How to get onTouchEvent, long click and context menu working together?

Question

In our application we have a custom view (that extends ImageView) and in it we handle the touch events to record data. I wanted to add context menu functionality to this view and followed the guidelines in the official Android documents.

The onTouchEvent code works fine by itself. The context menu code also works fine. However, if I add them both, the context menu code stops working. I found out that with both pieces of code added, onCreateContextMenu is never called, therefore context menu is never displayed.

According to my interpretation of the Android documentation, returning false from onTouchEvent indicates that the event is not consumed, so it should be used for further processing. For some reason, it is not happening here. I would appreciate if anybody can tell me what I am missing. BTW, the target is Nexus One running 2.3.4 ROM.

Here's the code for the onTouchEvent in the custom view:

public boolean onTouchEvent(MotionEvent event) 
{
    switch (event.getAction())
    {
        case  MotionEvent.ACTION_DOWN:
            // Add event coordinates to an arraylist
            break;
    }

    return false;
}

Thank you in advance for any help.

Answer 1

Elaborating on hackbod answer, you should probably have as last method statement return super.onTouchEvent(event);.

I guess that if you don't process the event, and if you don't invoke the default View behavior, than no one will do anything, and nothing will happen.

The point of return value might be for example to invoke some ancestor' default behavior, and let the derived class know if the ancestor processed the event or not.

After doing some search on Android Developers, referring to the topic override an existing callback method for the View here it says :

This allows you to define the default behavior for each event inside your custom View and determine whether the event should be passed on to some other child View.

Hence the main idea behind the return value is to let Android know whether the event should be passed down to child Views or not.

HTH

Edit:

Regarding the "directions" you mention in your comment, generally speaking (i.e. not only on Android) the UI event handling process goes on something like this:

At some point your derived custom control receives the event. In your event hook implementation, it's up to you whether to involve your ancestor's behavior or not. That's all you got regarding the class inheritance direction.

Then, there's the other direction, the one related to the UI controls hierarchy. Your custom control might be contained in one larger control container, and your control might as well contain other inner controls (textboxes, buttons, ...). Regarding this direction, if you declare not to process the event (returning false) then the UI event handling mechanism will pass the bucket to the containing (?) control (think the one on the background of yours).

Answer 2

Do not register for context menu in OnCreate(), do it in onTouch() before return true;

registerForContextMenu(View v);
openContextMenu(View v);
return true;

Answer 3

You could call, from your long click listener,

openContextMenu(View view)

http://developer.android.com/reference/android/app/Activity.html#openContextMenu(android.view.View)

Answer 4

I encounter similar problem recently. When I enable long clickable in RecyeclerView's child, the ACTION_DOWN event can't not be received in RecyclerView's onTouchEvent.

If I changed to RecyclerView's dispatchTouchEvent, I would works. The ACTION_DOWN event can be received.

Answer 5

Returning false tells the parent that you didn't consume the event. The default implementation of View implements touch handling for that view; if you want that to execute, you must call super.onTouchEvent(event);