触摸事件
两种检测触摸事件的方式:
设置触摸监听 setOnTouchListener
返回 true: 表示消费事件 , 可以检测到 down/move/up 事件返回 false: 不消费事件, 只能检测到 down 事件
重写onTouchEvent()必须继承自系统的一个View,才能重写 onTouchEvent()方法;如 MyImageView extends ImageView ,才能重写onTouchEvent返回 true: 消费事件,能检测到 down/move/up 事件返回 false: 不消费事件,只能检测到 down 事件
如果两种触摸事件都存在,并且都返回true,结果如何?
setOnTouchListener 有效onTouchEvent() 无效
另外:一个View能否消费事件,关键看 dispatchTouchEvent(),我们来看下 android-10的源码(为什么要看这个版本的源码呢?因为低版本的源码中,原理性的知识点都是一样的,高版本的源码中,加入了非常多的逻辑判断)View.java事件是怎么分发的
/*** Pass the touch screen motion event down to the target view, or this* view if it is the target.** @param event The motion event to be dispatched.* @return True if the event was handled by the view, false otherwise.*/public boolean dispatchTouchEvent(MotionEvent event) {if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&mOnTouchListener.onTouch(this, event)) {return true;}return onTouchEvent(event);}
我们可以看到如果两种方式都设置的话,每次这个if条件判断都会走,所以 onTouchListener 可以拿到所有事件(down/move/up事件);只有onTouchListener返回false时,onTouchEvent()方法才会走,才能拿到(down/move/up)所有事件;
如何让两种方式同时生效呢?
setOnTouchListener 返回false onTouchEvent() 返回true
下面我们上代码:
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="/apk/res/android"xmlns:tools="/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context="com.xialm.touchdemo.MainActivity"><ImageViewandroid:id="@+id/iv"android:layout_width="100dp"android:layout_height="100dp"android:src="@mipmap/ic_launcher" /></RelativeLayout>
修改返回true,所有事件都能拿到;返回false,只能拿到down事件;
true时:
04-28 01:44:13.515 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 004-28 01:44:18.266 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:44:18.283 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:44:18.333 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:44:19.555 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 1
false时:
04-28 01:44:13.515 1471-1471/com.xialm.touchdemo E/MainActivity: onTouch: 0
同理,我们创建 CustomImageView,继承自ImageView,同时修改布局文件中的ImageView为 CustomImageView
public class CustomImageView extends ImageView {private static final String TAG = "CustomImageView";public CustomImageView(Context context) {super(context);}public CustomImageView(Context context, AttributeSet attrs) {super(context, attrs);}public CustomImageView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}/*** 返回false:只能拿到down事件* 返回true: 能拿到down/move/up事件* @param event* @return*/@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.e(TAG, "onTouchEvent: "+event.getAction() );return true; //super.onTouchEvent(event);}}
同时设置,同时返回true的情况,可以看到跟我们的分析是一样的
04-28 01:47:54.060 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 004-28 01:47:54.434 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:47:54.450 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:47:54.817 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:47:54.850 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:47:55.188 5005-5005/com.xialm.touchdemo E/MainActivity: onTouch: 1
同时设置setOnTouchListener返回false,onTouchEvent()返回true
04-28 01:49:55.452 6978-6978/com.xialm.touchdemo E/MainActivity: onTouch: 004-28 01:49:55.452 6978-6978/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 004-28 01:49:58.850 6978-6978/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:49:58.850 6978-6978/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 01:49:58.866 6978-6978/com.xialm.touchdemo E/MainActivity: onTouch: 204-28 01:49:58.866 6978-6978/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 01:49:59.926 6978-6978/com.xialm.touchdemo E/MainActivity: onTouch: 104-28 01:49:59.926 6978-6978/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 1
Touch事件处理流程分析
我们自定义一个MyLinearLayout 继承自系统的LinearLayout,然后在布局文件中包裹 CustomImageView,
public class MyLinearLayout extends LinearLayout {private static final String TAG = "MyLinearLayout";public MyLinearLayout(Context context) {super(context);}public MyLinearLayout(Context context, AttributeSet attrs) {super(context, attrs);}public MyLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.e(TAG, "onTouchEvent: "+event.getAction() );return true;//super.onTouchEvent(event); 返回true}}
<com.xialm.touchdemo.MyLinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:background="#ccc"android:padding="10dp"><com.xialm.touchdemo.CustomImageViewandroid:id="@+id/iv"android:layout_width="100dp"android:layout_height="100dp"android:src="@mipmap/ic_launcher" /></com.xialm.touchdemo.MyLinearLayout>
我们只研究onTouchEvent()
CustomImageView的onTouchEvent()也返回true
04-28 02:37:15.952 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 004-28 02:37:16.350 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:37:16.367 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:37:16.700 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:37:17.367 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:37:17.648 14101-14101/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 1
当父View和子view都有处理触摸事件的逻辑时,子view可以接收到所有的事件;
这是因为事件传递是由外向内,而事件的消费是由内向外的;
只有子View不处理触摸事件时,父View才能处理消费事件(即CustomImageView的onTouchEvent()返回false,MyLinearLayout的onTouchEvent()返回true)
使用下面示意图来解释,再好不过了:
