如何在ScrollViewer（WP7）中执行RenderTransform？

Question

I've tried many ways to manage RenderTransform within ScrollViewer (Windows Phone 7 Silverlight), but it seems to me almost impossible now. What I got is Grid with with its sizes inside ScrollViewer and I want to change grid's content size from code by RenderTransform by it do nothing!

      <ScrollViewer x:Name="scrollViewer" Width="800" Height="480" HorizontalScrollBarVisibility="Visible" VerticalScrollBarVisibility="Visible">
        <Grid x:Name="grid" Width="1600" Height="960" HorizontalAlignment="Left" VerticalAlignment="Top">
            <Grid.RenderTransform>
                <CompositeTransform x:Name="scaleTransform" ScaleX="1" ScaleY="1"/>
            </Grid.RenderTransform>
            <Image x:Name="backgroundImage" Source="/Images/backgrounds/Happy rainbow.png" Stretch="Fill"/>
        </Grid>
    </ScrollViewer>

In code:

        private void button_Click(object sender, RoutedEventArgs e)
    {
            (grid.RenderTransform as CompositeTransform ).CenterX = 0;
            (grid.RenderTransform as CompositeTransform ).CenterY = 0;
            (grid.RenderTransform as CompositeTransform ).ScaleX = 0.5;
            (grid.RenderTransform as CompositeTransform ).ScaleY = 0.5;
            grid.UpdateLayout();
    }

Binding on Scale and Visual states do nothig too. I really would appreciate your help.

Answer 1

Better idea... put your Grid content into an ItemsControl, and perform a ScaleTransform on the ItemsControl.

<Grid>
    <ItemsControl x:Name="ContentScaler">
        <Image x:Name="backgroundImage" Source="/Images/backgrounds/Happy rainbow.png" Stretch="Fill"/>
    </ItemsControl>
</Grid>

And in the code-behind...

ContentScaler.RenderTransform = new ScaleTransform() { ScaleX = 0.5, ScaleY = 0.5, CenterX = 0, CenterY = 0 };

Depending on what else you may need to do, you may need to do something like set a WrapPanel as the ItemsPanelTemplate and/or resize the ItemsControl when you do your scaling. It can get a little tricky, but hopefully this will get you pointed in the right direction.

The use of Grid in Silverlight tends to be a bit overused also, IMHO, unless one needs to break things into a table type layout. A Canvas may be better suited for what you are doing.

Answer 2

I'm not sure if this is exactly what you need but if you insert an extra grid like this...

            <ScrollViewer Grid.Row="1" x:Name="scrollViewer"
                      Width="800"
                      Height="480"
                      HorizontalScrollBarVisibility="Visible"
                      VerticalScrollBarVisibility="Visible">
            <Grid x:Name="grid"
                  HorizontalAlignment="Left"
                  VerticalAlignment="Top">
                <Grid
                    Width="1600"
                    Height="960">
                    <Grid.RenderTransform>
                        <CompositeTransform x:Name="scaleTransform"
                                            ScaleX="1"
                                            ScaleY="1" />
                    </Grid.RenderTransform>
                    <Image x:Name="backgroundImage"
                           Source="ApplicationIcon.png"
                           Stretch="Fill" />
                    </Grid>
            </Grid>
        </ScrollViewer>

at least the contents will get scaled..