Android教程網
  1. 首頁
  2. Android 技術
  3. Android 手機
  4. Android 系統教程
  5. Android 游戲
 Android教程網 >> Android技術 >> 關於Android編程 >> Android的觸摸分發機制和如何實現攔截

Android的觸摸分發機制和如何實現攔截

編輯:關於Android編程

前言

在自定義ViewGroup中,有時候需要實現觸摸事件攔截,比如ListView下拉刷新就是典型的觸摸事件攔截的例子。觸摸事件攔截就是在觸摸事件被parent view攔截,而不會分發給其child,即使觸摸發生在該child身上。被攔截的事件會轉到parent view的onTouchEvent方法中進行處理。但是這個交互過程還是挺復雜的,有多種情況,今天我們就來分析一下吧。這篇分析文章已經放了一段時間了,如果有任何問題請高人指出。

觸摸事件的分發

簡單來說觸摸事件的分發會經過這麼幾個順序,dispatchTouchEvent –> onInterceptTouchEvent –> onTouchEvent,

\

假設一個Activity展示的界面有A->B->C->D四層,當事件發生之後,首先經過A的onInterceptTouchEvent(), 如果A的onInterceptTouchEvent()返回false,則會傳遞到B的onInterceptTouchEvent(),如果返回false則一次向下(內層)傳遞。如果某一層的onInterceptTouchEvent()返回true,然後就會調用該層的disatchTouchEvent()分發事件,事件不再向下傳遞。如果各層都沒有攔截事件則從最內層開始調用dispatchTouchEvent(),如果某一各層的dispatchTouchEvent()返回true,則表明該層消費了該事件,則上面層的dispatchTouEvent()不會被調用。舉一個例子:

vc/CtcS5/bPMoaO008rTzbzK973HtsjJz8C0y7WjrL7Nyse0pcP+ysK8/rvhtNO4uMrTzbywpLj2tKu13bW919PK0828oaOxyMjn0ru49kxpbmVhckxheW91dNbQ09bSu7j2VGV4dFZpZXejrLWxtKXD/tXiuPZUZXh0Vmlld8qxtKXD/srCvP674c/ItPK1vUxpbmVhckxheW91dKOsyLu689TZtb2071RleHRWaWV3oaPI57n7TGluZWFyTGF5b3V0vau0pcP+ysK8/sC5vdjBy6OsxMfDtFRleHRWaWV3vs274crVtb3Su7j2Q0FOQ0VMysK8/qOsxuTL+7Slw/6+zcrVsru1vcHLoaO1q8rHtKXD/srCvP61xLSmwO25/bPMysfSu7j2w7DF3crCvP6jrLu5ysfS1MnPw+a1xFRleHRWaWV3zqrA/aOs1f2zo8fpv/bPwqOsysK8/rTTyc+1vc/Ct9a3orW9VGV4dFZpZXfJz6OsVGV4dFZpZXfU8rvhttS4w8rCvP69+NDQtKbA7aOsyOe5+1RleHRWaWV3tKbA7cHLuMPKwrz+o6y8tFRleHRWaWV3tcRkaXNwYXRjaFRvdWNoRXZlbnS3tbvYwct0cnVlLCDEx8O0uMPKwrz+vs2xu8/7t9HBy6GjtavKx8jnuftUZXh0Vmlld7XEZGlzcGF0Y2hUb3VjaEV2ZW50t7W72LXEysdmYWxzZSwg1PK0+rHt1eK49srCvP7Du9PQsbu0psDto6y0y8qxuMPKwrz+vs274bTTz8K1vcnPo6i8tLTTY2hpbGQgtb0gdmlldyBncm91cLXEuf2zzKOp1dJwYXJlbnQgdmlld7340NC0psDtoaPI57n7cGFyZW50IHZpZXfSssO709C0psDto6zEx8O01+7W1bvhvbu4+EFjdGl2aXR5IKOoyOe5+8rHQWN0aXZpdHm0sL/ao6kgtcRvblRvdWNoRXZlbnTAtLSmwO2ho8/Cw+a+zcrHVmlld0dyb3VwtcTKwrz+t9a3orn9s8yjrLj8z+rPuLXE18rBz8frss6/vEFuZHJvaWQgVG91Y2jKwrz+t9a3orn9s8yhozxiciAvPg0KtKXD/srCvP61xMC5vdg8L3A+DQo8cD5WaWV3R3JvdXC21NPaysK8/rXEwLm92MrH0ru49ri01NO1xMH3s8yjrMjnufvE48/rttS0pcP+ysK8/r340NDAub3Yo6zEx8O0xOPQ6NKquLLQtG9uSW50ZXJjZXB0VG91Y2hFdmVudLe9t6ijrLKix9K3tbvYdHJ1ZaGjyLu687rz0Pi1xMrCvP6+zbvhsbvXqtLGtb24w1ZpZXdHcm91cLXEb25Ub3VjaEV2ZW50t723qL340NC0psDto6y2+NTauvPQ+LXEysK8/rSmwO25/bPM1tBvbkludGVyY2VwdFRvdWNoRXZlbnTW0NKysru74crVtb2689D4ysK8/qOs0vK0y8Tj0rLQ6NKquLLQtG9uVG91Y2hFdmVudLe9t6iho87Sw8fK18/Iv7S/tG9uSW50ZXJjZXB0VG91Y2hFdmVudLe9t6i1xLnZt73LtcP3IDo8L3A+DQo8cHJlIGNsYXNzPQ=="brush:java;"> Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point. Using this function takes some care, as it has a fairly complicated interaction with View.onTouchEvent(MotionEvent), and using it requires implementing that method as well as this one in the correct way. Events will be received in the following order: You will receive the down event here. The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal. For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent(). If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.

