[Android] Android_监听电池电量

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监听电池变化的方法

Battert Manager会通过一个Intent广播所有电池和充电详情，包含充电状态。Android开发者可以利用BroadcastReceiver机制获取电池电量的变化，通过监听电池电量的变化包含以下几个步骤：

创建一个监听ACTION_BATTERY_CHAGRED事件的 intentFilter
创建一个BroadcastReceiver对象，该对象可以接收broadcase intent
注册BroadcastReceiver对象来监听ACTION_BATTERY_CHANGED事件
在BroadcastReceiver对象中，重写onReceive方法，在onReceive方法的传入参数intent中获取电池的状态
切记的是在生命周期结束时，及时取消BroadcastReceiver的注册，否则出现内存泄漏

具体实现

通常有两种思路，第一种就是自定义一个BroadcastReceiver继承自BroadcastReceiver，并且重写onReceive()方法，在onReceive()方法中根据方法传入的Intent来判断电池的状态，这种方法需要主要的是需要在Manifest文件中注册广播接收器，添加过滤条件；还有一种方法是直接在Activity中定义一个BroadcastReceiver对象并重写onReceive()方法，并且需要定义IntentFilter，同时需要调用registerReceiver方法来将BroadcastReceiver和IntentFilter进行绑定。

这里就第二种方法给出一个例子，代码如下：

package com.glemontree.batterymonitor;import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.BatteryManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;public class MainActivity extends AppCompatActivity {private TextView batteryLevel;private BroadcastReceiver batteryLevelReceiver;private IntentFilter batteryLevelFilter;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);batteryLevel = (TextView) findViewById(R.id.batteryLevel);monitorBatteryState();}@Overrideprotected void onDestroy() {super.onDestroy();unregisterReceiver(batteryLevelReceiver);}private void monitorBatteryState() {batteryLevelReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {StringBuilder sb = new StringBuilder();int rawLevel = intent.getIntExtra("level", -1);int scale = intent.getIntExtra("scale", -1);int status = intent.getIntExtra("status", -1);int health = intent.getIntExtra("health", -1);int level = -1;if (rawLevel >= 0 && scale > 0) {level = (rawLevel * 100) / scale;}sb.append("The phone ");if (BatteryManager.BATTERY_HEALTH_OVERHEAT == health) {sb.append("s battery feels very hot!");} else {switch (status) {case BatteryManager.BATTERY_STATUS_UNKNOWN:sb.append("no battery.");break;case BatteryManager.BATTERY_STATUS_CHARGING:sb.append("s battery");if (level <= 33) {sb.append("is charging, battery level is low" + "[" + level + "]");} else if (level <= 84) {sb.append("is charging." + "[" + level + "]");} else {sb.append("will be fully charged.");}break;case BatteryManager.BATTERY_STATUS_DISCHARGING:case BatteryManager.BATTERY_STATUS_NOT_CHARGING:if (level == 0) {sb.append("needs charging right away.");} else if (level > 0 && level <= 33) {sb.append("is about ready to be recharged, battery level is low"+ "[" + level + "]");} else {sb.append("s battery level is" + "[" + level + "]");}break;case BatteryManager.BATTERY_STATUS_FULL:sb.append("is fully charged.");break;default:sb.append("s battery is indescribable!");break;}}sb.append("");batteryLevel.setText(sb.toString());}};batteryLevelFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);registerReceiver(batteryLevelReceiver, batteryLevelFilter);}
}

代码分析

上面这段代码中，首先在onCreate()方法中定义了一个BroadcastReceiver，并且重写了其onReceive方法，在onReceive()方法中根据传入的Intent，获得电池的一些信息：

int rawLevel = intent.getIntExtra("level", -1);
int scale = intent.getIntExtra("scale", -1);
int status = intent.getIntExtra("status", -1);
int health = intent.getIntExtra("health", -1);

其中，level表示电池的当前剩余电量，scale表示电池的最大值，status表示电池的状态，health则表示电池的健康状态。

在方法的最后定义了IntentFilter用来定义消息过滤，这里过滤的是Intent.ACTION_BATTERY_CHANGED，表示BroadcastReceiver监听电池电量的变化，最后通过registerReceiver方法将BroadcastReceiver和IntentFilter进行绑定。

需要注意的是一定在Activity的onDestroy()方法中调用unRegisterReceiver()方法来取消注册Receiver，当然本例子是在onCreate()方法中调用registerReceiver()来绑定BroadcastReceiver和IntentFilter，你也可以在onResume()方法中进行绑定，甚至于在View中在onAttatchedWindow()方法中进行绑定！