Question

我正在尝试以编程方式保存在Windows Phone 8.1（C＃）应用程序中的JPG / PNG / BMP图像中创建的UIElement。

我使用RenderAsync（）方法使用RenderTargetBitmap类，但它只适用于在XAML代码中创建的UI元素。当我在直接在C＃中创建的UI元素上使用它时，我有以下异常：“System.ArgumentException（Value不在预期范围内。）”

我做错了什么或者这个类不允许以编程方式创建UIElement？有没有办法在Windows Phone 8.1上执行此操作？谢谢！

这是我使用的代码：

        private static async void RenderText(string text, int width, int height, int fontsize, string imagename)
    {
        RenderTargetBitmap b = new RenderTargetBitmap();

        var canvas = new Grid();

        canvas.Width = width;
        canvas.Height = height;

        var background = new Canvas();
        background.Height = width;
        background.Width = height;

        SolidColorBrush backColor = new SolidColorBrush(Colors.Red);
        background.Background = backColor;

        var textBlock = new TextBlock();
        textBlock.Text = text;
        textBlock.FontWeight = FontWeights.Bold;
        textBlock.TextAlignment = TextAlignment.Left;
        textBlock.HorizontalAlignment = HorizontalAlignment.Center;
        textBlock.VerticalAlignment = VerticalAlignment.Stretch;
        textBlock.Margin = new Thickness(35);
        //textBlock.Width = b.PixelWidth - textBlock.Margin.Left * 2;
        textBlock.TextWrapping = TextWrapping.Wrap;
        textBlock.Foreground = new SolidColorBrush(Colors.White); //color of the text on the Tile
        textBlock.FontSize = fontsize;

        canvas.Children.Add(textBlock);

        await b.RenderAsync(background);
        await b.RenderAsync(canvas);

        // Get the pixels

        var pixelBuffer = await b.GetPixelsAsync();


        // Get the local folder.
        StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;

        // Create a new folder name DataFolder.
        var dataFolder = await local.CreateFolderAsync("DataFolder",
            CreationCollisionOption.OpenIfExists);

        StorageFile file = await dataFolder.CreateFileAsync(imagename, CreationCollisionOption.ReplaceExisting);


        // Encode the image to the selected file on disk
        using (var fileStream = await file.OpenStreamForWriteAsync())
        {

            var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, fileStream.AsRandomAccessStream());

            encoder.SetPixelData(
                BitmapPixelFormat.Bgra8,
                BitmapAlphaMode.Ignore,
                (uint)b.PixelWidth,
                (uint)b.PixelHeight,
                DisplayInformation.GetForCurrentView().LogicalDpi,
                DisplayInformation.GetForCurrentView().LogicalDpi,
                pixelBuffer.ToArray());

            await encoder.FlushAsync();
        }
    }

Answer 1

它不仅适用于在XAML中创建的元素，但具有这些元素（MSDN says）位于VisualTree中：

将UIElement 可视树的快照呈现给图像源。

因此，如果您将元素添加到当前页面中，则您的方法将起作用：

LayoutRoot.Children.Add(canvas);

Answer 2

使用代码创建UIElemet高度和宽度值时，它们将为0。如果您想要特定分辨率的图像，请尝试为UIElement分配相同的高度和宽度。下面显示的代码对我来说效果很好。

    public static void SaveElementAsJPG(FrameworkElement element, string ImageName)
    {
        WriteableBitmap wBitmap = new WriteableBitmap(element, null);
        using (MemoryStream stream = new MemoryStream())
        {
            wBitmap.SaveJpeg(stream, (int)element.ActualWidth, (int)element.ActualHeight, 0, 100);
            wBitmap = null;
            //Use can either save the file to isolated storage or media library.
            //Creates file in Isolated Storage.
            using (var local = new IsolatedStorageFileStream(ImageName, FileMode.Create, IsolatedStorageFile.GetUserStoreForApplication()))
            {
                local.Write(stream.GetBuffer(), 0, stream.GetBuffer().Length);
            }
            //Creates file in Media Library.
            var lib = new MediaLibrary();
            var picture = lib.SavePicture(ImageName, stream.GetBuffer());
        }
    }

以编程方式在图像文件中保存UIElement的任何方法？

2 个答案: