Broadcast 动态注册监听网络变化

这个实验只需要建一个工程，布局文件不需要进行任何修改。

Activity

package com.example.hzx.mybroadcast;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private IntentFilter intentFilter;
    private NetWorkChangeReceiver netWorkChangeReceiver;

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

        //动态注册
        intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        netWorkChangeReceiver = new NetWorkChangeReceiver();
        registerReceiver(netWorkChangeReceiver, intentFilter);

    }

    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(netWorkChangeReceiver);
    }

    class NetWorkChangeReceiver extends BroadcastReceiver {
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isAvailable()){
                Toast.makeText(context, "network is available", Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context, "network is unavailable", Toast.LENGTH_SHORT).show();
            }

        }
    }
}

1、 需要注意在AndroidManifest.xml添加权限
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

效果：
程序隐形后，按下Home健，关闭或者打开WIFI时，会弹出提示。