管理 ViewGroup 中的觸控事件

處理觸控事件中的 ViewGroup特別照顧 因為 ViewGroup 包含具有不同目標的子項是很常見的情況 不是 ViewGroup 本身的觸控事件。為了確保每項資料檢視正確收到 指定的觸控事件，則會覆寫 onInterceptTouchEvent() 方法。

請參閱下列相關資源：

• 輸入事件總覽
• 感應器總覽
• 將自訂檢視畫面設為互動式

攔截 ViewGroup 中的觸控事件

偵測到觸控事件時，系統就會呼叫 onInterceptTouchEvent() 方法 ViewGroup 的表面，包括其子項的表面。如果 onInterceptTouchEvent() 會傳回 true， MotionEvent ，表示該物件不會傳遞至子項，而是傳送至 onTouchEvent() 方法。

onInterceptTouchEvent() 方法可讓家長查看觸控事件 如果從 onInterceptTouchEvent() 退貨：true， 先前處理觸控事件的子項檢視畫面會收到 ACTION_CANCEL, 之後的事件會傳送到父項的 onTouchEvent() 方法 以便照常處理onInterceptTouchEvent() 也可以傳回 false 和 監控事件向下瀏覽檢視區塊階層至其平時的目標，從而處理 以及自己的 onTouchEvent() 的活動

在以下程式碼片段中，MyViewGroup 類別會擴充 ViewGroup。 MyViewGroup 包含多個子檢視畫面。在孩童檢視模式上拖曳手指 子項檢視畫面不會再擷取觸控事件，而 MyViewGroup 會處理觸控事件 就會觸發這類事件不過，如果您在孩童檢視畫面中輕觸按鈕，或捲動子項， 垂直檢視畫面，父項不會攔截這些觸控事件，因為子項是必要的 目標。在這種情況下，onInterceptTouchEvent() 會傳回 false，而 系統不會呼叫 MyViewGroup 類別的 onTouchEvent()。

Kotlin

class MyViewGroup @JvmOverloads constructor(
        context: Context,
        private val mTouchSlop: Int = ViewConfiguration.get(context).scaledTouchSlop
) : ViewGroup(context) {
    ...
    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        // This method only determines whether you want to intercept the motion.
        // If this method returns true, onTouchEvent is called and you can do
        // the actual scrolling there.
        return when (ev.actionMasked) {
            // Always handle the case of the touch gesture being complete.
            MotionEvent.ACTION_CANCEL, MotionEvent.ACTION_UP -> {
                // Release the scroll.
                mIsScrolling = false
                false // Don't intercept the touch event. Let the child handle it.
            }
            MotionEvent.ACTION_MOVE -> {
                if (mIsScrolling) {
                    // You're currently scrolling, so intercept the touch event.
                    true
                } else {

                    // If the user drags their finger horizontally more than the
                    // touch slop, start the scroll.

                    // Left as an exercise for the reader.
                    val xDiff: Int = calculateDistanceX(ev)

                    // Touch slop is calculated using ViewConfiguration constants.
                    if (xDiff > mTouchSlop) {
                        // Start scrolling!
                        mIsScrolling = true
                        true
                    } else {
                        false
                    }
                }
            }
            ...
            else -> {
                // In general, don't intercept touch events. The child view
                // handles them.
                false
            }
        }
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        // Here, you actually handle the touch event. For example, if the action
        // is ACTION_MOVE, scroll this container. This method is only called if
        // the touch event is intercepted in onInterceptTouchEvent.
        ...
    }
}

Java

public class MyViewGroup extends ViewGroup {

    private int mTouchSlop;
    ...
    ViewConfiguration vc = ViewConfiguration.get(view.getContext());
    mTouchSlop = vc.getScaledTouchSlop();
    ...
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // This method only determines whether you want to intercept the motion.
        // If this method returns true, onTouchEvent is called and you can do
        // the actual scrolling there.

