c# - 在 LocalFolder 中存储 BitmapImage - UWP

Question

我正在尝试在 UWP 上使用 C# 将 BitmapImage 存储到文件系统。该图像是使用图形 API 从 Facebook 下载的，并作为 BitmapImage 返回。那部分工作，并检索图像(一旦我可以存储它，用刚刚放在本地文件夹中的图片进行测试)我正在使用以下代码:

public static async Task<BitmapImage> GetProfilePicture(string userId){
    BitmapImage profilePicture = new BitmapImage(); 

    StorageFolder pictureFolder = await
                  ApplicationData.Current.LocalFolder.GetFolderAsync("ProfilePictures");
    StorageFile pictureFile = await pictureFolder.GetFileAsync(userId + ".jpg");
    IRandomAccessStream stream = await pictureFile.OpenAsync(FileAccessMode.Read);
    profilePicture.SetSource(stream);

    return profilePicture;   

这也行得通，所以我只想做相反的事情。首选结果如下所示:

public static async void SaveBitmapToFile(BitmapImage  image, userId){
    StorageFolder pictureFolder = await
        ApplicationData.Current.LocalFolder.CreateFolderAsync(
            "ProfilePictures",CreationCollisionOption.OpenIfExists);

       //save bitmap to pictureFolder with name userId.jpg

}

我进行了广泛的搜索，试图找到解决方案，但我似乎找不到适用于 UWP 平台的任何解决方案。如何将位图保存到文件？如果使用其他扩展名会更容易，则扩展名不必是 .jpg。

Answer 1

如果使用 WriteableBitmap 会更容易。例如，第一种方法是:

public static async Task<WriteableBitmap> GetProfilePictureAsync(string userId)
{
    StorageFolder pictureFolder = await ApplicationData.Current.LocalFolder.GetFolderAsync("ProfilePictures");
    StorageFile pictureFile = await pictureFolder.GetFileAsync(userId + ".jpg");

    using (IRandomAccessStream stream = await pictureFile .OpenAsync(FileAccessMode.Read))
    {
        BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
        WriteableBitmap bmp = new WriteableBitmap((int)decoder.PixelWidth, (int)decoder.PixelHeight);

        await bmp.SetSourceAsync(stream);

        return bmp;
    }
}

然后你可以这样做:

public static async Task SaveBitmapToFileAsync(WriteableBitmap image, userId)
{
    StorageFolder pictureFolder = await ApplicationData.Current.LocalFolder.CreateFolderAsync("ProfilePictures",CreationCollisionOption.OpenIfExists);
    var file = await pictureFolder.CreateFileAsync(userId + ".jpg", CreationCollisionOption.ReplaceExisting);

    using (var stream = await file.OpenStreamForWriteAsync())
    {
        BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream.AsRandomAccessStream());
        var pixelStream = image.PixelBuffer.AsStream();
        byte[] pixels = new byte[image.PixelBuffer.Length];

        await pixelStream.ReadAsync(pixels, 0, pixels.Length);

        encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, (uint)image.PixelWidth, (uint)image.PixelHeight, 96, 96, pixels);

        await encoder.FlushAsync();
    }
}