如何在 Windows Phone 8 上使用 Windows.Storage 正确读取和写入文件

Question

我只需要在 Windows Phone 8 中使用 Windows.Storage API 简单地写入文件和读取文件。使用旧的 IsolatedStorage 方法相对容易，但使用新的 WinRT API 则要困难得多。

我一直在尝试写它，但似乎有所有这些奇怪的东西，比如 IBuffer。等等。使用完整版的 WinRT，使用似乎存在的 Windows.Storage.FileIO 非常容易，以防止像我这样的开发人员发疯。但是，它没有在电话版本中实现。另外，我观看了一个 Channel9 视频，其中显示了一些代码示例，但他们犯了一个错误，因为他们使用了标记为 Security Critical 的方法来获取常规流。显然，不允许获得常规流。

那么，有人可以为我提供一个简洁且正确的 sn-p，说明如何将文件读入字符串以及如何将字符串写入文件，以及正确的使用和处理技术吗？

Answer 1

我没有在 Windows Phone 8 上尝试过，但here's WinRT XAML Toolkit 为 Windows 8 提供的东西可以工作。



using System;
using System.Threading.Tasks;
using Windows.Storage;
using Windows.Storage.Streams;

namespace WinRTXamlToolkit.IO.Extensions
{
    /// <summary>
    /// Extensions for simple writing and reading of strings to/from files.
    /// </summary>
    /// <remarks>
    /// Note that these were created before FileIO class existed in WinRT, but they still serve a purpose.
    /// </remarks>
    public static class StringIOExtensions
    {
        /// <summary>
        /// Reads a string from a text file.
        /// </summary>
        /// <param name="fileName">Name of the file.</param>
        /// <param name="folder">The folder.</param>
        /// <returns></returns>
        public static async Task<string> ReadFromFile(
            string fileName,
            StorageFolder folder = null)
        {
            folder = folder ?? ApplicationData.Current.LocalFolder;
            var file = await folder.GetFileAsync(fileName);

            using (var fs = await file.OpenAsync(FileAccessMode.Read))
            {
                using (var inStream = fs.GetInputStreamAt(0))
                {
                    using (var reader = new DataReader(inStream))
                    {
                        await reader.LoadAsync((uint)fs.Size);
                        string data = reader.ReadString((uint)fs.Size);
                        reader.DetachStream();

                        return data;
                    }
                }
            }
        }

        /// <summary>
        /// Writes a string to a text file.
        /// </summary>
        /// <param name="text">The text to write.</param>
        /// <param name="fileName">Name of the file.</param>
        /// <param name="folder">The folder.</param>
        /// <param name="options">
        /// The enum value that determines how responds if the fileName is the same
        /// as the name of an existing file in the current folder. Defaults to ReplaceExisting.
        /// </param>
        /// <returns></returns>
        public static async Task WriteToFile(
            this string text,
            string fileName,
            StorageFolder folder = null,
            CreationCollisionOption options = CreationCollisionOption.ReplaceExisting)
        {
            folder = folder ?? ApplicationData.Current.LocalFolder;
            var file = await folder.CreateFileAsync(
                fileName,
                options);
            using (var fs = await file.OpenAsync(FileAccessMode.ReadWrite))
            {
                using (var outStream = fs.GetOutputStreamAt(0))
                {
                    using (var dataWriter = new DataWriter(outStream))
                    {
                        if (text != null)
                            dataWriter.WriteString(text);

                        await dataWriter.StoreAsync();
                        dataWriter.DetachStream();
                    }

                    await outStream.FlushAsync();
                }
            }
        }
    }
}

Answer 2

这是一个简单的例子：

public async Task WriteDataToFileAsync(string fileName, string content)
{
    byte[] data = Encoding.Unicode.GetBytes(content);

    var folder = ApplicationData.Current.LocalFolder;
    var file = await folder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

    using (var s = await file.OpenStreamForWriteAsync())
    {
        await s.WriteAsync(data, 0, data.Length);
    }
}

public async Task<string> ReadFileContentsAsync(string fileName)
{
    var folder = ApplicationData.Current.LocalFolder;

    try
    {
        var file = await folder.OpenStreamForReadAsync(fileName);

        using (var streamReader = new StreamReader(file))
        {
            return streamReader.ReadToEnd();
        }
    }
    catch (Exception)
    {
        return string.Empty;
    }
}

像这样使用它们：

await this.WriteDataToFileAsync("afile.txt", "some text to save in a file");

var contents = await this.ReadFileContentsAsync("afile.txt");