        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) {
            // Release the scroll.
            mIsScrolling = false;
            return false; // Don't intercept touch event. Let the child handle it.
        }

        switch (action) {
            case MotionEvent.ACTION_MOVE: {
                if (mIsScrolling) {
                    // You're currently scrolling, so intercept the touch event.
                    return true;
                }

                // If the user drags their finger horizontally more than the
                // touch slop, start the scroll.

                // Left as an exercise for the reader.
                final int xDiff = calculateDistanceX(ev);

                // Touch slop is calculated using ViewConfiguration constants.
                if (xDiff > mTouchSlop) {
                    // Start scrolling.
                    mIsScrolling = true;
                    return true;
                }
                break;
            }
            ...
        }

        // In general, don't intercept touch events. The child view handles them.
        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        // Here, you actually handle the touch event. For example, if the
        // action is ACTION_MOVE, scroll this container. This method is only
        // called if the touch event is intercepted in onInterceptTouchEvent.
        ...
    }
}

請注意，ViewGroup 也提供 requestDisallowInterceptTouchEvent() 方法。如果子項不需要父項及其父項，ViewGroup 會呼叫這個方法 祖系，透過 onInterceptTouchEvent() 攔截觸控事件。

處理 ACTION_OUTSIDE 事件

如果 ViewGroup 收到包含 MotionEvent ACTION_OUTSIDE, 事件預設不會分派給其子項如要處理 MotionEvent ACTION_OUTSIDE，任一覆寫值 dispatchTouchEvent(MotionEvent event) 派出至適當的 View 處理 Window.Callback—用於 例如 Activity。

使用 ViewConfiguration 常數

上述程式碼片段使用目前的 ViewConfiguration 初始化變數 名為 mTouchSlop。您可以使用 ViewConfiguration 類別存取 常見的距離、速度和時間。

「觸控筆」是指使用者的輕觸手勢在手勢結束之前的距離 (以像素為單位) 會解讀為捲動通常用於防止使用者意外捲動 目前正在執行其他觸控操作，例如輕觸螢幕上的元素。

以下是另外兩種常用的 ViewConfiguration 方法： getScaledMinimumFlingVelocity() 和 getScaledMaximumFlingVelocity()。 這些方法分別傳回最小和最大速率，以啟動測量的快速滑過量 以每秒像素為單位例如：

Kotlin

private val vc: ViewConfiguration = ViewConfiguration.get(context)
private val mSlop: Int = vc.scaledTouchSlop
private val mMinFlingVelocity: Int = vc.scaledMinimumFlingVelocity
private val mMaxFlingVelocity: Int = vc.scaledMaximumFlingVelocity
...
MotionEvent.ACTION_MOVE -> {
    ...
    val deltaX: Float = motionEvent.rawX - mDownX
    if (Math.abs(deltaX) > mSlop) {
        // A swipe occurs, do something.
    }
    return false
}
...
MotionEvent.ACTION_UP -> {
    ...
    if (velocityX in mMinFlingVelocity..mMaxFlingVelocity && velocityY < velocityX) {
        // The criteria are satisfied, do something.
    }
}

Java

ViewConfiguration vc = ViewConfiguration.get(view.getContext());
private int mSlop = vc.getScaledTouchSlop();
private int mMinFlingVelocity = vc.getScaledMinimumFlingVelocity();
private int mMaxFlingVelocity = vc.getScaledMaximumFlingVelocity();
...
case MotionEvent.ACTION_MOVE: {
    ...
    float deltaX = motionEvent.getRawX() - mDownX;
    if (Math.abs(deltaX) > mSlop) {
        // A swipe occurs, do something.
    }
...
case MotionEvent.ACTION_UP: {
    ...
    } if (mMinFlingVelocity <= velocityX && velocityX <= mMaxFlingVelocity
            && velocityY < velocityX) {
        // The criteria are satisfied, do something.
    }
}

展開子項檢視畫面的可觸控區域

Android 提供 只需使用 TouchDelegate 類別即可 可讓父項將子項檢視畫面的可觸控區域延伸至子項邊界之外。這個 如果孩子必須小，但需要更大的觸控區域，那麼這項功能就非常實用。您還可以使用 縮短孩子觸控區域。

