此页面由 Cloud Translation API 翻译。

在 ViewGroup 中管理触摸事件

在 ViewGroup 中处理轻触事件时需要特别小心，因为 ViewGroup 通常会有子视图，而这些子视图是除 ViewGroup 本身以外的其他轻触事件的目标。为了确保每个视图都能够正确地接收专门发给它的轻触事件，请替换 onInterceptTouchEvent() 方法。

请参阅以下相关资源：

在 ViewGroup 中拦截轻触事件

只要在 ViewGroup 的 surface（包括其子视图的 surface）上检测到轻触事件，系统就会调用 onInterceptTouchEvent() 方法。如果 onInterceptTouchEvent() 返回 true，系统会拦截 MotionEvent，这意味着系统不会将其传递给子视图，而是传递给父视图的 onTouchEvent() 方法。

onInterceptTouchEvent() 方法可以让父视图有机会抢在子视图之前检测到轻触事件。如果您从 onInterceptTouchEvent() 返回 true，则之前处理轻触事件的子视图会收到 ACTION_CANCEL，并且从该时间点开始，事件会发送到父视图的 onTouchEvent() 方法以进行常规处理。onInterceptTouchEvent() 也可能会返回 false，并在事件按照视图层次结构传递至常规目标的过程中进行监视，而这些目标会使用自己的 onTouchEvent() 处理事件。

在以下代码段中，MyViewGroup 类扩展了 ViewGroup。MyViewGroup 包含多个子视图。如果您在子视图上横向拖动手指，则子视图不再获取轻触事件，而 MyViewGroup 通过滚动内容来处理轻触事件。不过，如果您点按子视图中的按钮，或纵向滚动子视图，则父视图不会拦截这些轻触事件，因为子视图是预期目标。在这些情况下，onInterceptTouchEvent() 会返回 false，并且系统不会调用 MyViewGroup 类的 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.
        ...
    }
}

请注意，ViewGroup 还提供了 requestDisallowInterceptTouchEvent() 方法。当子视图不想让父视图及其祖先视图使用 onInterceptTouchEvent() 拦截轻触事件时，ViewGroup 便会调用此方法。

处理 ACTION_OUTSIDE 事件

如果 ViewGroup 收到带有 ACTION_OUTSIDE 的 MotionEvent，则默认情况下系统不会将该事件发送给其子视图。如需使用 ACTION_OUTSIDE 处理 MotionEvent，可以替换 dispatchTouchEvent(MotionEvent event) 以将其发送给相应的 View，或在相关 Window.Callback（例如 Activity）中对其进行处理。

使用 ViewConfiguration 常量

上面的代码段使用当前 ViewConfiguration 初始化名为 mTouchSlop 的变量。您可以使用 ViewConfiguration 类来获取 Android 系统常用的距离、速度和时间。

“Touch slop”是指在系统将手势解读为滚动之前，用户的轻触手势可以滑动的距离（以像素为单位）。Touch slop 通常用于防止在用户执行其他轻触操作（例如轻触屏幕上的元素）时发生意外滚动。

另外两个常用的 ViewConfiguration 方法是 getScaledMinimumFlingVelocity() 和 getScaledMaximumFlingVelocity()。这两个方法会分别返回发起滑动的最小速度和最大速度，以像素/秒为单位。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.
    }
}

扩展子视图的可轻触区域

Android 提供了 TouchDelegate 类，让父视图能够将子视图的可轻触区域扩展到子视图的边界之外。当子视图必须较小，但需要较大的轻触区域时，此方法很有用。您也可以使用此方法缩小子视图的轻触区域。

在以下示例中，ImageButton 是“代理视图”（即，父视图将扩展其轻触区域的子视图）。其布局文件如下：

<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>

以下代码段会完成以下任务：

获取父视图，并在界面线程上发布 Runnable。这样可以确保父视图先对子视图进行布局，然后再调用 getHitRect() 方法。getHitRect() 方法以父视图坐标的形式获取子视图的点击矩形（或可轻触区域）。
查找 ImageButton 子视图并调用 getHitRect() 以获取子视图可轻触区域的边界。
扩展 ImageButton 子视图点击矩形的边界。
实例化 TouchDelegate，将扩展的点击矩形和 ImageButton 子视图作为参数传入。
在父视图上设置 TouchDelegate，以便将轻触代理边界内的轻触操作传递给子视图。

作为 ImageButton 子视图的轻触代理，父视图会收到所有轻触事件。如果轻触事件发生在子视图的点击矩形内，父视图会将轻触事件传递给子视图处理。

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);
                }
            }
        });
    }
}

在 ViewGroup 中管理触摸事件 使用集合让一切井井有条 根据您的偏好保存内容并对其进行分类。

在 ViewGroup 中拦截轻触事件

Kotlin

Java

处理 ACTION_OUTSIDE 事件

使用 ViewConfiguration 常量

Kotlin

Java

扩展子视图的可轻触区域

Kotlin

Java

在 ViewGroup 中管理触摸事件