XAML from file as element - wpf

Question

Hi i want to load my element during program start from external file.
Below is my code:
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:FromFile3d" x:Class="FromFile3d.MainWindow"
Title="MainWindow" Height="400" Width="800">
<Grid>
<Grid.Background>
<LinearGradientBrush EndPoint="0.789,0.541" StartPoint="0.225,0.543">
<GradientStop Color="Black" Offset="0.849"/>
<GradientStop Color="#FF232323" Offset="1"/>
</LinearGradientBrush>
</Grid.Background>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="527*"/>
<ColumnDefinition Width="265*"/>
</Grid.ColumnDefinitions>
<Button Content="Button" Grid.Column="1" HorizontalAlignment="Left" Height="26" Margin="161,28,0,0" VerticalAlignment="Top" Width="75"/>
<Viewport3D x:Name="_viewport3D" />
</Grid>
and for last cs with load method
private void LoadCore()
{
string path = System.IO.Path.Combine(Directory.GetCurrentDirectory(), "test.xaml");
if (path != null)
{
try
{
StreamReader mysr = new StreamReader(path);
_viewport3D= XamlReader.Load(mysr.BaseStream) as Viewport3D;
}
catch (Exception e)
{
MessageBox.Show(
String.Format("Unable to parse file:\r\n\r\n{0}",
e.Message), "Error", MessageBoxButton.OK, MessageBoxImage.Error);
}
}
}
and file that i want to load is Viewport3d definition with my scene and model and ends with /Viewport3D ( i couldn't paste it, don't know why )
What i'm doing wrong ? because nothing happens when program starts my model is invisible :> (it's not the problem with viewport code because it work's fine before moving to external file).

Answer 1

_viewport3D = XamlReader.Load(mysr.BaseStream) as Viewport3D;
You can't manipulate the control tree like that. You should instead be appending elements.
First, remove the Viewport3D from your XAML.
Second, give your grid a name, say _grid.
Third, change the aforementioned line to:
_grid.Children.Add(XamlReader.Load(mysr.BaseStream) as Viewport3D);
This is the appropriate way to manipulate the control tree.