判断是否联网

import android.content.Context;import android.content.DialogInterface;import android.content.Intent;import android.net.ConnectivityManager;import android.net.NetworkInfo;import android.provider.Settings;import android.support.v7.app.AlertDialog;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        if(isOnline()){        }else {            //弹出提示对话框            showDialog();        }    }    public boolean isOnline() {        //得到一个连接管理者        ConnectivityManager connMgr = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);        //得到联网信息        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();        //判断设备是否联网        return (networkInfo != null && networkInfo.isConnected());    }    private void showDialog(){        AlertDialog.Builder builder = new AlertDialog.Builder(this);        builder.setMessage("是否联网");        builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {            }        });        builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {                //跳转网络设置界面                startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));            }        });        builder.create().show();    }}