Android学习总结——判断网络状态

package com.example.xch.broadcasttest;

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.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button getNetworkState;
    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getNetworkState=(Button)findViewById(R.id.get_network_state);
        getNetworkState.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.get_network_state:
                intentFilter=new IntentFilter();
                intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");//网络状态发生改变时发出这一条广播
                networkChangeReceiver=new NetworkChangeReceiver();
                registerReceiver(networkChangeReceiver,intentFilter);
                break;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);//关闭广播
    }

    class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            //getSystemService()方法得到ConnectivityManager实例，这是一个系统服务类，用于管理网络连接
            ConnectivityManager connectivityManager= (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            //getActiveNetworkInfo()方法得到NetworkInfo实例
            NetworkInfo networkInfo=connectivityManager.getActiveNetworkInfo();
            //调用NetworkInfo的isAvailable()方法判断当前是否有网络
            if(networkInfo!=null&&networkInfo.isAvailable()){
                Toast.makeText(context,"网络可用",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"网络不可用",Toast.LENGTH_SHORT).show();
            }
        }
    }
}

记得声明权限，否则程序会崩溃。

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