取得手机电池的剩余量

/*
 * 取得手机电池的剩余量
 * Android API中的BroadcastReceiver(Android.content.BroadcastReceiver)
 * 类有点像Button中的Listener，当Receiver被注册后，会在后台等待其他程序
 * 的调用，程序将通过注册BroadcastReceiver时设置的IntentFilter来捕捉系统
 * 发出的Intent.ACTION_BATTERY_CHANGED这个action,再以此取得手机电池的剩
 * 余量。
 */

import 略;

public class Ex06_02Activity extends Activity {
	private int intLevel;
	private int intScale;
	private Button mButton01;
	private AlertDialog d;
	// 创建BroadcastReceiver
	private BroadcastReceiver mBatInfoReveiver = new BroadcastReceiver() {

		@Override
		public void onReceive(Context context, Intent intent) {
			// TODO Auto-generated method stub
			String action = intent.getAction();
			// 如果捕捉到action是ACRION_BATTERY_CHANGED
			// 就运行onBatteryInfoReveiver()
			if (intent.ACTION_BATTERY_CHANGED.equals(action)) {
				intLevel = intent.getIntExtra("level", 0);
				intScale = intent.getIntExtra("scale", 100);
				onBatteryInfoReceiver(intLevel, intScale);
			}
		}
	};

	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		mButton01 = (Button) findViewById(R.id.myButton1);
		mButton01.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				// 注册一个BroadcastReceiver，作为访问电池计量之用
				registerReceiver(mBatInfoReveiver, new IntentFilter(
						Intent.ACTION_BATTERY_CHANGED));
			}
		});
	}

	// 拦截到ACTION_BATTRY_CHANGED后要执行的动作
	private void onBatteryInfoReceiver(int intLevel, int intScale) {
		// TODO Auto-generated method stub
		d = new AlertDialog.Builder(Ex06_02Activity.this).create();
		d.setTitle(R.string.str_dialog_title);
		d.setMessage(getResources().getString(R.string.str_dialog_body)
				+ String.valueOf(intLevel * 100 / intScale) + "%");
		d.setButton(getResources().getString(R.string.str_button2),
				new DialogInterface.OnClickListener() {

					@Override
					public void onClick(DialogInterface dialog, int which) {
						// TODO Auto-generated method stub
						// 取消注册，并关闭对话框
						unregisterReceiver(mBatInfoReveiver);
						d.dismiss();
					}
				});
		d.show();
	};
}

下面我们来看看程序运行后的结果：

在Android API中有提到，要注册Intent.ACTION_BATTERY_CHANGED的Receiver只能在程序中以
Context.register Receiver()方法来注册，而不能直接在AndroidManifest.xml中注册。