问题

我有一个Dart类，其中有一个用于显示警报的辅助方法。该警报在应用程序中多次显示，但是在不同位置上的警报上的onPressed()执行不同的操作。我想将我希望onPressed()执行的操作作为参数传递。

这是我的辅助方法：

basicAlertWithOkWithCallback(String message, BuildContext context, void Function() f){
    
  showDialog(
    context: context,
    builder: (context) =>
        AlertDialog(
          content: Text(message),
          actions: <Widget>[
            TextButton(
              child: const Text('OK'),
              onPressed: () async {
                f();
              },
            ),
          ],
        ),
  );
}

我从另一个屏幕这样调用该方法：

basicAlertWithOkWithCallback('Session successfully saved.', context, callBack(context));

并且在该屏幕上，我创建了以下方法，当按下OK按钮时我希望执行它：

callBack(BuildContext context){
  print('CALLED');
  Navigator.of(context).pop();
  Navigator.of(context).pop();
  Navigator.of(context).pop();
}

问题是，这个方法在警报显示后立即被调用，甚至在用户按下OK按钮之前就被调用。为什么会立即调用，而不是在onPressed()中调用？

basicAlertWithOkWithCallback(String message, BuildContext context, void Function() f){

  showDialog(
    context: context,
    builder: (context) =>
        AlertDialog(
          content: Text(message),
          actions: <Widget>[
            TextButton(
              child: const Text('OK'),
              onPressed: () async {
                f;
              },
            ),
          ],
        ),
  );
}

callBack(BuildContext context){
  print('CALLED');
  Navigator.of(context).pop();
  Navigator.of(context).pop();
  Navigator.of(context).pop();
}

答案1

得分: 2

callBack方法在调用basicAlertWithOkWithCallback时立即被调用的原因是因为你在调用basicAlertWithOkWithCallback方法时调用了callBack方法并将其返回值作为参数传递给basicAlertWithOkWithCallback方法，而不是直接传递callBack方法本身。

要解决这个问题，你需要像这样将callBack方法作为参数传递给basicAlertWithOkWithCallback方法：

basicAlertWithOkWithCallback('Session successfully saved.', context, callBack);

请注意，在上述代码中我们没有使用()调用callBack方法。相反，我们传递了对callBack方法的引用，以便在用户按下'OK'按钮时稍后调用它。

此外，你需要通过在onPressed回调的f参数后添加()来调用onPressed回调中的f函数，像这样：

onPressed: () async 
{
  f();
},
通过这样做，callBack方法只会在用户按下'OK'按钮时调用。

<details>
<summary>英文:</summary>

The reason why callBack method is called immediately when basicAlertWithOkWithCallback is called is because you are invoking the callBack method and passing its return value as a parameter to basicAlertWithOkWithCallback method, instead of passing the callBack method itself.

To fix this, you need to pass the callBack method as a parameter to basicAlertWithOkWithCallback method like this:

    basicAlertWithOkWithCallback(&#39;Session successfully saved.&#39;, context, callBack);

Notice that we are not invoking the callBack method with () in the above code. Instead, we are passing a reference to the callBack method, so that it can be invoked later when the user presses the &#39;OK&#39; button.

Also, you need to invoke the f function inside the onPressed callback by adding () after the f parameter like this:

    onPressed: () async 
    {
      f();
    },
By doing this, the callBack method will only be called when the user presses the &#39;OK&#39; button.


</details>



# 答案2
**得分**: 0

```dart
class SomeWidget extends StatelessWidget {
  const SomeWidget({Key? key, required this.ontap}) : super(key: key);

  final VoidCallback ontap;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: ontap,
      child: Container(),
    );
  }
}


// call it like this
SomeWidget(ontap: (){})

class SomeWidget extends StatelessWidget {
  const SomeWidget({Key? key, required this.ontap}) : super(key: key);

  final VoidCallback ontap;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: ontap,
      child: Container(),
    );
  }
}


// call it like this
SomeWidget(ontap: (){})