public
boolean
onInterceptTouchEvent
(MotionEvent
ev)
Since: API
Level 1
Implement this method to
intercept all touch screen motion events. This
allows you to watch events as they are dispatched to your children, and
take ownership of the current gesture at any point.
Using this function takes some care, as it has a fairly
complicated
interaction with View.onTouchEvent(MotionEvent)
,
and using it requires implementing
that method as well as this one in the correct way. Events will be
received in the following order:
- You will receive the down event here.
- The down event will be handled either by a child of this view
group, or given to your own onTouchEvent() method to handle; this means
you should implement onTouchEvent() to return true, so you will
continue to see the rest of the gesture (instead of looking for
a parent view to handle it). Also, by returning true from
onTouchEvent(), you will not receive any following
events in onInterceptTouchEvent() and all touch processing must
happen in onTouchEvent() like normal. - For as long as you return false from this function, each
following
event (up to and including the final up) will be delivered first here
and then to the target's onTouchEvent(). - If you return true from here, you will not receive any
following events: the target view will receive the same event but
with the actionACTION_CANCEL
,
and all further
events will be delivered to your onTouchEvent() method and no longer
appear here.
Parameters
ev | The motion event being dispatched down the hierarchy. |
---|
Returns
- Return true to steal motion events from the
children and have
them dispatched to this ViewGroup through onTouchEvent().
The current target will receive an ACTION_CANCEL event, and no further
messages will be delivered here. -
-
-
-
-
onInterceptTouchEvent
和
onTouchEvent
调用时序onInterceptTouchEvent()
是
ViewGroup
的一个方法,目的是在系统向该
ViewGroup
及其各个
childView
触发
onTouchEvent()
之前对相关事件进行一次拦截,
Android
这么设计的想法也很好理解,由于
ViewGroup
会包含若干
childView,
因此需要能够统一监控各种
touch
事件的机会,因此纯粹的不能包含子
view
的控件是没有这个方法的,如
LinearLayout
就有,
TextView
就没有。
onInterceptTouchEvent()
使
用也很简单,如果在
ViewGroup
里覆
写了该方法,那么就可以对各种
touch
事
件加以拦截。但是如何拦截,是否所有的
touch
事
件都需要拦截则是比较复杂的,
touch
事
件在
onInterceptTouchEvent()
和
onTouchEvent
以及各个
childView
间的传递机制完全取决于
onInterceptTouchEvent()
和
onTouchEvent()
的返回值。并且,针对
down
事件处理的返回值直接影响到后续
move
和
up
事
件的接收和传递。
关于返回值的问题,基本规则很清楚,如果
return true,
那么表示该方法消费了此次事件,如果
return false
,那么表示该方法并未处理完全,该事件仍然
需要以某种方式传递下去继续等待处理。
SDK
给
出的说明如下:
·
You will receive
the down event here.·
The down event
will be handled either by a child of this view group, or given to your
own onTouchEvent() method to handle; this means you should implement
onTouchEvent() to return true, so you will continue to see the rest of
the gesture (instead of looking for a parent view to handle it). Also,
by returning true from onTouchEvent(), you will not receive any
following events in onInterceptTouchEvent() and all touch processing
must happen in onTouchEvent() like normal.·
For as long as you
return false from this function, each following event (up to and
including the final up) will be delivered first here and then to the
target's onTouchEvent().·
If you return true from here, you will not receive any
following events: the target view will receive the same event but with
the action
ACTION_CANCEL
, and all further events will be delivered to your
onTouchEvent() method and no longer appear here.
由于
onInterceptTouchEvent()
的
机制比较复杂,上面的说明写的也比较复杂,总结一下,基本的规则是:
1.
down
事件首先会传递到
onInterceptTouchEvent()
方法
2.
如
果该
ViewGroup
的
onInterceptTouchEvent()
在接收到
down
事件处理完成之后
return false
,那么后续的
move, up
等事件将继续会先传递给该
ViewGroup
,之后才和
down
事件一样传递给最终的目标
view
的
onTouchEvent()
处
理。
3.
如
果该
ViewGroup
的
onInterceptTouchEvent()
在接收到
down
事件处理完成之后
return true
,那么后续的
move, up
等事件将不再传递给
onInterceptTouchEvent()
,而是和
down
事件一样传递给该
ViewGroup
的
onTouchEvent()
处理,注意,目标
view
将接收不到任何事件。
4.
如
果最终需要处理事件的
view
的
onTouchEvent()
返回了
false
,那么该事件将被传递至其上一层次的
view
的
onTouchEvent()
处
理。
5.
