c# - 无法将 IStorageItem 转换为 StorageFile

Question

以下代码将无法编译，因为 IsOfType 不被接受为项目的方法。文档指出:

When this method completes successfully, it returns an IStorageItem that represents the specified file or folder. If the specified file or folder is not found, this method returns null instead of raising an exception.

To work with the returned item, call the IsOfType method of the IStorageItem interface to determine whether the item is a file or a folder. Then cast the item to a StorageFolder or StorageFile.

private async void RestoreData(string fileName)
    {
        StorageFolder folder = ApplicationData.Current.LocalFolder;
        var item = folder.TryGetItemAsync(fileName);
        if (item == null)
        {
            existingData = false;
        }
        if (item.IsOfType(StorageItemTypes.File))
        {
            await ReadDataAsync(item as StorageFile);
            existingData = true;
        }
        existingData = false;
    }

Answer 1

你错过了await等待异步方法结果的关键字 - 在这种情况下，您应该这样写:

var item = await folder.TryGetItemAsync(fileName);

多亏了item类型为 IStorageItem而在您的代码中，它的类型是 IAsyncOperation<IStorageItem> .

通过 convention , 所有异步方法都有 Async后缀，你需要等待结果来检查它。

提示:

在大多数 IDE 中，当您将鼠标悬停在 var 上时关键字，将显示一种类型的变量 - 这使得查找错误变得更加容易。