C# 将FileSavePicker更改为从独立存储而不是应用存储保存文件。例外情况WP8.1

用var…行更新了SoundData中的代码。实际上，我已经看到了要保存到现在的文件夹，但是当我尝试选择一个文件夹并保存到它时，我遇到了一个异常

+$exception{System.IO.FileNotFoundException:系统找不到指定的文件。

在app.xaml.cs上：

private async void Application_ContractActivated(object sender, Windows.ApplicationModel.Activation.IActivatedEventArgs e)
    {
        var args = e as FileSavePickerContinuationEventArgs;
        if (args != null)
        {
            StorageFile file = args.File;
            if (file != null)
            {
                // Prevent updates to the remote version of the file until we finish making changes and call CompleteUpdatesAsync. 
                CachedFileManager.DeferUpdates(file);
                // write to file 
                var sourceFilePath = args.ContinuationData["SourceSound"].ToString();  
                StorageFolder folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
                StorageFile sourceFile = await folder.GetFileAsync(sourceFilePath);

                IRandomAccessStreamWithContentType sourceStream = await sourceFile.OpenReadAsync();

             var bytes = new byte[sourceStream.Size];

             var sourceBuffer = await sourceStream.ReadAsync(bytes.AsBuffer(), (uint)sourceStream.Size, Windows.Storage.Streams.InputStreamOptions.None);

                await FileIO.WriteBufferAsync(file, sourceBuffer);
                // Let Windows know that we're finished changing the file so the other app can update the remote version of the file. 
                // Completing updates may require Windows to ask for user input. 
                FileUpdateStatus status = await CachedFileManager.CompleteUpdatesAsync(file);
            }
        }
    }

IStorageFile sourceFile=wait folder.GetFileAsync（sourceFilePath）；

App.xaml.cs：

private async void Application_ContractActivated(object sender, Windows.ApplicationModel.Activation.IActivatedEventArgs e)
    {
        var args = e as FileSavePickerContinuationEventArgs;
        if (args != null)
        {
            StorageFile file = args.File;
            if (file != null)
            {
                // Prevent updates to the remote version of the file until we finish making changes and call CompleteUpdatesAsync. 
                CachedFileManager.DeferUpdates(file);
                // write to file 
                var sourceFilePath = args.ContinuationData["SourceSound"].ToString();  
                StorageFolder folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
                StorageFile sourceFile = await folder.GetFileAsync(sourceFilePath);

                IRandomAccessStreamWithContentType sourceStream = await sourceFile.OpenReadAsync();

             var bytes = new byte[sourceStream.Size];

             var sourceBuffer = await sourceStream.ReadAsync(bytes.AsBuffer(), (uint)sourceStream.Size, Windows.Storage.Streams.InputStreamOptions.None);

                await FileIO.WriteBufferAsync(file, sourceBuffer);
                // Let Windows know that we're finished changing the file so the other app can update the remote version of the file. 
                // Completing updates may require Windows to ask for user input. 
                FileUpdateStatus status = await CachedFileManager.CompleteUpdatesAsync(file);
            }
        }
    }

SoundData视图模型：

 private async void ExecuteSaveSoundAs(string soundPath)
    {

        var file = await ApplicationData.Current.LocalFolder.GetFileAsync(SavePath);

        FileSavePicker savePicker = new FileSavePicker();
        savePicker.SuggestedSaveFile = file;
        savePicker.FileTypeChoices.Add("MP3", new List<string>() { ".mp3" });
        savePicker.ContinuationData.Add("SourceSound", SavePath);
        savePicker.SuggestedFileName = this.Title;
        savePicker.PickSaveFileAndContinue();
    }


    public SoundData()
    {
        SaveSoundAs = new RelayCommand<string>(ExecuteSaveSoundAs);            
    }

以下是解决方案：

Mainpage.cs中的代码已修改：

 var sourceFilePath = args.ContinuationData["SourceSound"].ToString();
                StorageFolder folder = ApplicationData.Current.LocalFolder;
                StorageFile sourceFile = await folder.GetFileAsync(sourceFilePath);

以及我的FileSavePicker代码：

private async void ExecuteSaveSoundAs(string soundPath)
    {

        var file = await ApplicationData.Current.LocalFolder.GetFileAsync(SavePath);

        FileSavePicker savePicker = new FileSavePicker();
        savePicker.SuggestedSaveFile = file;
        savePicker.FileTypeChoices.Add("MP3", new List<string>() { ".mp3" });
        savePicker.ContinuationData.Add("SourceSound", SavePath);
        savePicker.SuggestedFileName = this.Title;
        savePicker.PickSaveFileAndContinue();
    }

private async void ExecuteSaveSoundAs（字符串声音路径）
{
var file=wait ApplicationData.Current.LocalFolder.GetFileAsync（保存路径）；
FileSavePicker savePicker=新FileSavePicker（）；
savePicker.SuggestedSaveFile=文件；
savePicker.FileTypeChoices.Add（“MP3”，newlist（）{.MP3}）；
savePicker.ContinuationData.Add（“SourceSound”，SavePath）；
savePicker.SuggestedFileName=this.Title；
savePicker.PickSaveFileAndContinue（）；
}