I am trying to handle the touch event for View that is added in the WindowManager using:
WindowManager.addView(View, LayoutParams).
Call that view is MyView. This view has 2 part, 1 that is clickable and the other is not
What I want is when user touchs the clickable part then the MyView will handle the touch event. If user touches the unclickable part, then the event will send through like there is no MyView there.
What I have tried is when user touch the clickable part I update the layout params flag to NOT_FOCUSABLE, then the touch event is handled by MyView.
When user touch the unclickable part, I set the layout params flag to NOT_TOUCHABLE, then the touch event is sent to underneath content. But this time, MyView is no long receive the touch event due to this layout params flag, so I have no chance to reset the flag.
I have no idea to address the problem. Anyone has an idea, please share. Thanks
I think, you need to add root ViewGroup (e.g. FrameLayout) into the your windowManager. Then, add all views you need to show into the root. Root will consume all touch events and send them to the child views.
Sorry if I made some mistakes - English isn't my native language.
I am having a gesture listener attached to a view and I have onSingleTap Event handled.
It handles it properly if I tap anywhere in the view. But say if the View is having any subview and if I am tapping the subview the event does not get triggered.
Is there a way to pass this touch from child to parent? And also the children contains BUTTONS. so if the press is on a child button it should not pass the touch to parent. Otherwise it must pass it to parent. Anyway to achieve this?
You can override the Activity's dispatchTouchEvent(MotionEvent) in order to handle the dispatching yourself.
A good handling would be to first check if it triggers the gesture in your view and if not just call super.dispatchTouchEvent(MotionEvent);
The one thing you have to care about while doing this is to keep the gestures coherent with the rest of the platform.
The problem is the the scrolling will intercept with touch event has set to the parent layout.
Can I keep the onTouch event with the scroll in ScrollView ?
This is a very tricky part. There is an overriden method from Activity which is: public boolean onTouchEvent(MotionEvent event)
This is the general method that interprets all the touch events from the whole screen. And you could say, "ok, I can implement this and I am good to go..". And here comes the difficult part on how android works.
As you know every View has its own onTouchEvent() method that you could implement in order to add some custom implementation. So which method will listen? The ScrollView or the Activity? It appears that these touch events go from the "inside" elements to the "outside" elements. I mean parent-child relations.
Another thing to take into account is that the onTouchEvent method returns a boolean. This boolean parameter determines whether the touch event should go one level up or it is handled by the current View. Meaning that if you have a CustomViewA that implements the onTouchEvent() and CustomViewB implementing its own touch event, and the A is a child in B then the touch event would go through A first and if it is not handled it would go to B.
So basically yes it could be done. It depends on what touch event you wanted to do.
So in our case, the ScrollView returns true when the touch events are a horizontal. The activity's touch event will be handled only if the ScrollView touch event is not handled by itself then you are fine. Otherwise you have to override and implement the on touch event of scroll view and in some cases you have to return false so as for the whole layout to implement it. Good luck with the last part. I started to implement a fling effect but came up with some difficulties so I have implemented a 2 finger move with scroll view in it and it works like a charm.
This is about a week of research and experimenting and it is an overview of what I came up with. if you find anything else please let me know. Hope it helped.
I'm not asking how to handle touch events, but what is going on behind the scenes? If there are several nested widgets, what order do they see the events in? Does the developer have any control over it? Ideally I would like a document on the subject.
Let's take a look at a visual example.
When a touch event occurs, first everyone is notified of the event, starting at the Activity and going all the way to the view on top. Then everyone is given a chance to handle the event, starting with the view on top (view having highest Z order in the touch region) and going all the way back to the Activity. So the Activity is the first to hear of it and the last to be given a chance to handle it.
If some ViewGroup wants to handle the touch event right away (and not give anyone else down the line a chance at it) then it can just return true in its onInterceptTouchEvent(). An Activity doesn't have onInterceptTouchEvent() but you can override dispatchTouchEvent() to do the same thing.
If a View (or a ViewGroup) has an OnTouchListener, then the touch event is handled by OnTouchListener.onTouch(). Otherwise it is handled by onTouchEvent(). If onTouchEvent() returns true for any touch event, then the handling stops there. No one else down the line gets a chance at it.
More detailed explanation
The above diagram makes things a little more simple than they actually are. For example, between the Activity and ViewGroup A (the root layout) there is also the Window and the DecorView. I left them out above because we generally don't have to interact with them. However, I will include them below. The description below follows a touch event through the source code. You can click a link to see the actual source code.
(Update: the source code has been updated so the line numbers are off now, but clicking the links will still get you to the right file. Just do a search for the method name.)
The Activity's dispatchTouchEvent() is notified of a touch event. The touch event is passed in as a MotionEvent, which contains the x,y coordinates, time, type of event, and other information.
The touch event is sent to the Window's superDispatchTouchEvent(). Window is an abstract class. The actual implementation is PhoneWindow.
The next in line to get the notification is DecorView's superDispatchTouchEvent(). DecorView is what handles the status bar, navigation bar, content area, etc. It is actually just a FrameLayout subclass, which is itself a subclass of ViewGroup.
The next one to get the notification (correct me if I'm wrong) is the content view of your activity. That is what you set as the root layout of your activity in xml when you create the layout in the Android Studio's Layout Editor. So whether you choose a RelativeLayout, a LinearLayout, or a ConstraintLayout, they are all subclasses of ViewGroup. And ViewGroup gets notified of the touch event in dispatchTouchEvent(). This is the ViewGroup A in my diagrams above.
