无法隐式转换类型IAsyncOperation< StorageFile>.到StorageFile [英] Cannot implicitly convert type IAsyncOperation<StorageFile> to StorageFile

问题描述

我的代码到底怎么了?

 私有无效的BrowseButton_Click(对象发送者，RoutedEventArgs e){FileOpenPicker FilePicker =新的FileOpenPicker();FilePicker.FileTypeFilter.Add(.exe");FilePicker.ViewMode = PickerViewMode.List;FilePicker.SuggestedStartLocation = PickerLocationId.Desktop;//如果我在这里等我又遇到其他错误¹StorageFile文件= FilePicker.PickSingleFileAsync();如果(文件！= null){AppPath.Text = file.Name;}别的{AppPath.Text =";}} 

它给了我这个错误:

无法将类型"Windows.Foundation.IAsyncOperation"隐式转换为"Windows.Storage.StorageFile"

如果我添加"await"(如在代码中注释)，则会出现以下错误:

¹'await'运算符只能在异步方法中使用.考虑使用'async'修饰符标记此方法，并将其返回类型更改为'Task'.

代码源此处

解决方案

好吧，编译器错误消息非常直接地解释了代码未编译的原因. FileOpenPicker.PickSingleFileAsync 返回 IAsyncOperation< StorageFile> -因此，不能，您不能将该返回值分配给 StorageFile 变量.在C#中使用 IAsyncOperation<> 的典型方法是使用 await .

您只能在 async 方法中使用 await ...因此，您可能希望将方法更改为异步方法:

 私有异步void BrowseButton_Click(对象发送者，RoutedEventArgs e){...StorageFile文件=等待FilePicker.PickSingleFileAsync();...} 

请注意，对于事件处理程序以外的其他任何东西，最好使异步方法返回 Task 而不是 void -使用 void 实际上只是这样，因此您可以使用异步方法作为事件处理程序.

如果您还不太熟悉 async / await ，则应该在继续操作之前先阅读一下-页可能是一个不错的起点.>

What the hell is wrong with my code?

    private void BrowseButton_Click(object sender, RoutedEventArgs e)
    {
        FileOpenPicker FilePicker = new FileOpenPicker();
        FilePicker.FileTypeFilter.Add(".exe");
        FilePicker.ViewMode = PickerViewMode.List;
        FilePicker.SuggestedStartLocation = PickerLocationId.Desktop;
        // IF I PUT AWAIT HERE   V     I GET ANOTHER ERROR¹
        StorageFile file = FilePicker.PickSingleFileAsync();
        if (file != null)
        {
            AppPath.Text = file.Name;
        }
        else
        {
            AppPath.Text = "";
        }         
    }

It gives me this error:

Cannot implicitly convert type 'Windows.Foundation.IAsyncOperation' to 'Windows.Storage.StorageFile'

And if I add the 'await', like commented on the code, I get the following error:

¹ The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'.

Code source here

解决方案

Well, the reason your code doesn't compile is explained pretty directly by the compiler error message. FileOpenPicker.PickSingleFileAsync returns an IAsyncOperation<StorageFile> - so no, you can't assign that return value to a StorageFile variable. The typical way of using IAsyncOperation<> in C# is with await.

You can only use await in async methods... so you probably want to change your method to be asynchronous:

private async void BrowseButton_Click(object sender, RoutedEventArgs e)
{
    ...
    StorageFile file = await FilePicker.PickSingleFileAsync();
    ...
}

Note that for anything other than event handlers, it's better to make an async method return Task rather than void - the ability to use void is really only so you can use an async method as an event handler.

If you're not really familiar with async/await yet, you should probably read up on it before you go any further - the MSDN "Asynchronous Programming with async and await" page is probably a decent starting point.

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