c# - 如何覆盖 UWP 中的文件？

Question

我尝试使用 FileSavePicker 覆盖 UWP 中的当前文件。我提到了这个:https://msdn.microsoft.com/zh-cn/windows/uwp/files/quickstart-reading-and-writing-files但是当我用一个较短的文件覆盖一个较长的文件时，出现了一个问题:旧文件(较长)的额外部分没有被删除，就像这样:

旧文件:

abcdefg

以及我要保存的文件:

hij

但是在保存操作之后，我得到了这个:

hijdefg

我的代码在这里:

        private async void Save_Click(object sender, RoutedEventArgs e)
    {
        XmlDocument Line = SaveToXml();

        //Save it
        FileSavePicker fileSaving = new FileSavePicker();
        fileSaving.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
        fileSaving.SuggestedFileName = "NewLine";
        fileSaving.FileTypeChoices.Add("Simple Line Files", new List<string>() { ".Line" });
        StorageFile file = await fileSaving.PickSaveFileAsync();

        if (file != null)
        {
            CachedFileManager.DeferUpdates(file);
            var stream = await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
            //var stream = await file.OpenStreamForWriteAsync();
            using (var outputStream = stream.GetOutputStreamAt(0))
            {
                using (var dataWriter = new Windows.Storage.Streams.DataWriter(outputStream))
                {
                    string xmlDoc = Line.OuterXml;
                    Debug.WriteLine(Line.OuterXml);
                    dataWriter.WriteString(xmlDoc);
                    await dataWriter.StoreAsync();
                    await outputStream.FlushAsync();
                }
            }
            stream.Dispose();
        }
    }

谢谢你帮助我!

Answer 1

您也可以在打开流后立即调用 Stream.SetLength(0) 以在开始写入之前清除它。

var streamToWrite = await file.OpenStreamForWriteAsync().ConfigureAwait(false);
streamToWrite.SetLength(0);
using (var streamWriter = new StreamWriter(streamToWrite))
{
    streamWriter.Write(data);
    streamWriter.Flush();                        
}