Question

我正在尝试将List（其中Show是我的实现IXmlSerializable的类）存储到本地隔离存储。我正在使用此页面中的代码： http://metrostoragehelper.codeplex.com/ 我已经实现了“问题”部分中建议的更改。我从项目列表中单击时使用以下代码添加Show对象。

private async void addShowButton_Click_1(object sender, RoutedEventArgs e)
    {
        var isoStorage = new StorageHelper<List<Show>>(StorageType.Local);

        List<Show> currentShows = await isoStorage.LoadASync("myShowsEx");
        if(currentShows == null) {
            currentShows = new List<Show>();
        }

        currentShows.Add(currentShow);

        isoStorage.SaveASync(currentShows, "myShowsEx");


        //Read it back, for debugging to check if it has been added properly. 
        List<Show> currentShowsRB = await isoStorage.LoadASync("myShowsEx"); //Exception here

    }

第一个节目添加得很好，它出现在currentShowsRB列表中。单击第二个项目并调用上述方法时，最后一次LoadAsync调用发生异常：拒绝访问。（HRESULT异常：0x80070005（E_ACCESSDENIED））如何解决此问题以访问本地数据存储以进行多次调用？

以下是StorageHelper的相关代码：

public async void SaveASync(T Obj, string FileName)
    {

        FileName = FileName + ".xml";
        try
        {
            if (Obj != null)
            {
                StorageFile file = null;
                StorageFolder folder = GetFolder(storageType);
                file = await folder.CreateFileAsync(FileName, CreationCollisionOption.ReplaceExisting);

                using (var writeStream = await file.OpenAsync(FileAccessMode.ReadWrite))
                {
                    Stream outStream = Task.Run(() => writeStream.AsStreamForWrite()).Result;
                    serializer.Serialize(outStream, Obj);
                    //writeStream.Dispose(); //Added and we get UnauthorizedAccessException
                    // outStream.Dispose(); //Added ObjectDisposedException caught in catch statement below
                }
            }
        }
        catch (Exception)
        {
            throw;
        }
    }
    public async Task<T> LoadASync(string FileName)
    {
        FileName = FileName + ".xml";
        try
        {
            StorageFile file = null;
            StorageFolder folder = GetFolder(storageType);
            file = await folder.GetFileAsync(FileName);
            using (var readStream = await file.OpenAsync(FileAccessMode.Read))
            {
                Stream inStream = Task.Run(() => readStream.AsStreamForRead()).Result;
                inStream.Position = 0;
                return (T)serializer.Deserialize(inStream);
            }
        }
        catch (FileNotFoundException)
        {
            //file not existing is perfectly valid so simply return the default 
            return default(T);
            //throw;
        }
        catch (Exception)
        {
            //Unable to load contents of file
            throw;
        }
    }

我添加了writeStream.Dispose（）行，但即使包含此行，我也会得到相同的Access拒绝错误消息。如果我还包含outStream.Dispose（）行，那么我会在下面的catch语句中捕获一个ObjectDisposedException。还有什么我应该做的吗？

Answer 1

您不是在等待SaveAsync完成，尝试在保存仍在进行时加载。将其更改为：

//isoStorage.SaveASync(currentShows, "myShowsEx");
await isoStorage.SaveASync(currentShows, "myShowsEx");   

List<Show> currentShowsRB = await isoStorage.LoadASync("myShowsEx");

编辑await void是一个标准问题快速解决方法是：

 await TaskEx.Run(() => isoStorage.SaveASync(currentShows, "myShowsEx"));

但您也可以在TaskEx.Run()内移动SaveASync()。如果名称以Async结尾，则不应为void，而是：

Task SaveASyncT Obj, string FileName)
{ 
    return TaskEx.Run() => { .... }
}

我不相信Serialize的异步版本，所以它保持在TaskEx.Run()。

Answer 2

此块可缩短为：

        using (var readStream = await file.OpenAsync(FileAccessMode.Read)) 
        { 
            return (T)serializer.Deserialize(readStream); 
        }

因为您可以直接从XmlSerializer类中的流读取/写入。

您可能还会发现CreationCollisionOption.ReplaceExisting可能会导致问题，OpenIfExists会导致文件被序列化程序覆盖。

在本地存储Windows 8 Metro App中保存对象时拒绝访问

2 个答案: