Android中使用Handler（消息机制）造成内存泄露的分析和解决

问题描述：

Handler内部类持有外部类Activity的引用，如果Activity退出而Handler还有延迟处理的消息没有处理完，会导致Activuty不能回收，反复如此会导致内存泄漏。

解决方案：

1、onDestory时清除消息

	mHandler.removeCallbacksAndMessages(null); // 参数为null时会清除所有消息。

2、盛行Handler为static并持有Activity的弱引用

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;
            //强调弱引用
            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为空，10s为空-通知Activity被回收
                if (null == activity) {
                    Log.e(tag, "null");
                } else {
                    Log.e(tag, "not null");
                    activity.mTvShow.setText("delay show");
                }
            }
        }
    }