CODEWITHSUNDEEP
c#wpfxamlpng
rawk_77
rawk_77

Reputation: 3

WPF getting Null error when trying to create image from XAML page

I am new to C# programming and having difficulty referencing a xaml file in a different class.

I am trying to create a program that will generate a PNG file from a Xaml page. I am able to capture the Canvas from the MainWindow.xaml, but I want to grab it from a different XAMl file called overlay.xaml.

I've added the Overlay.xaml as a page but when ever I reference it in the MainWindow.xaml.cs class I get a NULL value error. My assumption is that because the overlay.xaml page is never initialized all the values are null. How do I import, or initialize the overlay.xaml?

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public overlay overlay2;
    public MainWindow()
    {
        InitializeComponent();   
    }

    public void CaptureImage()
    {
        Rect rect = new Rect(overlay2.OverylayCanvas.RenderSize);  <--- Returns the null error
        RenderTargetBitmap rtb = new RenderTargetBitmap((int)rect.Right,
            (int)rect.Bottom, 96d, 96d, System.Windows.Media.PixelFormats.Default);
        rtb.Render(overlay2.OverylayCanvas);
        //encode as PNG
        BitmapEncoder pngEncoder = new PngBitmapEncoder();
        pngEncoder.Frames.Add(BitmapFrame.Create(rtb));

        //Save to memory
        System.IO.MemoryStream ms = new System.IO.MemoryStream();

        pngEncoder.Save(ms);
        ms.Close();
        System.IO.File.WriteAllBytes("Generated_Image.png", ms.ToArray());
        Console.WriteLine("Done");
    }
}

Overlay.xaml

<Page x:Class="WpfApplication1.overlay"
  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" 
  xmlns:local="clr-namespace:ScoreboardUpdate"
  mc:Ignorable="d" 
  d:DesignHeight="150" d:DesignWidth="500"
  Title="overlay">

<Canvas x:Name="OverylayCanvas" Canvas.Left="0" Canvas.Top="20" x:FieldModifier="public">
    <Rectangle Fill="#FFF4F4F5" Height="72" Canvas.Left="58" Stroke="Black" Canvas.Top="37" Width="258"/>
</Canvas>

Upvotes: 0

Views: 92

Answers (1)

Valentin
Valentin

Reputation: 5488

Well, you can create overlay2 in a MainWindow constructor

public overlay overlay2;

public MainWindow()
{
    InitializeComponent();   
    overlay2 = new Overlay();
}

Or you can initialize it in MainWindow.xaml file.

<Window x:Class="WpfApplication1...         
     ....
     <WpfApplication1:overlay x:Name="overlay2"></WpfApplication1:overlay>
     ....
</Window>

Then you should remove the overlay2 declaration from MainWindow.xaml.cs, because it is already declared in xaml file. 

public partial class MainWindow : Window
{
    // public overlay overlay2; <-- is already declared in xaml.

    public MainWindow()
    {
        InitializeComponent();   
    }

Upvotes: 2

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