真正与Activity能交互的回调以及Activity退入后台方法

//监听activity是否有焦点，是否能与用户交互@Override    public void onWindowFocusChanged(boolean hasFocus) {        super.onWindowFocusChanged(hasFocus);        if (hasFocus) {            IntentFilter filter = new IntentFilter();            filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);            filter.addAction(ScanReceiver.SCANNER_ACTION);            registerReceiver(receiver, filter);        } else {            unregisterReceiver(receiver);        }    }

//主要是moveTaskToBack(false);@Override    public void onBackPressed() {        moveTaskToBack(false);    }