翻譯如下 :
實現這個方法來攔截所有觸摸事件。這會使得您可以監控到所有分發到你的子視圖的事件,然後您可以隨時控制當前的手勢。
使用這個方法您需要花些精力,因為它與View.onTouchEvent(MotionEvent)的交互非常復雜,並且要想使用這個功能還需要把當前ViewGroup的onTouchEvent方法和子控件的onTouchEvent方法正確地結合在一起使用。事件獲取順序如下:

你將從這裡開始接收ACTION_DOWN觸摸事件。
ACTION_DOWN觸摸事件可以由該ViewGroup自己處理,也可以由它的子控件的onTouchEvent進行處理;這就意味著你需要實現onTouchEvent(MotionEvent)方法並且返回true,這樣你才可以接收到後續的事件(以免會繼續尋找父控件進行處理)。如果你在onTouchEvent(MotionEvent)返回了true,那麼在onInterceptTouchEvent()方法中您將不會再收到後續的事件,所有這些後續的事件(例如您在ACTION_DOWN中返回了true,那麼ACTION_MOVE, ACTION_UP這些成為後續事件)將會被本類的onTouchEvent(MotionEvent)方法中被處理。


只要您在onInterceptTouchEvent方法中返回false,每個後續的事件(從當前事件到最後ACTION_UP事件)將會先分發到onInterceptTouchEvent中,然後再交給目標子控件的onTouchEvent處理 (前提是子控件的onTouchEvent返回是true )。

如果在onInterceptTouchEvent返回true,onInterceptTouchEvent方法中將不會收到後續的任何事件,目標子控件中除了ACTION_CANCEL外也不會接收所有這些後續事件,所有的後續事件將會被交付到你自己的onTouchEvent()方法中。


觸摸事件攔截示例

TouchLayout類 ( ViewGroup )

import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.FrameLayout;
import android.widget.Scroller;

public class TouchLayout extends FrameLayout {

    private String TAG = TouchLayout.class.getSimpleName();

    public TouchLayout(Context context) {
        super(context);

    }

    public TouchLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TouchLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
//        setClickable(true);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean result = super.dispatchTouchEvent(ev) ;

        return result;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // 
        final int action = MotionEventCompat.getActionMasked(ev);
        // Always handle the case of the touch gesture being complete.
        if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
            // Do not intercept touch event, let the child handle it
            return false;
        }

        TouchUtils.showEventInfo(TAG + "#   onInterceptTouchEvent", action);


        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        TouchUtils.showEventInfo(TAG + "# *** onTouchEvent", ev.getAction());
        Log.d(TAG, "### is Clickable = " + isClickable());
         return super.onTouchEvent(ev);
//        return true;
    }

