Android：试图产生内存泄漏

Question

I am using the following post to generate a memory leak in a test application

http://android-developers.blogspot.com/2009/01/avoiding-memory-leaks.html

I am using android studio memory profiler and allocation tracker to track the object allocation. I am able to see activity instances created while rotating the screen multiple times. But when I click on "Initiate GC" on android studio all these instances are garbage collected though they hold a static reference to the drawable object. I was expecting these activity objects to be retained and will cause an "Out of memory" exception. Below is the code I have used :

   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       TextView textView = new TextView(this);
        textView.setText("Hello View");
        if(sBackground == null) {
            sBackground = ContextCompat.getDrawable(this,R.drawable.back1mb);
        }
        mTextView = (TextView) findViewById(R.id.txtView);

        textView.setBackgroundDrawable(sBackground);
        setContentView(textView);

    }

Answer 1

The problem is, the blog post you've referenced is very old, and the Android SDK has changed a lot since it was written. In the early days, as the tutorial says:

When a Drawable is attached to a view, the view is set as a callback on the drawable.

However, this isn't true for more recent versions of the Android SDK.

The code for the early version of Drawable.setCallback was (see link ):

public final void setCallback(Callback cb) {
    mCallback = cb;
}

But it now uses a WeakReference (see link ), so won't leak any more:

public final void setCallback(Callback cb) {
     mCallback = new WeakReference<Callback>(cb);
}

You could build against an old version of Android to see the leak behaviour in the blog, or use a different means of creating a leak.