android中的handler定时任务

 private class Scanner extends Handler {
        private int mRetry = 0;

        void resume() {
            if (!hasMessages(0)) {
                sendEmptyMessage(0);
            }
        }

        void forceScan() {
            removeMessages(0);
            sendEmptyMessage(0);
        }

        void pause() {
            mRetry = 0;
            removeMessages(0);
        }

        @Override
        public void handleMessage(Message message) {
            if (mWifiManager.startScanActive()) {
                mRetry = 0;
            } else if (++mRetry >= 3) {
                mRetry = 0;
                Toast.makeText(getActivity(), R.string.wifi_fail_to_scan,
                        Toast.LENGTH_LONG).show();
                return;
            }
            sendEmptyMessageDelayed(0, WIFI_RESCAN_INTERVAL_MS);
        }
    }