,一個dispatchTouchEvent,一個setOnTouchListener;
下面我們運行,然後點擊按鈕,查看日誌輸出:
- 08-31 06:09:39.030: E/MyButton(879): dispatchTouchEvent ACTION_DOWN
- 08-31 06:09:39.030: E/MyButton(879): onTouch ACTION_DOWN
- 08-31 06:09:39.049: E/MyButton(879): onTouchEvent ACTION_DOWN
- 08-31 06:09:39.138: E/MyButton(879): dispatchTouchEvent ACTION_MOVE
- 08-31 06:09:39.138: E/MyButton(879): onTouch ACTION_MOVE
- 08-31 06:09:39.147: E/MyButton(879): onTouchEvent ACTION_MOVE
- 08-31 06:09:39.232: E/MyButton(879): dispatchTouchEvent ACTION_UP
- 08-31 06:09:39.248: E/MyButton(879): onTouch ACTION_UP
- 08-31 06:09:39.248: E/MyButton(879): onTouchEvent ACTION_UP
我有意點擊的時候蹭了一下,不然不會觸發MOVE,手抖可能會打印一堆MOVE的日誌~~~
好了,可以看到,不管是DOWN,MOVE,UP都會按照下面的順序執行:
1、dispatchTouchEvent
2、 setOnTouchListener的onTouch
3、onTouchEvent
下面就跟隨日誌的腳步開始源碼的探索~
2、dispatchTouchEvent
首先進入View的dispatchTouchEvent
- /**
- * 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);
- }
直接看13行:首先判斷mOnTouchListener不爲null,並且view是enable的狀態,然後 mOnTouchListener.onTouch(this, event)返回true,這三個條件如果都滿足,直接return true ; 也就是下面的onTouchEvent(event)不會被執行了;
那麼mOnTouchListener是和方神聖,我們來看看:
- /**
- * 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;
- }
也就是說:如果我們設置了setOnTouchListener,並且return true,那麼View自己的onTouchEvent就不會被執行了,當然了,本例我們return false,我們還得往下探索 ;
已經解決一個常見的問題:View的onTouchListener和onTouchEvent的調用關係,相信大家應該已經明白了~let's go;繼續往下。
3、View的onTouchEvent:
接下來是View的onTouchEvent:
- /**
- * 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) {
- // 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;
- }
代碼還是比較長的,
10-15行,如果當前View是Disabled狀態且是可點擊則會消費掉事件(return true);可以忽略,不是我們的重點;17-21行,如果設置了mTouchDelegate,則會將事件交給代理者處理,直接return true,如果大家希望自己的View增加它的touch範圍,可以嘗試使用TouchDelegate,這裏也不是重點,可以忽略;
接下來到我們的重點了:
23行的判斷:如果我們的View可以點擊或者可以長按,則,注意IF的範圍,最終一定return true ;
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
//...
return true;
}
接下來就是 switch (event.getAction())了,判斷事件類型,DOWN,MOVE,UP等;
我們按照例子執行的順序,先看 case MotionEvent.ACTION_DOWN (71-78行):
1、MotionEvent.ACTION_DOWN
75行:給mPrivateFlags設置一個PREPRESSED的標識
76行:設置mHasPerformedLongPress=false;表示長按事件還未觸發;
77行:發送一個延遲爲ViewConfiguration.getTapTimeout()的延遲消息,到達延時時間後會執行CheckForTap()裏面的run方法:
1、ViewConfiguration.getTapTimeout()爲115毫秒;
2、CheckForTap
- private final class CheckForTap implements Runnable {
- public void run() {
- mPrivateFlags &= ~PREPRESSED;
- mPrivateFlags |= PRESSED;
- refreshDrawableState();
- if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
- postCheckForLongClick(ViewConfiguration.getTapTimeout());
- }
- }
- }
在run方法裏面取消mPrivateFlags的PREPRESSED,然後設置PRESSED標識,刷新背景,如果View支持長按事件,則再發一個延時消息,檢測長按;
- private void postCheckForLongClick(int delayOffset) {
- mHasPerformedLongPress = false;
- if (mPendingCheckForLongPress == null) {
- mPendingCheckForLongPress = new CheckForLongPress();
- }
- mPendingCheckForLongPress.rememberWindowAttachCount();
- postDelayed(mPendingCheckForLongPress,
- ViewConfiguration.getLongPressTimeout() - delayOffset);
