c# – 无法将IAsyncOperation类型隐式转换为StorageFile

我的代码到底有什么问题？

    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 = "";
        }         
    }

它给了我这个错误：

Cannot implicitly convert type ‘Windows.Foundation.IAsyncOperation’ to ‘Windows.Storage.StorageFile’

如果我添加’await’,就像在代码上发表评论一样,我收到以下错误：

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’.

代码源here

解决方法:

好吧,编译错误消息直接解释了代码无法编译的原因. FileOpenPicker.PickSingleFileAsync返回IAsyncOperation< StorageFile> – 所以不,您不能将该返回值分配给StorageFile变量.使用IAsyncOperation<>的典型方法在C#等待.

您只能在异步方法中使用await …因此您可能希望将方法更改为异步：

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

请注意,除了事件处理程序之外的任何其他内容,最好使异步方法返回Task而不是void – 使用void的能力实际上只是因为您可以使用异步方法作为事件处理程序.

如果你还不熟悉async / await,你应该在进一步阅读之前阅读它 – MSDN “Asynchronous Programming with async and await”页面可能是一个不错的起点.

标签：c,async-await,microsoft-metro,filepicker,storagefile
来源： https://codeday.me/bug/20190620/1244076.html