Android 广播组件Broadcast Receiver

public class MainActivity extends AppCompatActivity {

    private IntentFilter intentFilter = new IntentFilter();;
    private NetworkChangeReceiver networkChangeReceiver = new NetworkChangeReceiver();

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

        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");

        registerReceiver(networkChangeReceiver,intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
 　　　　//一定要取消
        unregisterReceiver(networkChangeReceiver);
    }

    class NetworkChangeReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
            Toast.makeText(context,"123",Toast.LENGTH_SHORT).show();
        }
    }
}