ContentControl + RenderTargetBitmap +空图像 [英] ContentControl + RenderTargetBitmap + empty image

问题描述

我试图创建一些图表图像，而不在屏幕上显示这些图表。我已经花了很长时间了，尝试了很多不同的方法，但是似乎没有任何效果。如果我先在窗口中显示图表，则代码可以正常工作；但是，如果我不在窗口中显示图表，则位图只是白色且带有黑色边框（不知道为什么）。

Im trying to create some chart images without ever displaying those charts on the screen. I'v been at this for quite a while and tried a lot of different things but nothing seems to work. The code works perfectly if I display the chart in a window first, but if I don't display it in a window, the bitmap is just white with a black border (no idea why).

我尝试在渲染之前将图表添加到边框，并为边框提供绿色的borderBrush。在位图中，我看到绿色的边框画笔，然后是黑色的边框和白色背景，但没有图表。该图表不包含在黑色的边界中，所以我不知道它来自哪里。

I have tried adding the chart to a border before rendering and giving the border a green borderBrush. In the bitmap, I see the green borderBrush then the black border and white background but no chart. The Chart is not contained in a black boarder so I don't know where that is coming from.

我尝试将图表添加到窗口中而不调用window.Show （）再一次，我得到了黑色寄宿生和白色背景。但是，如果我调用window.Show（），则位图将包含图表。

I have tried adding the chart to a window without calling window.Show() and again I just get the black boarder and white background. However if I call window.Show() the bitmap contains the chart.

我已尝试使用drawingVisual进行解释，如此处，结果相同。

I have tried using a drawingVisual as explained here, same result.

以下是代码（不包括将元素添加到边框或窗口中）：

Here is the code (not including adding the element to a border or window):

private static BitmapSource CreateElementScreenshot(FrameworkElement element, int dpi)
{
    if (!element.IsMeasureValid)
    {
        Size size = new Size(element.Width, element.Height);
        element.Measure(size);
        element.Arrange(new Rect(size));
    }

    element.UpdateLayout();

    var scale = dpi/96.0;

    var renderTargetBitmap = new RenderTargetBitmap
        (
            (int)(scale * element.RenderSize.Width),(int)(scale * element.RenderSize.Height),dpi,dpi,PixelFormats.Default
        );

    // this is waiting for dispatcher to perform measure, arrange and render passes
    element.Dispatcher.Invoke(((Action)(() => renderTargetBitmap.Render(element))), DispatcherPriority.Render);

    return renderTargetBitmap;
}

注意：图表为ContentControl。

Note: The chart is a ContentControl.

反正我可以在不首先显示在窗口中的情况下显示图表吗？

Is there anyway I can get the chart to render without displaying it in a window first?

推荐答案

调用element.ApplyTemplate（）可以达到目的。

Calling element.ApplyTemplate() did the trick.

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