在以下範例中 ImageButton是_委派代表 view_—也就是由父項延伸的觸控區域子項。以下是版面配置檔案：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/parent_layout"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context=".MainActivity" >

     <ImageButton android:id="@+id/button"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:background="@null"
          android:src="@drawable/icon" />
</RelativeLayout>

下列程式碼片段已完成這些工作：

• 取得父母檢視模式並張貼 Runnable 發出相關的要求這可確保父項在呼叫 getHitRect() 方法。getHitRect() 方法會取得子項的命中矩形 (或 可輕觸區域)。
• 找出 ImageButton 子項檢視畫面並呼叫 getHitRect()，取得 兒童可觸控區域的邊界。
• 擴充 ImageButton 子項檢視區塊命中矩形的邊界。
• 將 TouchDelegate 例項化，並傳入已展開的點擊矩形和 ImageButton 子項檢視畫面做為參數。
• 設定父項檢視畫面的 TouchDelegate，以便在觸控委派代表內部輕觸 上下限會轉送到子項。

其容量為 ImageButton 子項檢視畫面的觸控委派，以及父項檢視畫面 接收所有觸控事件。如果觸控事件在子項的點擊矩形內發生，系統會為父項 將觸控事件傳送給子項進行處理。

Kotlin

public class MainActivity : Activity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Post in the parent's message queue to make sure the parent lays out
        // its children before you call getHitRect().
        findViewById<View>(R.id.parent_layout).post {
            // The bounds for the delegate view, which is an ImageButton in this
            // example.
            val delegateArea = Rect()
            val myButton = findViewById<ImageButton>(R.id.button).apply {
                isEnabled = true
                setOnClickListener {
                    Toast.makeText(
                            this@MainActivity,
                            "Touch occurred within ImageButton touch region.",
                            Toast.LENGTH_SHORT
                    ).show()
                }

                // The hit rectangle for the ImageButton.
                getHitRect(delegateArea)
            }

            // Extend the touch area of the ImageButton beyond its bounds on the
            // right and bottom.
            delegateArea.right += 100
            delegateArea.bottom += 100

            // Set the TouchDelegate on the parent view so that touches within
            // the touch delegate bounds are routed to the child.
            (myButton.parent as? View)?.apply {
                // Instantiate a TouchDelegate. "delegateArea" is the bounds in
                // local coordinates of the containing view to be mapped to the
                // delegate view. "myButton" is the child view that receives
                // motion events.
                touchDelegate = TouchDelegate(delegateArea, myButton)
            }
        }
    }
}

Java

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Get the parent view.
        View parentView = findViewById(R.id.parent_layout);

        parentView.post(new Runnable() {
            // Post in the parent's message queue to make sure the parent lays
            // out its children before you call getHitRect().
            @Override
            public void run() {
                // The bounds for the delegate view, which is an ImageButton in
                // this example.
                Rect delegateArea = new Rect();
                ImageButton myButton = (ImageButton) findViewById(R.id.button);
                myButton.setEnabled(true);
                myButton.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Toast.makeText(MainActivity.this,
                                "Touch occurred within ImageButton touch region.",
                                Toast.LENGTH_SHORT).show();
                    }
                });

                // The hit rectangle for the ImageButton.
                myButton.getHitRect(delegateArea);

                // Extend the touch area of the ImageButton beyond its bounds on
                // the right and bottom.
                delegateArea.right += 100;
                delegateArea.bottom += 100;

                // Instantiate a TouchDelegate. "delegateArea" is the bounds in
                // local coordinates of the containing view to be mapped to the
                // delegate view. "myButton" is the child view that receives
                // motion events.
                TouchDelegate touchDelegate = new TouchDelegate(delegateArea,
                        myButton);

                // Set the TouchDelegate on the parent view so that touches
                // within the touch delegate bounds are routed to the child.
                if (View.class.isInstance(myButton.getParent())) {
                    ((View) myButton.getParent()).setTouchDelegate(touchDelegate);
                }
            }
        });
    }
}