Android的广播机制基础1---动态注册监听的使用，以获得电池的使用状态为例

以一个显示手机电量和电池状态的Demo为例。
1.要获得电池的使用状态，需在AndroidManifest.xml中添加使用权限：

<uses-permission android:name="android.permission.BATTERY_STATS"/>

2.广播有发送方和接收方，接收方为BroadCastReceiver的实例或其子类
3.首先我们写出activity的布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
//电池电量
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/current"
        android:textSize="30sp"/>

    <ProgressBar
        android:layout_width="match_parent"
        android:layout_height="20dp"
        style="@style/Base.Widget.AppCompat.ProgressBar.Horizontal"
        android:id="@+id/progressbar"/>
//电池充电状态
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"
        android:id="@+id/battryeStatus"/>
//电池健康状态
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/batteryHealth"
        android:textSize="30sp"/>

</LinearLayout>

4.activity实现部分

package com.example.apple.broadcast.BatteryMonitor;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.BatteryManager;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.example.apple.broadcast.R;

/**
 * Created by apple on 2018/6/6.
 */

public class BatteryMonitorActivity extends AppCompatActivity {

    private TextView tv_level,tv_status,tv_health;
    private ProgressBar progressbar;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.battry_layout);
//初始化控件
        tv_level=(TextView)findViewById(R.id.current);
        tv_health=(TextView)findViewById(R.id.batteryHealth);
        tv_status=(TextView)findViewById(R.id.battryeStatus);
        progressbar=(ProgressBar)findViewById(R.id.progressbar);
        progressbar.setMax(100);
    }
//注册广播
    @Override
    protected void onResume() {
        super.onResume();
        //IntentFilter传递相应的action
        IntentFilter intentFilter=new IntentFilter();
        intentFilter.addAction(Intent.ACTION_BATTERY_CHANGED);
        //注册传入参数为BroadcastReceiver和Intentfilter的实例
        registerReceiver(mBroadcastReceiver,intentFilter);

    }
//取消广播
    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(mBroadcastReceiver);
    }

//BroadcastReceiver的实例，也可以用BroadcastReceiver的子类实现，书写一个内部类，要重写父类的onReceive方法
    private BroadcastReceiver mBroadcastReceiver=new BroadcastReceiver() {
    //Int 类型值用来判断电池的状态
        int health,level,status;
        @Override
        public void onReceive(Context context, Intent intent) {
        //获取广播的action
            String action=intent.getAction();
            //如果电池电量改变
            if(action==Intent.ACTION_BATTERY_CHANGED){
          level=intent.getIntExtra(BatteryManager.EXTRA_LEVEL,0);

//电池的充电状态，默认为未充电    
            status=intent.getIntExtra(BatteryManager.EXTRA_STATUS,BatteryManager.BATTERY_STATUS_DISCHARGING);

 //获取电池的健康状态
                health=intent.getIntExtra(BatteryManager.EXTRA_HEALTH,BatteryManager.BATTERY_HEALTH_GOOD);
            }

            changeBattry(health,level,status);
        }
    };
//改变布局，将状态变化显示在布局文件中
    private void changeBattry(int health, int level, int status) {
        tv_level.setText("当前电量为："+level+"%");
        progressbar.setProgress(level);
        if(status==BatteryManager.BATTERY_STATUS_CHARGING){
            tv_status.setText("充电状况：正在充电");
        }else if(status==BatteryManager.BATTERY_STATUS_DISCHARGING){
            tv_status.setText("充电状况：未充电");
        }

        if(health==BatteryManager.BATTERY_HEALTH_GOOD){
            tv_health.setText("电池状况：Good");
        }else if(health==BatteryManager.BATTERY_HEALTH_UNKNOWN){
            tv_health.setText("电池状况：unkown");
        }else if(health==BatteryManager.BATTERY_HEALTH_DEAD){
            tv_health.setText("电池状况：Dead");
        }
    }
}