- }
- class CheckForLongPress implements Runnable {
- private int mOriginalWindowAttachCount;
- public void run() {
- if (isPressed() && (mParent != null)
- && mOriginalWindowAttachCount == mWindowAttachCount) {
- if (performLongClick()) {
- mHasPerformedLongPress = true;
- }
- }
- }
可以看到,當用戶按下,首先會設置標識爲PREPRESSED
如果115後,沒有擡起,會將View的標識設置爲PRESSED且去掉PREPRESSED標識,然後發出一個檢測長按的延遲任務,延時爲:ViewConfiguration.getLongPressTimeout() - delayOffset(500ms -115ms),這個115ms剛好時檢測額PREPRESSED時間;也就是用戶從DOWN觸發開始算起,如果500ms內沒有擡起則認爲觸發了長按事件:
1、如果此時設置了長按的回調,則執行長按時的回調,且如果長按的回調返回true;才把mHasPerformedLongPress置爲ture;
2、否則,如果沒有設置長按回調或者長按回調返回的是false;則mHasPerformedLongPress依然是false;
好了DOWN就分析完成了;大家回個神,下面回到VIEW的onTouchEvent中的ACTION_MOVE:
2、MotionEvent.ACTION_MOVE
86到105行:
87-88行:拿到當前觸摸的x,y座標;
91行判斷當然觸摸點有沒有移出我們的View,如果移出了:
1、執行removeTapCallback();
2、然後判斷是否包含PRESSED標識,如果包含,移除長按的檢查:removeLongPressCallback();
3、最後把mPrivateFlags中PRESSED標識去除,刷新背景;
- private void removeTapCallback() {
- if (mPendingCheckForTap != null) {
- mPrivateFlags &= ~PREPRESSED;
- removeCallbacks(mPendingCheckForTap);
- }
- }
如果115ms後,你才移出控件外,則你的當前mPrivateFlags一定爲PRESSED且發送了長按的檢測;
就會走上面的2和3;首先移除removeLongPressCallback()
private void removeLongPressCallback() {
if (mPendingCheckForLongPress != null) {
removeCallbacks(mPendingCheckForLongPress);
}
}
然後把mPrivateFlags中PRESSED標識去除,刷新背景;
好了,MOVE我們也分析完成了,總結一下:只要用戶移出了我們的控件:則將mPrivateFlags取出PRESSED標識,且移除所有在DOWN中設置的檢測,長按等;
下面再回個神,回到View的onTouchEvent的ACTION_UP:
3、MotionEvent.ACTION_UP
26到69行:
27行:判斷mPrivateFlags是否包含PREPRESSED
28行:如果包含PRESSED或者PREPRESSED則進入執行體,也就是無論是115ms內或者之後擡起都會進入執行體。
36行:如果mHasPerformedLongPress沒有被執行,進入IF
38行:removeLongPressCallback();移除長按的檢測
45-50行:如果mPerformClick如果mPerformClick爲null,初始化一個實例,然後立即通過handler添加到消息隊列尾部,如果添加失敗則直接執行 performClick();添加成功,在mPerformClick的run方法中就是執行performClick();
終於執行了我們的click事件了,下面看一下performClick()方法:
- public boolean performClick() {
- sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
- if (mOnClickListener != null) {
- playSoundEffect(SoundEffectConstants.CLICK);
- mOnClickListener.onClick(this);
- return true;
- }
- return false;
- }
if (mOnClickListener != null) {
mOnClickListener.onClick(this);
return true;
}
久違了~我們的mOnClickListener ;
別激動,還沒結束,回到ACTION_UP,
58行:如果prepressed爲true,進入IF體:
爲mPrivateFlags設置表示爲PRESSED,刷新背景,125毫秒後執行mUnsetPressedState
否則:mUnsetPressedState.run();立即執行;也就是不管咋樣,最後mUnsetPressedState.run()都會執行;
看看這個UnsetPressedState主要幹什麼:
private final class UnsetPressedState implements Runnable {
public void run() {
setPressed(false);
}
}
public void setPressed(boolean pressed) {
if (pressed) {
mPrivateFlags |= PRESSED;
} else {
mPrivateFlags &= ~PRESSED;
}
refreshDrawableState();
dispatchSetPressed(pressed);
}
把我們的mPrivateFlags中的PRESSED取消,然後刷新背景,把setPress轉發下去。
ACTION_UP的最後一行:removeTapCallback(),如果mPendingCheckForTap不爲null,移除;
4、總結
好了,代碼跨度還是相當大的,下面需要總結下:
1、整個View的事件轉發流程是:
View.dispatchEvent->View.setOnTouchListener->View.onTouchEvent