The ViewGroup will notify any children it has of the touch event, including any ViewGroup children. This is ViewGroup B in my diagrams above.
Anywhere along the way, a ViewGroup can short-circuit the notification process by returning true for onInterceptTouchEvent().
Assuming no ViewGroup cut the notifications short, the natural end of the line for the notifications is when the View's dispatchTouchEvent() get's called.
Now it is time, to start handling the events. If there is an OnTouchListener, then it gets the first chance at handling the touch event with onTouch(). Otherwise, the View's onTouchEvent() gets to handle it.
Now all the ViewGroups recursively up the line get a chance to handle the touch event in the same way that View did. Although, I didn't indicate this in the diagram above, a ViewGroup is a View subclass, so everything I described about OnTouchListener.onTouch() and onTouchEvent() also applies to ViewGroups.
Finally, if no one else wanted it, the Activity also gets the last chance to handle the event with onTouchEvent().
FAQ
When would I ever need to override dispatchTouchEvent()?
Override it in the Activity if you want to catch a touch event before any of the views get a chance at it. For a ViewGroup (including the root view), then just override onInterceptTouchEvent() and onTouchEvent().
When would I ever need to override onInterceptTouchEvent()?
If you just want to spy of the touch notifications that are coming in, you can do it here and return false.
However, the main purpose of overriding this method is to let the ViewGroup handle a certain type of touch event while letting the child handle another type. For example, a ScrollView does this to handle scrolling while letting its child handle something like a Button click. Conversely, if the child view doesn't want to let its parent steal its touch event, it can call requestDisallowTouchIntercept().
What are the touch event types?
The main ones are
ACTION_DOWN - This is the start of a touch event. You should always return true for the ACTION_DOWN event in onTouchEvent if you want to handle a touch event. Otherwise, you won't get any more events delivered to you.
ACTION_MOVE - This event is continuously fired as you move your finger across the screen.
ACTION_UP - This is the last event of a touch event.
A runner up is ACTION_CANCEL. This gets called if a ViewGroup up the tree decides to intercept the touch event.
You can view the other kinds of MotionEvents here. Since Android is multi-touch, events are also fired when other fingers ("pointers") touch the screen.
Further study
Android onTouchEvent Part 1, Part 2, and Part 3 (YouTube video - good summary of some of the links below)
Mastering the Android Touch System (thorough video by Google developer)
Android UI Internal : Pipeline of View's Touch Event Handling
Managing Touch Events in a ViewGroup (Android docs)
Input Events (Android docs)
Gestures and Touch Events
From Activity viewpoint:
Touch events are delivered first to Activity.dispatchTouchEvent. It's where you may catch them first.
Here they get dispatched to Window, where they traverse View hierarchy, in such order that Widgets that are drawn last (on top of other widgets) have chance to process touch in View.onTouchEvent first. If some View returns true in onTouchEvent, then traversal stops and other Views don't receive touch event.
Finally, if no View consumes touch, it's delivered to Activity.onTouchEvent.
That's all your control. And it's logical that what you see drawn on top of something else, has chance to process touch event before something drawn below it.
Android Touch event
I have prepared a high level diagram that should illustrate a simple flow.
dispatchTouchEvent() - Activity, ViewGroup, View
onInterceptTouchEvent() - ViewGroup
onTouch() - ViewGroup, View. Using setOnTouchListener()
onTouchEvent() - Activity, ViewGroup, View
[iOS onTouch]
following Suragch's answer,
pseudocode:
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean consume = false;
if (onInterceptTouchEvent(ev) {
consume = onTouchEvent(ev);
} else {
consume = child.dispatchTouchEvent(ev);
}
return consume;
}
ref:Android开发艺术探索
We are developing an application where we need to capture MotionEvents from multiple views simultaneously. When we try to do so, Android only dispatches events to the first touched view and, when touching another view simultaneously, it gives us an ACTION_POINTER_DOWN on the first view only, even if the pointer coordinates are outside its bounds and inside the other views'.
Is there any way we can get events dispatched to every touched view (in separate calls to OnTouch)?
We believe intercepting the touch events from a parent view and then manually dispatching them to each view might work, but even if it does, it would not be practical for what we are trying to achieve. Is there an easier way?
At least Android 3.0 adds support for splitting touch events between multiple Views.
Split touch events is enabled by default when AndroidManifest <uses-sdk> defines either android:minSdkVersion="11" or android:targetSdkVersion="11". For explanation See android:splitMotionEvents and android:windowEnableSplitTouch
Touch event is first catched by the view currently in focus. If you touched 1 view and have "consumed" event and are working with it, any other events will be dispatched to this view, no matter where you click.
If you return false from your touchListener (thus saying that event is not consumed) it will be delegated down to other views, but on another separate click new event will be dispatched to other view.
http://www.zdnet.com/blog/burnette/how-to-use-multi-touch-in-android-2-part-3-understanding-touch-events/1775
http://developer.android.com/guide/topics/ui/ui-events.html
While this should work automatically with Android SDK 11+, it wasn't working for my app. I was trying to capture touches in a main view, plus some views that were subviews of the main view; in that case, touches were only captured by the view "level" that received the first touch. I reorganized my view structure so that all the views were siblings and now they are capturing events as expected.