Main Activity is not garbage collected after destruction because it is referenced by InputMethodManager indirectly

Question

I followed "Avoiding Memory Leaks" article from here.

However the proposed solution does not solve the leak problem. I tested this with android emulator on Windows XP (SDK 2.3.1). I dumped the heap and checked the main activity is still in the heap (I used MAT)

Here's what I did:

1. create HelloWorld app with HelloWorldActivity (it has no child views)
2. run Emulator and launch HelloWorld app.
3. close it by clicking back-key.
4. Cause gc in DDMS and dump heap <-- Here I found HelloWorldActivity instance.
5. 'Path to GC Roots' from it shows the following path.

HelloWorldActivity <- PhoneWindow$DecorView <- InputMethodManager

InputMethodManager is a singleton and three references to DecorView which references HelloWorldActivity.

I can't understand why InputMethodManager still references DecorView instance even after the activity is destroyed.

Is there any way to make sure that the main activity is destroyed and GC-able after closing it?

Answer 1

It seems that calling InputMethodManager's methods 'windowDismissed' and 'startGettingWindowFocus' do the stuff.

Something like this:

@Override
protected void onDestroy()
{
    super.onDestroy();
    //fix for memory leak: http://code.google.com/p/android/issues/detail?id=34731
    fixInputMethodManager();
}

private void fixInputMethodManager()
{
    final Object imm = getSystemService(Context.INPUT_METHOD_SERVICE);

    final Reflector.TypedObject windowToken
        = new Reflector.TypedObject(getWindow().getDecorView().getWindowToken(), IBinder.class);

    Reflector.invokeMethodExceptionSafe(imm, "windowDismissed", windowToken);

    final Reflector.TypedObject view
        = new Reflector.TypedObject(null, View.class);

    Reflector.invokeMethodExceptionSafe(imm, "startGettingWindowFocus", view);
}

Reflector's code:

public static final class TypedObject
{
    private final Object object;
    private final Class type;

    public TypedObject(final Object object, final Class type)
    {
    this.object = object;
    this.type = type;
    }

    Object getObject()
    {
        return object;
    }

    Class getType()
    {
        return type;
    }
}

public static void invokeMethodExceptionSafe(final Object methodOwner, final String method, final TypedObject... arguments)
{
    if (null == methodOwner)
    {
        return;
    }

    try
    {
        final Class<?>[] types = null == arguments ? new Class[0] : new Class[arguments.length];
        final Object[] objects = null == arguments ? new Object[0] : new Object[arguments.length];

        if (null != arguments)
        {
            for (int i = 0, limit = types.length; i < limit; i++)
            {
                types[i] = arguments[i].getType();
                objects[i] = arguments[i].getObject();
            }
        }

        final Method declaredMethod = methodOwner.getClass().getDeclaredMethod(method, types);

        declaredMethod.setAccessible(true);
        declaredMethod.invoke(methodOwner, objects);
    }
    catch (final Throwable ignored)
    {
    }
}