}

TouchTv ( View 類型)

public class TouchTv extends TextView {

    private String TAG = TouchTv.class.getSimpleName();

    public TouchTv(Context context) {
        this(context, null);
    }

    public TouchTv(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TouchTv(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
//        setClickable(true);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        TouchUtils.showEventInfo(TAG + "#dispatchTouchEvent", ev.getAction());
        boolean result = super.dispatchTouchEvent(ev);
        Log.d(TAG, "### dispatchTouchEvent result = " + result);
        return result;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        TouchUtils.showEventInfo(TAG + "#onTouchEvent", ev.getAction());
        boolean result = super.onTouchEvent(ev);
        Log.d(TAG, "### onTouchEvent result = " + result);
        return result;
    }
}

Activity :

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.touch_event_intercept);

        View myView = findViewById(R.id.my_button);

        ValueAnimator colorAnim = ObjectAnimator.ofInt(myView,
                "backgroundColor", /* Red */
                0xFFFF8080, /* Blue */0xFF8080FF);
        colorAnim.setDuration(3000);
        colorAnim.setEvaluator(new ArgbEvaluator());
        colorAnim.setRepeatCount(ValueAnimator.INFINITE);
        colorAnim.setRepeatMode(ValueAnimator.REVERSE);
        colorAnim.start();

        ObjectAnimator objectAnimator = ObjectAnimator.ofFloat(myView, "scaleX",
                0.5f);
        objectAnimator.setDuration(3000);
        objectAnimator.setRepeatMode(ObjectAnimator.REVERSE);
        objectAnimator.start();

        Log.d("", "### Activiti中getWindow()獲取的類型是 : " + this.getWindow());

        // state list
        StateListDrawable stateListDrawable = new StateListDrawable();
        stateListDrawable.addState(new int[] {
                android.R.attr.state_enabled
        }, getResources().getDrawable(R.drawable.ic_launcher));
        stateListDrawable.addState(new int[] {
                android.R.attr.state_pressed
        }, getResources().getDrawable(R.drawable.ic_launcher));

    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        // Log.d("", "### activity dispatchTouchEvent");
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        TouchUtils.showEventInfo("activity onTouchEvent", event.getAction());
        return super.onTouchEvent(event);
    }

}

touch_event_intercept.xml :



    

情景分析

以下的情景的觸摸事件都是在TouchTv的范圍內。

情景1

條件 : 在TouchLayout的onInterceptTouchEvent中返回true進行事件攔截, 在TouchLayout的onTouchEvent中返回 true消費事件;
說明 : 觸摸事件被攔截,後續的事件不會進入到onInterceptTouchEvent ( If you return true from here, you will not receive any following events ),而直接進入TouchLayout的onTouchEvent方法進行處理。onTouchEvent返回true,表明事件被消費了,不會再冒泡給上面的Parent進行處理;
輸出 :
// 事件攔截
10-01 20:22:52.892: D/TouchLayout#   onInterceptTouchEvent(407): ### action -->  ACTION_DOWN
// 處理
10-01 20:22:52.892: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_DOWN
// DOWN的後續事件不經過onInterceptTouchEvent,直接交給TouchLayout的onTouchEvent處理
10-01 20:22:52.917: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:52.937: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:52.957: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:52.977: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:52.977: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:52.997: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:53.017: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_MOVE
10-01 20:22:53.017: D/TouchLayout# *** onTouchEvent(407): ### action -->  ACTION_UP

情景2

條件 : 在TouchLayout的onInterceptTouchEvent中在ACTION_MOVE事件時返回true進行事件攔截, TouchTv的onTouchEvent中返回false,在TouchLayout的onTouchEvent中返回 true消費事件;
說明 : 事件被攔截之前,會被分發給TouchTv的onTouchEvent進行處理;觸摸事件被攔截之後,後續的事件不會進入到onInterceptTouchEvent,也不會交給TouchTv的onTouchEvent進行處理,而是直接進入TouchLayout的onTouchEvent方法進行處理。onTouchEvent返回true,表明事件被消費了,不會再冒泡給上面的Parent進行處理;
輸出 :
// DOWN中沒有對事件進行攔截,因此可以被TouchTv進行處理
10-01 20:32:05.017: D/TouchLayout#   onInterceptTouchEvent(573): ### action -->  ACTION_DOWN
// TouchTv事件分發
10-01 20:32:05.017: D/TouchTv#dispatchTouchEvent(573): ### action -->  ACTION_DOWN
// TouchTv對事件進行處理,TouchTv的onTouchEvent返回false,導致事件交給TouchLayout的onTouchEvent處理
10-01 20:32:05.017: D/TouchTv#onTouchEvent(573): ### action -->  ACTION_DOWN
// TouchLayout的onTouchEvent處理DOWN事件
10-01 20:32:05.017: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_DOWN
// TouchLayout的onTouchEvent處理後續事件
10-01 20:32:05.062: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.082: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.267: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.287: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.307: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.307: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.312: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_UP