如
果最终需要处理事件的
view
的
onTouchEvent()
返回了
true
,那么后续事件将可以继续传递给该
view
的
onTouchEvent()
处
理。
下面用一个简单的实验说明上述复杂的规则。视图自底向上共
3
层,其中
LayoutView1
和
LayoutView2
就
是
LinearLayout
,
MyTextView
就是
TextView
:
对应的
xml
布
局文件如下:
<?
xml
version
=
"1.0"
encoding
=
"utf-8"
?>
<
com.touchstudy.LayoutView1
xmlns:android
=
"http://schemas.android.com/apk/res/android"
android:orientation
=
"vertical"
android:layout_width
=
"fill_parent"
android:layout_height
=
"fill_parent"
>
<
com.touchstudy.LayoutView2
android:orientation
=
"vertical"
android:layout_width
=
"fill_parent"
android:layout_height
=
"fill_parent"
android:gravity
=
"center"
>
<
com.touchstudy.MyTextView
android:layout_width
=
"wrap_content"
android:layout_height
=
"wrap_content"
android:id
=
"@+id/tv"
android:text
=
"AB"
android:textSize
=
"40sp"
android:textStyle
=
"bold"
android:background
=
"#FFFFFF"
android:textColor
=
"#0000FF"
/>
</
com.touchstudy.LayoutView2
></
com.touchstudy.LayoutView1
>
下面看具体情况:
1.
onInterceptTouchEvent()
处
理
down
事
件均返回
false
,
onTouchEvent()
处
理事件均返回
true
------------------------------------------------------------------------------------------------------------------------------
04-11 03:58:42.620:
DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:58:42.620:
DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:58:42.620:
DEBUG/MyTextView(614): onTouchEvent action:ACTION_DOWN
04-11 03:58:42.800:
DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_MOVE
04-11 03:58:42.800:
DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_MOVE
04-11 03:58:42.800:
DEBUG/MyTextView(614): onTouchEvent action:ACTION_MOVE
…… //
省
略过多的
ACTION_MOVE
04-11 03:58:43.130:
DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_UP
04-11 03:58:43.130:
DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_UP
04-11 03:58:43.150:
DEBUG/MyTextView(614): onTouchEvent action:ACTION_UP
------------------------------------------------------------------------------------------------------------------------------
这是最常见的情况,
onInterceptTouchEvent
并
没有做任何改变事件传递时序的操作,效果上和没有覆写该方法是一样的。可以看到,各种事件的传递本身是自底向上的,次序是:
LayoutView1->LayoutView2->MyTextView
。注
意,在
onInterceptTouchEvent
均
返回
false
时,
LayoutView1
和
LayoutView2
的
onTouchEvent
并不会
收到事件
,而是最终传递给了
MyTextView
。
2.
LayoutView1
的
onInterceptTouchEvent()
处
理
down
事
件返回
true
,
MyTextView
的
onTouchEvent()
处
理事件返回
true
------------------------------------------------------------------------------------------------------------------------------
04-11 03:09:27.589:
DEBUG/LayoutView1(446): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:09:27.589:
DEBUG/LayoutView1(446): onTouchEvent action:ACTION_DOWN
04-11 03:09:27.629:
DEBUG/LayoutView1(446): onTouchEvent action:ACTION_MOVE
04-11 03:09:27.689:
DEBUG/LayoutView1(446): onTouchEvent action:ACTION_MOVE
…… //
省
略过多的
ACTION_MOVE
04-11 03:09:27.959:
DEBUG/LayoutView1(446): onTouchEvent action:ACTION_UP
------------------------------------------------------------------------------------------------------------------------------
从
Log
可
以看到,由于
LayoutView1
在拦截
第一次
down
事件时
return true
,所以后续的事件(包括第一次的
down
)将由
LayoutView1
本
身处理,事件不再传递下去。
3.
LayoutView1
,
LayoutView2
的
onInterceptTouchEvent()
处
理
down
事
件返回
false
,
MyTextView
的
onTouchEvent()
处
理事件返回
false
LayoutView2
的
onTouchEvent()
处
理事件返回
true
----------------------------------------------------------------------------------------------------------------------------
04-11 09:50:21.147:
DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_DOWN
04-11 09:50:21.147:
DEBUG/LayoutView2(301): onInterceptTouchEvent action:ACTION_DOWN
04-11 09:50:21.147:
DEBUG/MyTextView(301): onTouchEvent action:ACTION_DOWN
04-11 09:50:21.147:
DEBUG/LayoutView2(301): onTouchEvent action:ACTION_DOWN
04-11 09:50:21.176:
DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_MOVE
04-11 09:50:21.176:
DEBUG/LayoutView2(301): onTouchEvent action:ACTION_MOVE
04-11 09:50:21.206:
DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_MOVE
04-11 09:50:21.217:
DEBUG/LayoutView2(301): onTouchEvent action:ACTION_MOVE
…… //
省
略过多的
ACTION_MOVE
04-11 09:50:21.486:
DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_UP
04-11
09:50:21.486: DEBUG/LayoutView2(301): onTouchEvent action:ACTION_UP
----------------------------------------------------------------------------------------------------------------------------
可以看到,由于
MyTextView
在
onTouchEvent()
中
return false
,
down
事件被传递给其父
view
,即
LayoutView2
的
onTouchEvent()
方法处理,由于在
LayoutView2
的
onTouchEvent()
中
return true
,所以
down
事件传递并没有上传到
LayoutView1
。注意,后续的
move
和
up
事件均被传递给
LayoutView2
的
onTouchEvent()
处
理,而没有传递给
MyTextView
。