判段是否联网

 //判断是否有网
         if (isOnline()){
             btn.setOnClickListener(new View.OnClickListener() {
                 @Override
                 public void onClick(View v) {
                     get();
                 }
             });
         }else {
            nowang();
        }

        return view;
    }
    public boolean isOnline() {
        //得到网络连接的管理者                                这里是Fragment的情况，没有用Fragment就把getactivity（）去掉
        ConnectivityManager connMgr = (ConnectivityManager)getActivity().getSystemService(Context.CONNECTIVITY_SERVICE);
        //通过网络管理者得到网络信息
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        //判断网络是否连接
        return (networkInfo != null && networkInfo.isConnected());
    }
    public void nowang(){
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setMessage("要么去死，要么开网!");
        builder.setNegativeButton("你敢不开网",null);
        builder.setPositiveButton("开网才好孩子", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //设置跳转网络界面
                startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));
            }
        });

        builder.create().show();
    }