情景3

條件 : 在TouchLayout的onInterceptTouchEvent中返回true進行事件攔截, 但在TouchLayout的onTouchEvent中返回FALSE, 導致事件沒有被消費;
說明 : 觸摸事件被攔截,後續的事件不會進入到onInterceptTouchEvent,而直接進入TouchLayout的onTouchEvent方法進行處理。onTouchEvent返回false,表明事件沒有被消費,需要交給parent處理,如果最終該事件沒有被處理,那麼事件交給Activity的onTouchEvent處理。
輸出 :
// 事件攔截onInterceptTouchEvent
10-01 20:16:03.617: D/TouchLayout#   onInterceptTouchEvent(32675): ### action -->  ACTION_DOWN
// 事件處理onTouchEvent
10-01 20:16:03.617: D/TouchLayout# *** onTouchEvent(32675): ### action -->  ACTION_DOWN
// TouchLayout的dispatchTouchEvent最終返回了false,
10-01 20:16:03.617: D/TouchLayout(32675): ### dispatchTouchEvent, return false
// 事件沒有被處理,最終交給了Activity的onTouchEvent處理
10-01 20:16:03.617: D/activity onTouchEvent(32675): ### action -->  ACTION_DOWN
10-01 20:16:03.697: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.712: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.732: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.882: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.897: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.917: D/activity onTouchEvent(32675): ### action -->  ACTION_UP

情景4

條件 : 在TouchLayout的onInterceptTouchEvent中返回FALSE,不對觸摸進行事件攔截, TouchLayout的onTouchEvent中返回true,但在TouchTv的onTouchEvent中返回FALSE, 導致事件沒有被消費;
說明 : 觸摸事件不進行攔截,因此事件最終進入到TouchTv的onTouchEvent,但其返回false,表明事件沒有被消費,需要交給parent處理,如果最終該事件沒有被處理,那麼事件交給Activity的onTouchEvent處理。
輸出 :
“`
// TouchLayout不對事件進行攔截
10-01 20:43:04.682: D/TouchLayout# onInterceptTouchEvent(814): ### action –> ACTION_DOWN
// 事件被TouchTv分發
10-01 20:43:04.682: D/TouchTv#dispatchTouchEvent(814): ### action –> ACTION_DOWN
// 事件被TouchTv處理
10-01 20:43:04.682: D/TouchTv#onTouchEvent(814): ### action –> ACTION_DOWN
// 事件被TouchTv的處理結果為false,因此該事件需要找parent來處理
10-01 20:43:04.682: D/TouchTv(814): ### dispatchTouchEvent result = false
// 事件被交給TouchTv的parent的onTouchEvent處理,即TouchLayout的onTouchEvent,該方法返回true
// 因此後續事件繼續交給TouchLayout處理
10-01 20:43:04.682: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_DOWN
10-01 20:43:04.727: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_MOVE
10-01 20:43:04.747: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_MOVE
10-01 20:43:04.872: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_MOVE
10-01 20:43:04.892: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_MOVE
10-01 20:43:04.892: D/TouchLayout# * onTouchEvent(814): ### action –> ACTION_UP