父View想要消费事件,有没有办法呢?办法是有的,只需重写onInterceptTouchEvent()方法,返回true,把事件中断掉,则事件就不能往下传递了,我们处理消费逻辑即可:
public class CustomImageView extends ImageView {...省略代码.../*** 返回false:只能拿到down事件* 返回true: 能拿到down/move/up事件* @param event* @return*/@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.e(TAG, "onTouchEvent: "+event.getAction() );return true; //super.onTouchEvent(event);}}
public class MyLinearLayout extends LinearLayout {...省略代码...private int count = 0;@Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {count++;if (count > 4) {return true;}return false; // 中断事件}@Overridepublic boolean onTouchEvent(MotionEvent event) {Log.e(TAG, "onTouchEvent: "+event.getAction() );return true;//super.onTouchEvent(event);}}
04-28 02:52:30.948 28332-28332/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 004-28 02:52:31.250 28332-28332/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:52:31.266 28332-28332/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:52:31.783 28332-28332/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 204-28 02:52:31.800 28332-28332/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 304-28 02:52:31.867 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:31.933 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:31.950 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:32.033 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:32.050 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:32.167 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 204-28 02:52:35.396 28332-28332/com.xialm.touchdemo E/MyLinearLayout: onTouchEvent: 1由下面流程示意图来说明:
触摸事件与点击事件
onTouchEvent() 与 onClickListener点击事件是由 down 和 up 事件组成的,系统一直检测 up事件是否发生,如果有up事件,就会判断 onClickListener监听是否存在,存在就回调onClick()方法触摸事件和点击事件同时存在时:
系统是怎么区分点击事件还是触摸事件呢?不知道你有没有注意到我们重写onTouchEvent()时有一句话
super.onTouchEvent(event); // 在内部处理了,点击事件的逻辑
查看android-10 View.java源码 我们着重留意一下 up事件
/*** Implement this method to handle touch screen motion events.** @param event The motion event.* @return True if the event was handled, false otherwise.*/public boolean onTouchEvent(MotionEvent event) {final int viewFlags = mViewFlags;if ((viewFlags & ENABLED_MASK) == DISABLED) {// A disabled view that is clickable still consumes the touch// events, it just doesn't respond to them.return (((viewFlags & CLICKABLE) == CLICKABLE ||(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));}if (mTouchDelegate != null) {if (mTouchDelegate.onTouchEvent(event)) {return true;}}if (((viewFlags & CLICKABLE) == CLICKABLE ||(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {switch (event.getAction()) {case MotionEvent.ACTION_UP: // 着重研究up事件if ((mPrivateFlags & PRESSED) != 0) {// take focus if we don't have it already and we should in// touch mode.boolean focusTaken = false;if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {focusTaken = requestFocus();}if (!mHasPerformedLongPress) {// This is a tap, so remove the longpress checkif (mPendingCheckForLongPress != null) {removeCallbacks(mPendingCheckForLongPress);}// Only perform take click actions if we were in the pressed stateif (!focusTaken) {performClick(); // 执行点击监听回调}}if (mUnsetPressedState == null) {mUnsetPressedState = new UnsetPressedState();}if (!post(mUnsetPressedState)) {// If the post failed, unpress right nowmUnsetPressedState.run();}}break;case MotionEvent.ACTION_DOWN:mPrivateFlags |= PRESSED;refreshDrawableState();if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {postCheckForLongClick();}break;case MotionEvent.ACTION_CANCEL:mPrivateFlags &= ~PRESSED;refreshDrawableState();break;case MotionEvent.ACTION_MOVE:final int x = (int) event.getX();final int y = (int) event.getY();// Be lenient about moving outside of buttonsint slop = ViewConfiguration.get(mContext).getScaledTouchSlop();if ((x < 0 - slop) || (x >= getWidth() + slop) ||(y < 0 - slop) || (y >= getHeight() + slop)) {// Outside buttonif ((mPrivateFlags & PRESSED) != 0) {// Remove any future long press checksif (mPendingCheckForLongPress != null) {removeCallbacks(mPendingCheckForLongPress);}// Need to switch from pressed to not pressedmPrivateFlags &= ~PRESSED;refreshDrawableState();}} else {// Inside buttonif ((mPrivateFlags & PRESSED) == 0) {// Need to switch from not pressed to pressedmPrivateFlags |= PRESSED;refreshDrawableState();}}break;}return true;}return false;}
/*** Call this view's OnClickListener, if it is defined.** @return True there was an assigned OnClickListener that was called, false* otherwise is returned.*/public boolean performClick() {sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);if (mOnClickListener != null) { // 点击监听回调不为null,就执行回调,并返回trueplaySoundEffect(SoundEffectConstants.CLICK);mOnClickListener.onClick(this);return true;}return false;}如果我们想要同时处理点击事件和触摸事件,super.onTouchEvent(event); 就不可少
@Overridepublic boolean onTouchEvent(MotionEvent event) {super.onTouchEvent(event);Log.e(TAG, "onTouchEvent: "+event.getAction() );return true;}
04-28 03:40:08.296 8330-8330/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 004-28 03:40:08.392 8330-8330/com.xialm.touchdemo E/CustomImageView: onTouchEvent: 104-28 03:40:08.393 8330-8330/com.xialm.touchdemo E/MainActivity: onClick:
