c# - 如何关闭打开的StorageFile？

Question

我正在编写一个Windows Phone 8.1 (WINRT XAML) 应用。

在方法 1 中，我打开一个 StorageFile，在方法 2 中，我在同一个文件上写入。但是它在写入文件时显示错误。

1. 如何在打开并阅读内容后关闭此文件？

2. 那么方法2写入后如何再次关闭这个文件呢？

   private async Task<bool> Method1(int workOutID)
   {
       string filename = "WorkoutOfflineDataFile.txt";
       StorageFolder LocalStorageFolderObject = ApplicationData.Current.LocalFolder;
       StorageFile StorageFileObject = await LocalStorageFolderObject.CreateFileAsync(filename, CreationCollisionOption.OpenIfExists);
       string JSONFromFile = await FileIO.ReadTextAsync(StorageFileObject);
   }
   
   private async void Method2()
   {
       string filename = "WorkoutOfflineDataFile.txt";
       StorageFolder LocalStorageFolderObject = ApplicationData.Current.LocalFolder;
       StorageFile StorageFileObject = await LocalStorageFolderObject.CreateFileAsync(filename, CreationCollisionOption.OpenIfExists);
       await FileIO.WriteTextAsync(StorageFileObject, JSonData_ToSave);
   }
   

ERROR:

Exception thrown: 'System.UnauthorizedAccessException' in mscorlib.ni.dll

Additional information: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

Answer 1

代码似乎是正确的，我认为异常是由其他东西抛出的。

无论如何，如果你想确保你的文件和流在读/写操作后关闭，你可以使用一次性方式:

private async Task<bool> Method1(int workOutID)
{
    string filename = "WorkoutOfflineDataFile.txt";
    StorageFolder LocalStorageFolderObject = ApplicationData.Current.LocalFolder;
    StorageFile StorageFileObject = await LocalStorageFolderObject.CreateFileAsync(filename, CreationCollisionOption.OpenIfExists);
    using (var stream = await StorageFileObject.OpenStreamForReadAsync())
    {
        using (var reader = new StreamReader(stream))
        {
            string JSONFromFile = reader.ReadToEnd();
        }
    }
}

private async void Method2()
{
    string filename = "WorkoutOfflineDataFile.txt";
    StorageFolder LocalStorageFolderObject = ApplicationData.Current.LocalFolder;
    StorageFile StorageFileObject = await LocalStorageFolderObject.CreateFileAsync(filename, CreationCollisionOption.OpenIfExists);
    using (var stream = await StorageFileObject.OpenStreamForWriteAsync())
    {
        using (var writer = new StreamWriter(stream))
        {
            writer.Write(JSonData_ToSave);
        }
    }
}