* 情景5

 * 條件 : 在TouchLayout的onInterceptTouchEvent中返回FALSE,不對觸摸進行事件攔截, 但在TouchTv的onTouchEvent中返回true, 導致事件被消費;
說明 : 觸摸事件不進行攔截,因此事件最終進入到TouchTv的onTouchEvent,但其返回true,表明事件沒有被消費,那麼後續事件將會先到TouchLayout的onInterceptTouchEvent,然後再分發給TouchTv。原文描述為 : For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
輸出 : 
 ```
// TouchLayout不攔截事件,因此事件分發給TouchTv進行處理,而TouchTv的處理結果為true,因此後續的事件將會先從
// TouchLayout的onInterceptTouchEvent再到TouchTv的onTouchEvent
10-01 20:48:49.612: D/TouchLayout#   onInterceptTouchEvent(1030): ### action -->  ACTION_DOWN
// TouchTv處理事件
10-01 20:48:49.612: D/TouchTv#dispatchTouchEvent(1030): ### action -->  ACTION_DOWN
10-01 20:48:49.612: D/TouchTv#onTouchEvent(1030): ### action -->  ACTION_DOWN
10-01 20:48:49.612: D/TouchTv(1030): ### dispatchTouchEvent result = true
// 後續事件從TouchLayout的onInterceptTouchEvent再到TouchTv的onTouchEvent
10-01 20:48:49.697: D/TouchLayout#   onInterceptTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.697: D/TouchTv#dispatchTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.697: D/TouchTv#onTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.697: D/TouchTv(1030): ### dispatchTouchEvent result = true
10-01 20:48:49.717: D/TouchLayout#   onInterceptTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.717: D/TouchTv#dispatchTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.717: D/TouchTv#onTouchEvent(1030): ### action -->  ACTION_MOVE
10-01 20:48:49.717: D/TouchTv(1030): ### dispatchTouchEvent result = true
// UP事件直接在TouchTv中進行分發
10-01 20:48:49.782: D/TouchTv#dispatchTouchEvent(1030): ### action -->  ACTION_UP
10-01 20:48:49.782: D/TouchTv#onTouchEvent(1030): ### action -->  ACTION_UP
10-01 20:48:49.782: D/TouchTv(1030): ### dispatchTouchEvent result = true
 ```
* 情景6

