hello

ive got a canvas that is used to display polylines, and this canvas has a scaletransform that is linked to a slider, consequently the size of the canvas can increase. however when i wrap the canvas around a scrollviewer, even when the size is increased the scrollviewer cannot/wont scroll.

ive did a little reading around and know that i could give the scrollviewer a size (smaller than the canvas) and then the canvas could be scrolled. however when i do this, and i scale the canvas up, the scrollviewer still does not recognise this.
i found some articles on the web talking about how the scrollviewer does not know the size has changed? (is that correct)

is there any way i can get around this? any easy 'workarounds' or features of the new releases that solve my problem?

thanks for any help! :-)

thanks for your answer but ive tried both rendertransform and layouttransform but neither work

the code i am trying to use is:

<ScrollViewer HorizontalScrollBarVisibility="Visible">
<Canvas x:Name="testzoom" ClipToBounds="True">
<Canvas.LayoutTransform>
<ScaleTransform CenterX="0" CenterY="0" ScaleX="{Binding Value, Mode=Default, ElementName=slider2}" ScaleY="{Binding Value, Mode=Default, ElementName=slider2}"/>
</Canvas.LayoutTransform>
<Canvas Width="886" Height="333" Opacity="0.5" Style="{StaticResource myCanvasStyle}"/>
<Polyline PreviewMouseMove="graphPosition" PreviewMouseRightButtonDown="colourdown" PreviewMouseLeftButtonDown="mousedownsize" PreviewMouseLeftButtonUp="mouseupsize" Stroke="Black" StrokeThickness="5" Points="{Binding Path=lPointsPoly}"/>
</Canvas>
</ScrollViewer>

thanks again, stu

try setting some initial width and height on the canvas

You'll need to ensure you're setting your Canvas' LayoutTransform in order to inform the parent scrollviewer of the change in it's size. You are likely setting your Canvas' RenderTransform, which will work fine for your content, but occurs on Render, rather than on Layout, which is what you need.

HTH,

Fred Vandervelde

thanks for your answer but ive tried both rendertransform and layouttransform but neither work

the code i am trying to use is:

<ScrollViewer HorizontalScrollBarVisibility="Visible">
<Canvas x:Name="testzoom" ClipToBounds="True">
<Canvas.LayoutTransform>
<ScaleTransform CenterX="0" CenterY="0" ScaleX="{Binding Value, Mode=Default, ElementName=slider2}" ScaleY="{Binding Value, Mode=Default, ElementName=slider2}"/>
</Canvas.LayoutTransform>
<Canvas Width="886" Height="333" Opacity="0.5" Style="{StaticResource myCanvasStyle}"/>
<Polyline PreviewMouseMove="graphPosition" PreviewMouseRightButtonDown="colourdown" PreviewMouseLeftButtonDown="mousedownsize" PreviewMouseLeftButtonUp="mouseupsize" Stroke="Black" StrokeThickness="5" Points="{Binding Path=lPointsPoly}"/>
</Canvas>
</ScrollViewer>

thanks again, stu

try setting some initial width and height on the canvas

workaround might be to give the scrollviewer a kick in the nuts: force a measure.

thanks alot!

when i set the canvas to have initial values it worked like a treat!

so am i correct in thinking this works by the scrollviewer knowing an initial value of its child (ie canvas) and then being able to see if the value is different when the layouttransform has completed and so it knows whether to show the scroll bars or not?

It's also useful to note that you need to limit the scrollviewers size in some way (ie making it the last child in a dockpanel, with lastChildFill =true, etc) to make this work - if your scrollviewer resizes with your canvas (which can be the default behavior in some scenarios) you'll obviously never get scrollbars.

Glad you got things working.

F.