在dispatchTouchEvent中會進行OnTouchListener的判斷,如果OnTouchListener不爲null且返回true,則表示事件被消費,onTouchEvent不會被執行;否則執行onTouchEvent。
2、onTouchEvent中的DOWN,MOVE,UP
DOWN時:
a、首先設置標誌爲PREPRESSED,設置mHasPerformedLongPress=false ;然後發出一個115ms後的mPendingCheckForTap;
b、如果115ms內沒有觸發UP,則將標誌置爲PRESSED,清除PREPRESSED標誌,同時發出一個延時爲500-115ms的,檢測長按任務消息;
c、如果500ms內(從DOWN觸發開始算),則會觸發LongClickListener:
此時如果LongClickListener不爲null,則會執行回調,同時如果LongClickListener.onClick返回true,才把mHasPerformedLongPress設置爲true;否則mHasPerformedLongPress依然爲false;
MOVE時:
主要就是檢測用戶是否劃出控件,如果劃出了:
115ms內,直接移除mPendingCheckForTap;
115ms後,則將標誌中的PRESSED去除,同時移除長按的檢查:removeLongPressCallback();
UP時:
a、如果115ms內,觸發UP,此時標誌爲PREPRESSED,則執行UnsetPressedState,setPressed(false);會把setPress轉發下去,可以在View中複寫dispatchSetPressed方法接收;
b、如果是115ms-500ms間,即長按還未發生,則首先移除長按檢測,執行onClick回調;
c、如果是500ms以後,那麼有兩種情況:
i.設置了onLongClickListener,且onLongClickListener.onClick返回true,則點擊事件OnClick事件無法觸發;
ii.沒有設置onLongClickListener或者onLongClickListener.onClick返回false,則點擊事件OnClick事件依然可以觸發;d、最後執行mUnsetPressedState.run(),將setPressed傳遞下去,然後將PRESSED標識去除;
最後問個問題,然後再運行個例子結束:
1、setOnLongClickListener和setOnClickListener是否只能執行一個
不是的,只要setOnLongClickListener中的onClick返回false,則兩個都會執行;返回true則會屏幕setOnClickListener
最後我們給MyButton同時設置setOnClickListener和setOnLongClickListener,運行看看:
- package com.example.zhy_event03;
- import android.app.Activity;
- import android.os.Bundle;
- import android.util.Log;
- import android.view.MotionEvent;
- import android.view.View;
- import android.view.View.OnClickListener;
- import android.view.View.OnLongClickListener;
- import android.view.View.OnTouchListener;
- import android.widget.Button;
- import android.widget.Toast;
- public class MainActivity extends Activity
- {
- protected static final String TAG = "MyButton";
- private Button mButton ;
- @Override
- protected void onCreate(Bundle savedInstanceState)
- {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- mButton = (Button) findViewById(R.id.id_btn);
- mButton.setOnTouchListener(new OnTouchListener()
- {
- @Override
- public boolean onTouch(View v, MotionEvent event)
- {
- int action = event.getAction();
- switch (action)
- {
- case MotionEvent.ACTION_DOWN:
- Log.e(TAG, "onTouch ACTION_DOWN");
- break;
- case MotionEvent.ACTION_MOVE:
- Log.e(TAG, "onTouch ACTION_MOVE");
- break;
- case MotionEvent.ACTION_UP:
- Log.e(TAG, "onTouch ACTION_UP");
- break;
- default:
- break;
- }
- return false;
- }
- });
- mButton.setOnClickListener(new OnClickListener()
- {
- @Override
- public void onClick(View v)
- {
- Toast.makeText(getApplicationContext(), "onclick",Toast.LENGTH_SHORT).show();
- }
- });
- mButton.setOnLongClickListener(new OnLongClickListener()
- {
- @Override
- public boolean onLongClick(View v)
- {
- Toast.makeText(getApplicationContext(), "setOnLongClickListener",Toast.LENGTH_SHORT).show();
- return false;
- }
- });
- }
- }
可以看到LongClickListener已經ClickListener都觸發了~
最後,本篇博文完成了對View的事件分發機制的整個流程的說明,並且對源碼進行了分析;