Members of a singleTop activity in background are finalized

[georgivzh]

Steps to Reproduce

1. Create an activity with a singleTop launch mode and add a class member of type ObservableCollection or LruCache.

2. Create a second activity with a parent the first activity.

3. Run the app and from the first activity (which is the main activity) start the second activity.

4. Now do some resource consumption operation as loading a bitmap.

The result is JavaFinalize() is called on the member of the first activity while the second activity is displayed and the first is in background. This is not acceptable! The instance of the first activity is still alive, but some members are disposed (Java.Lang.Object Handle becomes null). When I return back to the first activity that member is already disposed (OnCreate is not called because of the singleTop mode).

Expected Behavior

All members of the first activity should be alive.

Actual Behavior

Some of the members of the first activity are disposed.

Version Information

Xamarin Android SDK 8.3.3.2.

Reproduced on a real device (LG G4C) running Android API 23.

Visual Studio Community version 15.7.5.

[georgivzh]

I found a solution which I don't know if it is a good one, but it works for me. It seems that the activity in background is not referenced by anything, so this exposes all of its members to the risk of garbage collection. My solution is to make a reference to the activity which is going to stay in background (singleTop launch mode). In my application I have a common singleton class where I keep a shared logic, so I added to it a new member to which I will assign my activity when it is going in background. When activity is brought back to the user, I will remove the reference:

var intent = new Intent(this, typeof(CImageActivity));

intent.PutExtra(CImageActivity.IMAGE_URI, imageUri);

StartActivity(intent);

// The interesting part is here. this is a pointer to the activity that will be in background.
// CApplication is a singleton class.
CApplication.Instance.ActivityStrongReference = this;

[JRE-6783]

Are you sure it is just singleTop launch mode and not standard too?

[georgivzh]

Yes, I am. These are all of my attributes:
[Activity(ParentActivity = typeof(CAllMessagesActivity), LaunchMode = Android.Content.PM.LaunchMode.SingleTop)]

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