写入文件前如何清除文件

Question

I am using this code to write into my file:

    private async void play_Click(object sender, RoutedEventArgs e)
    {
        String MyScore;

        Double previousScore = 0;

        StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
        var dataFolder1 = await local.CreateFolderAsync("MyFolder", CreationCollisionOption.OpenIfExists);
        var file1 = await dataFolder1.CreateFileAsync("MyFile.txt", CreationCollisionOption.OpenIfExists);
        var file = await dataFolder1.OpenStreamForReadAsync("MyFile.txt");

        using (StreamReader streamReader = new StreamReader(file))
        {

            MyScore = streamReader.ReadToEnd();



        }

        if (MyScore != null && !MyScore.Equals(""))
        {

            previousScore = Convert.ToDouble(MyScore);
        }


        Double CurerentScore = 0;
        Double Total = 0;

        String scoreText = this.ScoreTB.Text;
        CurerentScore = Convert.ToDouble(scoreText);
        Total = previousScore - CurerentScore;


        using (var s = await file1.OpenStreamForWriteAsync())
        {

          byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(Convert.ToString(Total));
            s.Write(fileBytes, 0, fileBytes.Length);

        }
    }

But before writing into it, I want that my file should get cleared. What should I do?

This is what i have tried so far but the problem is that it writes the file up to the filebytes.length and due to that if the new information to be writed in file is less in terms of length in comparison to the privous length then some garbage value or unnecessay thing comes after the end of the new file

Answer 1

You can use this snippet :

StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile file1 = await folder.CreateFileAsync(fileName, 
CreationCollisionOption.ReplaceExisting); // You are going to replace the file
using (Stream s = await file1.OpenStreamForWriteAsync())
{
    byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(Convert.ToString(Total));
    await s.WriteAsync(fileBytes, 0, fileBytes.Length);
}

To quote the documentation :

ReplaceExisting : Create the new file or folder with the desired name, and replaces any file or folder that already exists with that name.

Answer 2

我通过向其中写入一个空字符串来清除文件，然后在文件中写入了我想要的内容。这解决了我的问题，因为文件中没有任何内容，因此我想要写入的所有内容均成功完成。

Answer 3

Simply use Stream.SetLength like this:

using (var s = await file1.OpenStreamForWriteAsync())
{
    // Add this line
    s.SetLength(0);

    // Then write new bytes. use 's.SetLength(fileBytes.Length)' if needed.
    byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(Convert.ToString(Total));
    s.Write(fileBytes, 0, fileBytes.Length);
}