public class MainActivity extends AppCompatActivity {
    //private ArrayList<String> mList;
    //private MyListAdapter mListAdapter;
    //private ListView mLv;
    private ImagerView iv;
    private Handler mHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case value:
                iv.setImageResoure(...)
                break;
            }
        }
    };
   

 此时就相当于 这个handler是一个内部类, 内部类会持有外部类的引用(iv).
    如果此时activty的被退出了. handler持有他的引用,所有这个activity 并不会被销毁,其实还是在内存中.所有就造成的Context泄漏.

    private Handler mHandler = new MyHandler(this);
    //使用静态的内部类 + 虚引用可以解决这个问题. 
    // 静态的内部类,是随着类的加载而加载,所以静态的内部类就只能访问静态的变量,所以就不就可以解决引用持有问题.
    private static class MyHandler extends Handler{
        private final WeakReference<Activity> mActivity;
        public MyHandler(Activity activity) {
            mActivity = new WeakReference<Activity>(activity);

        }
        @Override
        public void handleMessage(Message msg) {
            System.out.println(msg);
            //这个方法必须做 点get()看注释文档可以知道:
/*Returns this reference object ' s referent .  If this reference object has been cleared , either by the program or by the garbage collector , then this method returns < code > null </ code >.  @ return The object to which this reference refers , or < code > null </ code > if this reference object has been cleared /
 就是通过get()方法可以判断这个对象是否被回收,我们需要判断这个mActivity 是否存在才能做后面的操作..
            */
            if(mActivity.get() == null) {
                return;
            }
        }
    }

还有一种方法就是: