网络状态判断（3G/WIFI）

//Check network
    public void CheckNetworkState()
    {
        boolean flag = false;
        ConnectivityManager manager = (ConnectivityManager)getSystemService(
                Context.CONNECTIVITY_SERVICE);
        State mobile = manager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState();
        State wifi = manager.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState();
        //如果3G、wifi、2G等网络状态是连接的，则退出，否则显示提示信息进入网络设置界面
        if(mobile == State.CONNECTED||mobile==State.CONNECTING)
        return;
        if(wifi == State.CONNECTED||wifi==State.CONNECTING)
        return;
        showTips();
    }
    
    private void showTips()
    {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setIcon(android.R.drawable.ic_dialog_alert);
        builder.setTitle(R.string.netstate);
        builder.setMessage(R.string.setnetwork);
        builder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
            
            @Override
            public void onClick(DialogInterface dialog, int which) {
                // 如果没有网络连接，则进入网络设置界面
                startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));
            }
        });
        builder.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
            
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        builder.create();
        builder.show();
    }

这种方式更加简单，也更加有用，当然第一篇也有可取之处，可以加入3G状态检查即可
注意：别忘了加上权限

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