在fileStream.CopyTo( memoryStream )之后，memoryStream为空

Question

所以，我有一个函数，它获取BitmapImage，我需要保存到iso存储并转换为Base64 (用于发送到服务器)。但是，从fileStream到memoryStream的复制不会成功。

public void SetImage(BitmapImage bitmap)
{
    if (isoFiles.FileExists(Settings.FILE_AVATAR_JPG))
        isoFiles.DeleteFile(Settings.FILE_AVATAR_JPG);

    var fileStream = isoFiles.CreateFile(Settings.FILE_AVATAR_JPG);
    var wb = new WriteableBitmap(bitmap);
    wb.SaveJpeg(fileStream, 120, 120, 0, 85); // file is saved 

    var memoryStream = new MemoryStream();
    fileStream.CopyTo(memoryStream);          // here, memoryStream is null
    byte[] result = memoryStream.ToArray();
    fileStream.Close();

    var base64 = Convert.ToBase64String(result);
}

Answer 1

Stream.CopyTo从SaveJpeg()修改过的fileStream当前位置复制，需要重新设置；

var memoryStream = new MemoryStream();

fileStream.Position = 0;
fileStream.CopyTo(memoryStream);