在
ViewGroup
会特别照料
因为在 ViewGroup
中,子项是不同位置的子项很常见
与 ViewGroup
本身相比。为了确保每个视图都能正确接收
触摸事件,可替换
onInterceptTouchEvent()
方法。
请参阅以下相关资源:
在 ViewGroup 中拦截轻触事件
每当在以下事件中检测到触摸事件时,系统都会调用 onInterceptTouchEvent()
方法:
ViewGroup
的表面,包括其子级的表面。如果
onInterceptTouchEvent()
会返回 true
,即
MotionEvent
会拦截,这意味着不会将其传递给子元素,而是传递给
onTouchEvent()
方法。
onInterceptTouchEvent()
方法让父级有机会查看触摸事件
先于其子项执行此操作。如果您从onInterceptTouchEvent()
退回 true
,
之前处理触摸事件的子视图会收到
ACTION_CANCEL
,
并且从该时间点开始的事件会发送到父级的 onTouchEvent()
方法
进行常规处理onInterceptTouchEvent()
还可以返回 false
和
在事件沿视图层次结构向下移动至其常用目标时监视事件,这些目标负责处理
事件使用自己的 onTouchEvent()
。
在以下代码段中,MyViewGroup
类扩展了 ViewGroup
。
MyViewGroup
包含多个子视图。如果您用手指在子视图上拖动
在水平方向上,子视图不再获取轻触事件,而 MyViewGroup
负责处理轻触事件
滚动其内容来触发事件。但是,如果您在儿童视图中点按按钮,或滚动
则父视图不会拦截这些触摸事件,因为子视图是所需的
目标。在这种情况下,onInterceptTouchEvent()
会返回 false
,而
未调用 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。ViewGroup
当子元素不需要父元素及其
祖先实体通过 onInterceptTouchEvent()
拦截触摸事件。
处理 ACTION_OUTSIDE 事件
如果 ViewGroup
收到 MotionEvent
和
ACTION_OUTSIDE
,
默认情况下,系统不会将该事件分派给其子项。要使用以下代码处理 MotionEvent
:
ACTION_OUTSIDE
,任一替换项
dispatchTouchEvent(MotionEvent event)
分派给相应的 View
或
在相关的
Window.Callback
- 用于
示例 Activity
。
使用 ViewConfiguration 常量
上述代码段使用当前的 ViewConfiguration
来初始化变量
名为 mTouchSlop
。您可以使用 ViewConfiguration
类来访问
Android 系统常用的距离、速度和时间。
“Touch slop”是指在做出相应手势之前,用户触摸可移动的距离(以像素为单位) 解释为滚动。Touch slop 通常用于防止在用户使用设备时 正在执行另一项触摸操作,例如触摸屏幕上的元素。
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快滑测量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,使其成为
允许父项将子视图的可触摸区域扩展到子视图的边界之外。本次
在子视图必须很小但需要更大的触摸区域时非常有用。您还可以使用
来缩小子元素的触摸区域。
在以下示例中,
ImageButton
是 _delegate
view_ — 即父项扩展其触摸区域的子项。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>
以下代码段完成了这些任务:
- 获取父视图并发布
Runnable
在界面线程上执行这样可确保在调用getHitRect()
方法。getHitRect()
方法会获取子项的命中矩形(或者 可触摸区域)。 - 查找
ImageButton
子视图并调用getHitRect()
以获取 子元素的可触摸区域边界。 - 扩展
ImageButton
子视图点击矩形的边界。 - 实例化
TouchDelegate
,传入展开的点击矩形和ImageButton
个子视图作为参数。 - 在父视图上设置
TouchDelegate
,以便在触摸委托内进行轻触 均将边界发送到子对象
就 ImageButton
子视图的轻触代理而言,父视图
并接收所有触摸事件如果触摸事件发生在子视图的点击矩形内,则父视图
将触摸事件传递给子视图进行处理。
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); } } }); } }