Android中使用Handler造成內存洩露的分析和解決

Handler 內部類持有 外部類Activity的引用，如果Activity退出而Handler還有延遲處理的消息沒有處理完，會導致Activity不能回收，反復如此會導致內存洩露。

解決方案一： onDestroy時清除消息，mHandler.removeCallbacksAndMessages(null); // 參數為null時會清除所有消息。

解決方案二：聲明Handler為static並持有Activity的弱引用。關鍵看程序中注釋的地方

public class MainActivity extends Activity {

    private static final String tag = "MainActivity";

    private TextView mTvShow;

    private MyHandler mHandler;

    private static final int DELAY_TIME = 10000; // set to 5s and 10s to check result.

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

        mHandler = new MyHandler(MainActivity.this);

        Log.e(tag, "onCreate");

        mTvShow = (TextView)findViewById(R.id.tv_show);

        new Thread() {
            @Override
            public void run() {

                mHandler.sendEmptyMessageDelayed(1, DELAY_TIME);
                Log.e(tag, "msg send");
            }
        }.start();

    }

    @Override
    protected void onDestroy() {
        Log.e(tag, "onDestroy");
        super.onDestroy();
    }

    static class MyHandler extends Handler{

        WeakReference mWeakActivity;

        public MyHandler(MainActivity activity) {
            mWeakActivity = new WeakReference<>(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);

            MainActivity activity = mWeakActivity.get();

            Log.e(tag, "handleMessage," + msg.what);
            // 5s is not null, 10s is null, tell that activity is recycled.
            if(null == activity){
                Log.e(tag, "null");
            }else{
                Log.e(tag, "not null");
                activity.mTvShow.setText("delay show");
            }
        }
    }
}