附加到文本文件（不覆盖！）

Question

我还问的另一个通用平台应用程序问题，还在学习中！

快速问题-我需要使用哪种方法将数据写入文本文件以将字符串追加（而不是覆盖）文本文件？目前，我正在使用异步异步流，但它正在覆盖我的文件。以下是创建和写入文本文件的不同方法：https : //msdn.microsoft.com/zh-cn/library/windows/apps/mt185401.aspx

目前，这是我的代码。是否需要修改以将数据附加到文本文件而不是覆盖它，还是需要使用其他方法之一来附加数据？

//WRITE
        //Create the text file to hold the data
        Windows.Storage.StorageFolder storageFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
        Windows.Storage.StorageFile ticketsFile = await storageFolder.CreateFileAsync("tickets.txt", Windows.Storage.CreationCollisionOption.OpenIfExists);

        //Use stream to write to the file
        var stream = await ticketsFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);

        using (var outputStream = stream.GetOutputStreamAt(0))
        {
            using (var dataWriter = new Windows.Storage.Streams.DataWriter(outputStream))
            {
                dataWriter.WriteString("Submitted: " + submitDate + "\n" + "Problem: " + problem + "\n" + "Room: " + location + "\n" + "Description: " + descriptionText.Text + "\n" + "Priority: " + priority + "\n");
                await dataWriter.StoreAsync();
                await outputStream.FlushAsync();
            }
        }
        stream.Dispose(); // Or use the stream variable (see previous code snippet) with a using statement as well.

如果有什么不同，请阅读我的代码：

//READ
        //Open the text file
        stream = await ticketsFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
        ulong size = stream.Size;

        using (var inputStream = stream.GetInputStreamAt(0))
        {
            using (var dataReader = new Windows.Storage.Streams.DataReader(inputStream))
            {
                uint numBytesLoaded = await dataReader.LoadAsync((uint)size);
                string savedTickets = dataReader.ReadString(numBytesLoaded);

                textBox.Text = savedTickets;
            }
        }

谢谢。

Answer 1

我现在没有可以测试的平台，但这应该可以获取现有文件的长度并将编写器放在末尾（新文件应返回0）：

using (var outputStream = stream.GetOutputStreamAt(stream.Size))

Answer 2

除了获取流之外，还可以使用FileIO类。例如方法AppendTextAsync：

await FileIO.AppendTextAsync(ticketsFile, "Submitted: " + submitDate + "\n" + "Problem: " + problem + "\n" + "Room: " + location + "\n" + "Description: " + descriptionText.Text + "\n" + "Priority: " + priority + "\n");