Android学习手记(4) BroadcastReceiver监听电池信息

Android 中，Broadcast是一种在应用程序之间进行传输信息的机制。BroadcastReceiver对发送过来的Broadcast进行过滤和响应。根据这种机制，我们可以获取电池现有电量等信息。

1、实例化BroadcastReceiver

在接受信息的时候，可以通过intent.getAction().equals(Intent.ACTION_BATTERY_CHANGED)来判断接收的信息是否为电池电量变化信息。如果是，就获取此信息的详细情况。

 private BroadcastReceiver batteryInfoReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             if(intent.getAction().equals(Intent.ACTION_BATTERY_CHANGED)){
                 int level = intent.getIntExtra("level", 0);
                 int scale = intent.getIntExtra("scale", 100);
                 batteryView.setText("BatteryLevel " + String.valueOf(level*100/scale)+"%");
             }
         }
     };

2、注册消息接收器

在onResume方法内注册消息接收器用来接收消息

registerReceiver(batteryInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

3、注销消息接收器

在onPause方法内注销消息接收器

unregisterReceiver(batteryInfoReceiver);

4、完整代码

 public class MainActivity extends AppCompatActivity {

     private TextView batteryView;
     private BroadcastReceiver batteryInfoReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             if(intent.getAction().equals(Intent.ACTION_BATTERY_CHANGED)){
                 int level = intent.getIntExtra("level", 0);
                 int scale = intent.getIntExtra("scale", 100);
                 batteryView.setText("BatteryLevel " + String.valueOf(level*100/scale)+"%");
             }
         }
     };

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

         batteryView = (TextView) this.findViewById(R.id.batteryView);
     }

     @Override
     protected void onResume(){
         super.onResume();
         registerReceiver(batteryInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
     }

     @Override
     protected void onPause(){
         super.onPause();
         unregisterReceiver(batteryInfoReceiver);
     }
 }

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