Animating parts of a custom FrameworkElement (OnRender and DoubleAnimation question)

My diagramming application uses custom controls and is somewhat similar
(in appearance, at least) to the class-designer in VS2005. The
overriden OnRender works well but now I want to animate the
collapse/expand behavior of the 'class shape'. I was able to implement
it in XAML but porting it to code is somewhat difficult. In particular,
the public expand method:

public void Expand()
{
expanded = true;
this.InvalidateVisual();
DoubleAnimation anim = new DoubleAnimation(0.0, 1.0, new
Duration(new TimeSpan(0, 0, 4)));
xrg.BeginAnimation(FrameworkElement.OpacityProperty, anim);
//xrg is a sub-element of the control
}

does not produce a visual effect. Obviously the OnRender is not called
when the sub-element is animated. How should I do this? In general, how
to animate part of a custom control?

[Thx]

From what I know if you use visual layer programming you will sacrifice some
benefits of the high level stuff - like animations, databinding etc.. Just
out of curiosity, why did you go with visuals?
--
Valentin Iliescu [MVP - Client Application Development]


"Illumineo" wrote:

> My diagramming application uses custom controls and is somewhat similar
> (in appearance, at least) to the class-designer in VS2005. The
> overriden OnRender works well but now I want to animate the
> collapse/expand behavior of the 'class shape'. I was able to implement
> it in XAML but porting it to code is somewhat difficult. In particular,
> the public expand method:
>
> public void Expand()
> {
> expanded = true;
> this.InvalidateVisual();
> DoubleAnimation anim = new DoubleAnimation(0.0, 1.0, new
> Duration(new TimeSpan(0, 0, 4)));
> xrg.BeginAnimation(FrameworkElement.OpacityProperty, anim);
> //xrg is a sub-element of the control
> }
>
> does not produce a visual effect. Obviously the OnRender is not called
> when the sub-element is animated. How should I do this? In general, how
> to animate part of a custom control?
>
> [Thx]
>
>

It seems I should use the CompositionTarget class, as the documentation
says, to
'...create custom drawings or animations based on a per-frame
callback..'
I was able to achieve what I wanted to do by replacing the custom
control by a UserControl which allowed me to have the animation in XAML
rather than in code.

In any case, what I have learned is this: you cannot trust the
rendering engine to do something for you. The intrinsic
refresh-algorithm is untouchable even if you call InvalidateVisual or
InvalidateArrange. Maybe I'm so used to the painting loop in Win32 or
Net2. The drawback of this is that it's very difficult to know what you
have to do to optimize the code in function of 'big' diagrams or
graph/diagrammatic processes.