c# - Windows 8 C# 从多个地方访问文件时出现拒绝访问错误

Question

我正在尝试将一些数据保存在一个文件中，但是这个文件被不同的方法多次访问，因此出现访问被拒绝的错误。如何在以下方法上应用锁定来访问文件？

代码:

public static async Task SaveDataToFileAsync<T>(string key, T value, bool roaming = false, Type[] extraTypes = null)
{
    var file = roaming ? await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.ReplaceExisting) :
    await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.ReplaceExisting);

    var xml = Xml.Serialize<T>(value, extraTypes);
    await FileIO.WriteTextAsync(file, xml, UnicodeEncoding.Utf8);
}

public static async Task<T> GetdataFromFileAsync<T>(string key, T defaultValue, bool roaming = false, Type[] extraTypes = null)
{
    var file = roaming ? await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.OpenIfExists) :
    await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.OpenIfExists);

    var xml = await FileIO.ReadTextAsync(file, UnicodeEncoding.Utf8);
    return !String.IsNullOrEmpty(xml) ? Xml.Deserialize<T>(xml, extraTypes) : defaultValue;
}

Answer 1

您可以使用 SemaphoreSlim或 Stephen Toub's AsyncLock . AsyncLock 也可用作 part of我的 AsyncEx 库。

这是一个 AsyncLock 的例子，它的语法比 SemaphoreSlim 更自然:

private static AsyncLock mutex = new AsyncLock();
public static async Task SaveDataToFileAsync<T>(string key, T value, bool roaming = false, Type[] extraTypes = null)
{
  using (await mutex.LockAsync())
  {
    var file = roaming ? await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.ReplaceExisting) :
    await KnownFolders.DocumentsLibrary.CreateFileAsync(key + ".xml", CreationCollisionOption.ReplaceExisting);

    var xml = Xml.Serialize<T>(value, extraTypes);
    await FileIO.WriteTextAsync(file, xml, UnicodeEncoding.Utf8);
  }
}