将FrameworkElement及其DataContext保存到图像文件不会成功

问题描述

我有一个名为UserControl1的简单UserControl，其中包含一个TextBlock：

I have a simple UserControl called UserControl1 that contains a TextBlock:

  <UserControl x:Class="WpfApplication2.UserControl1"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         mc:Ignorable="d"
         d:DesignHeight="300" d:DesignWidth="300">
     <Grid>
         <TextBlock Text="{Binding}"/>
     </Grid>
</UserControl>

我初始化了它的新实例，并在代码中为其提供了DataContext。当窗口关闭时，我必须将此控件绘制到图像文件。
UserControl不会在已创建的文件中渲染边界文本。

I initialized a new instance of it and gave it a DataContext in code. when the window is closing I have to draw this control to an image file.The UserControl does not render the bounded text in the file that been created.

这是我使用用户控件的代码：

and this is my code using the usercontrol:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        Closing += MainWindow_Closing;
    }

    void MainWindow_Closing(object sender, CancelEventArgs e)
    {
        UserControl1 uc = new UserControl1();
        uc.DataContext = "hello";
        uc.Height = 100;
        uc.Width = 100;
        uc.Background = Brushes.LightBlue;
        DrawToImage(uc);
    }

    private void DrawToImage(FrameworkElement element)
    {
        element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
        element.Arrange(new Rect(element.DesiredSize));

        RenderTargetBitmap bitmap = new RenderTargetBitmap((int)element.Width, (int)element.Height,
                                                           120.0, 120.0, PixelFormats.Pbgra32);
        bitmap.Render(element);

        BitmapEncoder encoder = new PngBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(bitmap));

        using (Stream s = File.OpenWrite(@"C:\555.png"))
        {
            encoder.Save(s);
        }
    }
}

我希望这很清楚，任何帮助将不胜感激。

I Hope It's clear enough, any help will be very appreciated.

推荐答案

您只是忘了在手动测量/排列后，在控件上强制进行Layout更新（

You just forgot to force a Layout update on your control after manually Measuring/Arrangeing it (which will not be enough to force binding resolving).

对使其起作用：

private void DrawToImage(FrameworkElement element)
{
    element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
    element.Arrange(new Rect(element.DesiredSize));
    element.UpdateLayout();

    RenderTargetBitmap bitmap = new RenderTargetBitmap((int)element.Width, (int)element.Height,
                                                        120.0, 120.0, PixelFormats.Pbgra32);
    bitmap.Render(element);

    BitmapEncoder encoder = new PngBitmapEncoder();
    encoder.Frames.Add(BitmapFrame.Create(bitmap));

    using (Stream s = File.OpenWrite(@"C:\555.png"))
    {
        encoder.Save(s);
    }
}

编辑：有关绑定何时解决的更多信息：

Edit : More on when bindings are resolved : link

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