Android ViewGroup 觸控事件傳遞機制
引言
上一篇部落格我們學習了Android View 觸控事件傳遞機制,不瞭解的同學可以檢視Android View 觸控事件傳遞機制。今天繼續學習Android觸控事件傳遞機制,這篇部落格將和大家一起探討ViewGroup的觸控事件傳遞機制。
示例
示例程式碼如下:
public class MainActivity extends ActionBarActivity {
private String TAG = "MainActivity";
private MyViewGroup parentView;
private Button childView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
parentView = (MyViewGroup) findViewById(R.id.parent);
childView = (Button) findViewById(R.id.child);
childView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "childView=====onClick");
}
});
parentView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e(TAG, "parentView=====onTouch" );
return false;
}
});
parentView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "parentView=====onClick");
}
});
}
}
自定義MyViewGroup,並且重寫dispatchTouchEvent方法新增列印日誌,重寫onInterceptTouchEvent方法新增列印日誌:
public class MyViewGroup extends LinearLayout {
private String TAG = "MyViewGroup";
public MyViewGroup(Context context) {
super(context);
}
public MyViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.e(TAG, "MyViewGroup=====dispatchTouchEvent "+ev.getAction());
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e(TAG, "MyViewGroup=====onInterceptTouchEvent");
return super.onInterceptTouchEvent(ev);
}
}
佈局如下:
<com.xjp.viewgrouptouchdemo.MyViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/parent"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<Button
android:id="@+id/child"
android:layout_width="100dp"
android:layout_height="60dp"
android:background="@drawable/image1" />
</com.xjp.viewgrouptouchdemo.MyViewGroup>
分別點選Button按鈕和空白區域,列印結果如下:
08-01 17:02:56.792 14706-14706/com.xjp.viewgrouptouchdemo E/MyViewGroup﹕ MyViewGroup=====dispatchTouchEvent
08-01 17:02:56.792 14706-14706/com.xjp.viewgrouptouchdemo E/MainActivity﹕ childView=====onClick
08-01 17:03:31.046 14706-14706/com.xjp.viewgrouptouchdemo E/MyViewGroup﹕ MyViewGroup=====dispatchTouchEvent
08-01 17:03:31.046 14706-14706/com.xjp.viewgrouptouchdemo E/MainActivity﹕ parentView=====onTouch1
08-01 17:03:31.046 14706-14706/com.xjp.viewgrouptouchdemo E/MainActivity﹕ parentView=====onClick
從上面列印可以看出,在ViewGroup巢狀Button佈局中,僅僅點選Button按鈕時只會執行Button的觸控事件,不會執行ViewGroup的觸控事件。當你點選Button以外的空白區域時,才會執行ViewGroup的觸控事件。那為什麼在ViewGroup巢狀View時只會執行View的觸控事件而不執行ViewGroup的觸控事件呢?待著這個疑問,我們來分析下ViewGroup原始碼中的dispatchTouchEvent方法。為了方便起見,我這裡都是分析的Android2.0的原始碼。
ViewGroup#dispatchTouchEvent
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
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)) {
// 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--) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
child.getHitRect(frame);
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);
if (child.dispatchTouchEvent(ev)) {
// 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);
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;
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);
return target.dispatchTouchEvent(ev);
}
分析:
1. 程式碼3-8行,獲取當前手指在螢幕上觸控點選的座標位置,用於判斷當前手指觸控點選的是View區域還是ViewGroup區域。
2. 程式碼第10行,獲得disallowIntercept的值,disallowIntercept指的是是否禁用掉事件攔截功能,預設值是false,你可以呼叫requestDisallowInterceptTouchEvent方法修改它。
3. 程式碼第12行,手指觸控手勢是先ACTION_DOWN操作,所以條件滿足,進入if條件。
4. 程式碼第13-19行,清除當前手機螢幕上觸控點選物件,也就是將mMotionTarget設定為null。意思是在點選手機螢幕之前是沒有任何觸控點選物件的。
5. 程式碼第22行,由於disallowIntercept預設值是false,所以條件是否滿足完全取決於方法onInterceptTouchEvent返回值取反。而我們進入該方法會發現裡面的實現僅僅是返回一個false。也就是if條件滿足。
6. 程式碼第31行,通過一個for迴圈遍歷當前ViewGroup下所以子View。
7. 程式碼第35行,獲取遍歷子View在螢幕上的座標位置,然後程式碼第36行,判斷當前螢幕手指觸控點選座標是否包含遍歷的子View在螢幕上的座標位置範圍?如果包含,者表示當前手指觸控點選的地方是該子View,也就是點選了Button。否則表示當前手指觸控並沒有點選到ViewGroup中的子View,也就是點選到了空白區域。
