Android Handler改变了WeakReference

Question

我的静态处理程序有一个WeakReference对我Activity(这是为了防止记录良好的内存泄漏问题).

我发布了一条很长的延迟消息,我希望这条消息传递给我的活动(应该在前台).

我担心的是,在方向改变时,我的活动被破坏,处理程序引用了应该被销毁的旧活动.

为了在我onCreate的活动中解决这个问题,我这样做了.

    if(mHandler == null)
        mHandler = new LoginHandler(this);
    else {
        mHandler.setTarget(this);
    }

我的处理程序被声明为一个静态全局变量:

private static LoginHandler     mHandler            = null;

并且实现类也是静态的,如下所示:

private static class LoginHandler extends Handler {

    private WeakReference<LoginActivity>    mTarget;

    LoginHandler(LoginActivity target) {
        mTarget = new WeakReference<LoginActivity>(target);
    }

    public void setTarget(LoginActivity target) {
        mTarget = new WeakReference<LoginActivity>(target);
    }

    @Override
    public void handleMessage(Message msg) {
        // process incoming messages here
        LoginActivity activity = mTarget.get();
        switch (msg.what) {
            case Constants.SUCCESS:
                activity.doSomething();
                break;

            default:
                activity.setStatusMessage("failed " + msg.obj, STATUS_TYPE_DONE);
        }
    }
}

我想知道的是,更改WeakReference onCreate是否有问题,或者这种方法还有什么问题吗？

谢谢,

Answer 1

所以我写了下面的测试,以确定我是否有正确的想法,似乎m方法是正确的.在onCreate我们更改时WeakReference,发布的消息将始终传递到前台的活动.如果您更改此代码以始终创建新的处理程序,onCreate您会注意到更新消息无法传递.

public class MainActivity extends Activity {

    private static int COUNT = 0;

    static LoginHandler mHandler;

    private static class LoginHandler extends Handler {

        private WeakReference<MainActivity> mTarget;

        LoginHandler(MainActivity target) {
            mTarget = new WeakReference<MainActivity>(target);
        }

        public void setTarget(MainActivity target) {
            mTarget.clear();
            mTarget = new WeakReference<MainActivity>(target);
        }

        @Override
        public void handleMessage(Message msg) {
            // int duration = Toast.LENGTH_LONG;
            // process incoming messages here
            MainActivity activity = mTarget.get();
            activity.update(msg.arg1);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(mHandler == null)
            mHandler = new LoginHandler(this);
        else
            mHandler.setTarget(this);

        ((Button)findViewById(R.id.button)).setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Message msg = new Message();
                msg.arg1 = COUNT++;
                mHandler.sendMessageDelayed(msg, 3000);

            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private void update(int count) {
        ((TextView) findViewById(R.id.hello_world)).setText("Hello World @ "+ count);
    }

}