Question

我试图在UWP上使用C＃将BitmapImage存储到文件系统。图像使用图形api从Facebook下载并作为BitmapImage返回。该部分工作，并检索图像（一旦我可以存储它，测试刚刚放在本地文件夹中的图片）我使用以下代码：

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;

这也有效，所以我想要的只是做相反的事情。首选结果如下：

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

}

我试图寻找解决方案，但我似乎找不到任何UWP平台。如何将Bitmap保存到文件？如果更容易使用其他扩展名，则扩展名不必为.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[bmp.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();
    }
}

在LocalFolder中存储BitmapImage - UWP

1 个答案: