在 ViewGroup 中处理触摸事件需要特别小心，因为 ViewGroup 通常包含作为不同触摸事件目标的子级，而不是 ViewGroup 本身。为了确保每个视图都正确接收为其准备的触摸事件，请重写 onInterceptTouchEvent() 方法。
请参阅以下相关资源
在 ViewGroup 中拦截触摸事件
每当在 ViewGroup 的表面（包括其子级的表面）上检测到触摸事件时，都会调用 onInterceptTouchEvent() 方法。如果 onInterceptTouchEvent() 返回 true，则 MotionEvent 将被拦截，这意味着它不会传递给子级，而是传递到父级的 onTouchEvent() 方法。
onInterceptTouchEvent() 方法使父级有机会在子级之前查看触摸事件。如果您从 onInterceptTouchEvent() 返回 true，则先前处理触摸事件的子视图将收到 ACTION_CANCEL，并且从那时起发生的事件将发送到父级的 onTouchEvent() 方法以进行常规处理。onInterceptTouchEvent() 也可以返回 false 并监视事件如何在视图层次结构中向下传递到其通常的目标，这些目标使用其自己的 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。如果您水平拖动手指穿过子视图，则子视图将不再获取触摸事件，并且 MyViewGroup 通过滚动其内容来处理触摸事件。但是，如果您点击子视图中的按钮或垂直滚动子视图，则父级不会拦截这些触摸事件，因为子级是预期的目标。在这些情况下，onInterceptTouchEvent() 返回 false，并且不会调用 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 还提供了一个 requestDisallowInterceptTouchEvent() 方法。ViewGroup 在子级不希望父级及其祖先使用 onInterceptTouchEvent() 拦截触摸事件时调用此方法。
处理 ACTION_OUTSIDE 事件
如果 ViewGroup 收到一个带有 ACTION_OUTSIDE 的 MotionEvent，则默认情况下不会将其分派给其子级。要处理带有 ACTION_OUTSIDE 的 MotionEvent，请重写 dispatchTouchEvent(MotionEvent event) 以分派到相应的 View 或在相关的 Window.Callback 中处理它，例如 Activity。
使用 ViewConfiguration 常量
前面的代码段使用当前 ViewConfiguration 初始化一个名为 mTouchSlop 的变量。您可以使用 ViewConfiguration 类访问 Android 系统使用的常见距离、速度和时间。
“触摸容差”是指用户触摸在被解释为滚动之前可以游荡的像素距离。触摸容差通常用于防止用户执行其他触摸操作（例如触摸屏幕元素）时意外滚动。
另外两个常用的 ViewConfiguration 方法是 getScaledMinimumFlingVelocity() 和 getScaledMaximumFlingVelocity()。这些方法分别返回以像素/秒为单位测量的启动抛掷的最小和最大速度。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.
}
}
扩展子视图的可触摸区域
Android 提供了 TouchDelegate 类，使父级能够将子视图的可触摸区域扩展到子视图边界之外。当子视图必须很小但需要更大的触摸区域时，这很有用。您还可以使用此方法缩小子视图的触摸区域。
在以下示例中，ImageButton 是_委托视图_，即父级扩展其触摸区域的子级。以下是布局文件
<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>
以下代码段完成了这些任务
- 获取父视图并在 UI 线程上发布
Runnable。这确保了父级在调用getHitRect()方法之前布局其子级。getHitRect()方法获取子级在父级坐标中的_命中矩形_（或可触摸区域）。 - 查找
ImageButton子视图并调用getHitRect()以获取子级可触摸区域的边界。 - 扩展
ImageButton子视图的命中矩形的边界。 - 实例化一个
TouchDelegate，并将扩展的命中矩形和ImageButton子视图作为参数传递。 - 在父视图上设置
TouchDelegate，以便触摸委托边界内的触摸被路由到子级。
作为 ImageButton 子视图的触摸委托，父视图接收所有触摸事件。如果触摸事件发生在子级的命中矩形内，则父级将触摸事件传递给子级进行处理。
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);
}
}
});
}
}