判断是否联网

    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("网络请求失败");

        builder.setNegativeButton("取消",null);

        builder.setPositiveButton("查看网络设置", 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();

    }

重要权限：<</span>uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>