Android 如何监听网络变化

一、如何新建一个简单的广播接收器
（1）注册广播的形式分为动态注册（代码中注册）和静态注册（AndroidMainfest.xml中注册）；
（2）新建一个广播接收器来接收广播，广播接收器有一个父类需要继承BroadcastReceiver；

//Intent过滤器
private IntentFilter intentFilter;
//网络变化广播接收器
private NetWorkChangeReceiver netWorkChangeReceiver;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
intentFilter = new IntentFilter();
//添加需要过滤的Action到IntentFilter
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
netWorkChangeReceiver = new NetWorkChangeReceiver();
//注册广播接收器
registerReceiver(netWorkChangeReceiver, intentFilter);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}

class NetWorkChangeReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
//如果网络变化，输出network changes
Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
}
}

@Override
protected void onDestroy() {
super.onDestroy();
//取消注册
unregisterReceiver(netWorkChangeReceiver);
}

二、运行效果图