在后面的代码中定义 HelixViewport3D 与在 XAML 中不同吗？

Question

There is difference when you add ModelVisual3D to HelixViewport3D defined in XAML or in code behind.

In my XAML I have:

    <Grid>
        <HelixToolkit:HelixViewport3D Name="m_helix_viewport">
        </HelixToolkit:HelixViewport3D>
    </Grid>

In code behind:

private ModelVisual3D getData() {
    ModelImporter importer = new ModelImporter();
    Model3D model = importer.Load(@"c:\test\test.obj");

    Model3DGroup group = new Model3DGroup();
    group.Children.Add(model);

    ModelVisual3D myModelVisual3D = new ModelVisual3D();
    myModelVisual3D.Content = group;
    return myModelVisual3D;
}

private void Test1() {
    /// do not render
    HelixViewport3D v = new HelixViewport3D();
    v.Children.Add(getData());
    m_helix_viewport = v;
}

private void Test2() {
    /// rendering ok
    m_helix_viewport.Children.Add(getData());
}

Question is why Test1() do not render but Test2() is ok. IMHO XAML definition is different then code definition - something is missing - but what?

Answer 1

It seems the field m_helix_viewport is just a reference to the actual instance of the control that is bound to the view. When you assign a new instance of that control to that field the reference is lost and because your new control is not bound to the view that was loaded from xaml changes to the properties of the new control doesn't affect the view. If you check out the generated code-behind file there is a method called Connect. In this method the created instances of your controls are assigned to the generated fields. In other words the instances are created by some other code and references are passed to the code-behind class.