 *  條件 : 在TouchLayout的onInterceptTouchEvent中的DOWN事件中返回FALSE,但在MOVE事件中返回true, 且TouchTv的onTouchEvent返回true。
說明 : 觸摸事件對DOWN事件不進行攔截,因此TouchTv可以正常的處理。但是在MOVE時對事件進行了攔截,那麼TouchTv就無法接收到MOVE以及後面的事件了,它會收到一個CANCEL事件,後續的事件將會被TouchLayout的onTouchEvent進行處理。( If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here. )
輸出 :
 ```
// TouchLayout不對DOWN進行攔截
10-01 20:56:37.642: D/TouchLayout#   onInterceptTouchEvent(1205): ### action -->  ACTION_DOWN
// TouchTv分發與處理DOWN事件
10-01 20:56:37.642: D/TouchTv#dispatchTouchEvent(1205): ### action -->  ACTION_DOWN
10-01 20:56:37.642: D/TouchTv#onTouchEvent(1205): ### action -->  ACTION_DOWN
10-01 20:56:37.642: D/TouchTv(1205): ### dispatchTouchEvent result = true
// TouchLayout對MOVE事件進行攔截
10-01 20:56:37.712: D/TouchLayout#   onInterceptTouchEvent(1205): ### action -->  ACTION_MOVE
// TouchTv收到一個CANCEL事件,然後不會不到MOVE以及後續的事件
10-01 20:56:37.712: D/TouchTv#dispatchTouchEvent(1205): ### action -->  ACTION_CANCEL
10-01 20:56:37.712: D/TouchTv#onTouchEvent(1205): ### action -->  ACTION_CANCEL
10-01 20:56:37.712: D/TouchTv(1205): ### dispatchTouchEvent result = true
// MOVE以及後續事件被TouchLayout處理
10-01 20:56:37.727: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:37.747: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:37.762: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:37.777: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:37.797: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:37.997: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:38.012: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_MOVE
10-01 20:56:38.017: D/TouchLayout# *** onTouchEvent(1205): ### action -->  ACTION_UP

總結

以上的幾種情況就是我們經常遇到的了,總結起來有幾個重要的點 :
1、如果Parent ViewGroup的onInterceptTouchEvent返回false, 並且觸摸的目標view對於觸摸事件的處理結果返回的是true,那麼後續事件會先經過parent 的onInterceptTouchEvent, 然後再交給目標view進行處理;
2、如果Parent ViewGroup的onInterceptTouchEvent返回true,即對事件進行攔截,那麼事件將不會再經過onInterceptTouchEvent,而是直接進入到onTouchEvent進行處理;如果onTouchEvent返回true,則表示該事件被處理了;如果返回FALSE,則代表事件沒有被處理,那麼事件會被上交給它的parent來處理,如果沒有parent來處理,那麼最終會交給Activity來處理;
3、如果用戶在觸摸的某個事件才攔截,那麼目標view會收到一個CANCEL事件,然後後續的事件不會再交給目標view,而被轉交給Parent的onTouchEvent方法進行處理。比如情景6當中,在TouchLayout的DOWN時不對事件進行攔截,這時事件會被TouchTv正常處理。但是在MOVE時事件被攔截了,此時TouchTv收到了一個CANCEL事件,MOVE以及後續的事件就交給了TouchLayout進行處理。這個情景就是我們做下拉刷新時要用的場景了。 我們結合ViewGroup的事件分發過程來驗證吧。代碼如下 :

/** 
 * {@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;  
    // 是否禁用攔截,如果為true表示不能攔截事件;反之,則為可以攔截事件  
    boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;  
    // ACTION_DOWN事件,即按下事件  
    if (action == MotionEvent.ACTION_DOWN) {  
        if (mMotionTarget != null) {  
            mMotionTarget = null;  
        }  
        // If we're disallowing intercept or if we're allowing and we didn't  
        // intercept。如果不允許事件攔截或者不攔截該事件,那麼執行下面的操作  
        if (disallowIntercept || !onInterceptTouchEvent(ev))         // 1、是否禁用攔截、是否攔截事件的判斷  
            // 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子view的坐標范圍內  
                final View child = children[i];  
                // 該child是可見的  
                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE  
                        || child.getAnimation() != null) {  
                    // 3、獲取child的坐標范圍  
                    child.getHitRect(frame);                 
                    // 4、判斷發生該事件坐標是否在該child坐標范圍內  
                    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處理該事件,如果返回true,那麼mMotionTarget為該child。正常情況下,  
                        // dispatchTouchEvent(ev)的返回值即onTouchEcent的返回值。因此onTouchEcent如果返回為true,  
                        // 那麼mMotionTarget為觸摸事件所在位置的child。  
                        if (child.dispatchTouchEvent(ev))       
                            // 6、 mMotionTarget為該child
                            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;  
    }  

    // 觸摸事件的目標view, 即觸摸所在的view
    final View target = mMotionTarget;  
    // 7、如果mMotionTarget為空,那麼執行super.super.dispatchTouchEvent(ev),  
    // 即View.dispatchTouchEvent(ev),就是該View Group自己處理該touch事件,只是又走了一遍View的分發過程而已.  
    // 攔截事件或者在不攔截事件且target view的onTouchEvent返回false的情況都會執行到這一步.  
    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);  
    }  

    // 8、如果沒有禁用事件攔截,並且onInterceptTouchEvent(ev)返回為true,即進行事件攔截.  ( 似乎總走不到這一步 ??? )  
    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;  
    }  
    // 9、事件不攔截,且target view在ACTION_DOWN時返回true,那麼後續事件由target來處理事件  
    return target.dispatchTouchEvent(ev);  
}

如果不對事件進來攔截,且TouchTv對事件的處理返回true,那麼在DOWN事件時,mMotionTarget就是TouchTv,後續的事件就會通過注釋9來處理,即直接交給TouvhTv來處理。如果在DOWN時就攔截事件,那麼mMotionTarget為空,則會執行注釋7出的代碼,一直調用super.dispatchTouchEvent處理事件,即調用本類的事件處理,最終會調用onTouchEvent方法。如果在DOWN時不攔截,MOVE時攔截,那麼會引發注釋8的代碼,target view收到一個cancel事件,且mMotionTarget被置空,後續事件在注釋7出的代理進行處理,即在自己的onTouchEvent中進行處理。

  1. 上一頁:
  2. 下一頁:
熱門文章
閱讀排行版
Copyright © Android教程網 All Rights Reserved