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Question by jules43 · Oct 07, 2015 at 01:16 AM · androidcrashjava to c#

How do I use AndroidJavaProxy to add a listener to a MediaPlayer

I have an Android application that has a functional video player, and I want to use the AndroidJavaProxy to add an OnInfoListener.

 class OnInfoListener : AndroidJavaProxy
 {
     public OnInfoListener() : base("android.media.MediaPlayer$OnInfoListener") {}
     void onInfo(AndroidJavaObject mp, int what, int extra)
     {
     }
 }

I already have an AndroidJavaObject called mediaPlayer which I am able to call to play/pause the video, so I then do this:

 mediaPlayer.Call("setOnInfoListener", new OnInfoListener());

As soon as it reaches the point where this callback would be called it crashes the app out. I have tried to attach the debugger and trap the callback with mixed results, mostly it just crashes out.

I believe the callback comes from a different thread, is there any problem using AndroidJavaProxy with multiple threads?

Thanks

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avatar image jules43 · Oct 06, 2015 at 10:32 PM 0
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An alternative question might be how can I debug this?

avatar image jules43 · Oct 07, 2015 at 07:03 AM 0
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The code above seems to work fine if I attach a listener that doesn't take any arguments (such as OnPreparedListener). As soon as the listener takes arguments it crashes the app.

avatar image jules43 · Oct 07, 2015 at 08:41 AM 0
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I've managed to attach the debugger to trap the callback and it appears to consistently arrive in the onInfo function and then crash after it returns.

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Answer by jules43 · Oct 07, 2015 at 11:14 AM

The reason Unity is crashing is because the return type of the listener declared does not match the return type of the listener required. Change:

 void onInfo(AndroidJavaObject mp, int what, int extra)

to:

 bool onInfo(AndroidJavaObject mp, int what, int extra)

and it will fix the problem. Unity matches the signature ignoring return type and then crashes if the return type signature doesn't match.

It is also worth noting that these callbacks can be called from a separate thread and so things like file I/O can cause exceptions. Code executed within these callbacks must be thread safe.

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