8. 程式碼第41行,呼叫子View的dispatchTouchEvent方法來處理View的觸控事件分發,這裡一步就是我們上一篇部落格分析的 Android View 觸控事件傳遞機制入口。在這篇部落格中我們知道,當View是可點選的或者長安點選或者設定了setOnClickListener點選監聽事件的,View#dispatchTouchEvent方法一律返回true,否則返回false。所以當條件滿足,也就是子View設定了點選事件時ViewGroup#dispatchTouchEvent方法返回true,觸控物件mMotionTarget = child賦值成當前點選的子Viwe執行結束。因此這也驗證了上面示例程式碼,當button設定了點選事件時只執行了Button的onClick事件,並沒有執行任何關於ViewGroup的觸控點選事件。
9. 程式碼第66-72行,假如上面的View#dispatchTouchEvent方法返回false,表示子View不可點選(可以參考上一篇部落格),此時mMotionTarget依然為null,那麼target==null條件滿足。執行父類的dispatchTouchEvnet方法,也就是View的dispatchTouchEvent方法。由於ViewGroup的父類是View,所以此處表示執行了ViewGroup的dispatchTouchEvent方法。言外之意就是,當ViewGroup巢狀的子View不可點選且沒有設定setOnClickListener點選監聽事件時,點選View先觸發子View的觸控事件,然後在觸發ViewGroup的觸控事件,執行了ViewGroup#dispatchTouchEvent方法,並且返回了,後面程式碼不執行。
10. 程式碼第76-103行,主要是執行子View的ACTION_UP和ACTION_CANCEL手勢操作的,邏輯這裡就不具體分析了,可以參考上一篇部落格。
總結:有上面分析我們知道。
- onInterceptTouchEvent方法是用於ViewGroup對子View的觸控事件攔截功能,預設返回false,不攔截子View的觸控事件,可以重寫該方法,返回true來攔截子View的觸控事件傳遞。此時只會執行ViewGroup的觸控事件傳遞。
- 當子View是不可點選的且沒有設定setOnClickListener點選監聽事件時,會先執行子View的觸控事件,然後在執行ViewGroup的觸控事件。
現在倆驗證以上兩個結論。
onInterceptTouchEvent返回true
修改MyViewGroup程式碼
public class MyViewGroup extends LinearLayout {
private String TAG = "MyViewGroup";
public MyViewGroup(Context context) {
super(context);
requestDisallowInterceptTouchEvent(false);
}
public MyViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.e(TAG, "MyViewGroup=====dispatchTouchEvent ");
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
return true;
}
點選Button按鈕,列印結果如下:
08-01 18:36:56.815 29910-29910/com.xjp.viewgrouptouchdemo E/MyViewGroup﹕ MyViewGroup=====dispatchTouchEvent
08-01 18:36:56.825 29910-29910/com.xjp.viewgrouptouchdemo E/MainActivity﹕ parentView=====onTouch1
08-01 18:36:56.825 29910-29910/com.xjp.viewgrouptouchdemo E/MainActivity﹕ parentView=====onClick
有列印可以看出,當重寫onInterceptTouchEvent方法返回true時,是不會執行Button的觸控點選事件的。也正好驗證了前面的結論:當ViewGroup重寫onInterceptTouchEvent方法返回true時,也就是攔截子View的觸控事件傳遞,此時只會執行ViewGroup的觸控事件。
子View不可點選且沒設定setOnClickListener
程式碼修改如下:
public class MainActivity extends ActionBarActivity {
private String TAG = "MainActivity";
private MyViewGroup parentView;
private ImageView childView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
parentView = (MyViewGroup) findViewById(R.id.parent);
childView = (ImageView) findViewById(R.id.child);
childView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e(TAG, "childView=====onTouch");
return false;
}
});
parentView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e(TAG, "parentView=====onTouch" +event.getAction());
return false;
}
});
parentView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "parentView=====onClick");
}
});
}
}
將Button換成ImageView,並且不設定setOnClickListener事件。點選ImageView列印日誌如下:
08-01 18:52:44.720 31219-31219/com.xjp.viewgrouptouchdemo E/MyViewGroup﹕ MyViewGroup=====dispatchTouchEvent
08-01 18:52:44.720 31219-31219/com.xjp.viewgrouptouchdemo E/MainActivity﹕ childView=====onTouch
08-01 18:52:44.730 31219-31219/com.xjp.viewgrouptouchdemo E/MainActivity﹕ parentView=====onTouch0
parentView=====onClick
有列印可以看出,即執行了子View ImageView的觸控事件,也執行了ViewGroup的觸控事件。由於ImageView預設情況是不可點選的,因此:當子View不可點選或者麼有設定setOnClickListener點選事件時,點選子View是先執行View的觸控事件,然後在執行ViewGroup的觸控事件的。這也驗證了ViewGroup#dispatchTouchEvent小節的第9點。
最後附帶上一幅ViewGroup觸控事件傳遞流程圖
總結
- 可以在ViewGroup裡重寫onInterceptTouchEvent方法來決定是否攔截子View的傳遞事件,系統預設返回false,表示不攔截子View的事件分發傳遞;如果重寫返回true,表示攔截子View的觸控事件。
- 當子View是可點選的或者設定了setOnClickListener點選事件時,android觸控事件分發是不會傳遞到ViweGroup的,也就是隻會執行View的觸控事件,不會執行ViewGroup的觸控事件。
- 當子View不可點選且沒有設定setOnClickListener點選事件時,Android觸控事件是先分發到View,View先執行dispatchTouchEvent觸控事件,然後在傳遞到ViewGroup,ViewGroup執行dispatchTouchEvent觸控事件。
- Android事件分發先傳遞到View,在由View決定是否傳遞到ViewGroup。