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How to Reposition a Silverlight Child Window?

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21 Nov 2010CPOL2 min read 29.9K   3   4
How to Reposition a Silverlight Child Window?

Sometimes, we need to reset the position of the Silverlight Child Window at the center of the screen. This is generally required when you have a static instance of the ChildWindow and you want to use the same instance to show various messages in the screen. When you load the ChildWindow for the first time, by default it loads at the screen center. But think when your user repositions that ChildWindow to a different location in the screen, closes and reopens it, what will happen?

What you will see is, the ChildWindow opens at the same location where the user closed it the last time. So, how can we reset it to the center of the screen? This small tip will help you to achieve the functionality. Read it to know more details. The code is available for use.

The Silverlight ChildWindow internally implements its Template with a Grid named “ContentRoot”. If you edit your ChildWindow Template, you will see the following code:

XML
<Grid x:Name="ContentRoot" 
      HorizontalAlignment="{TemplateBinding HorizontalAlignment}" 
      VerticalAlignment="{TemplateBinding VerticalAlignment}" 
      Height="{TemplateBinding Height}" Width="{TemplateBinding Width}"
      RenderTransformOrigin="0.5,0.5">
    <Grid.RenderTransform>
        <TransformGroup>
            <ScaleTransform/>
            <SkewTransform/>
            <RotateTransform/>
            <TranslateTransform/>
        </TransformGroup>
    </Grid.RenderTransform>
.
.
.
</Grid>

You will see, it has a Grid named “ContentRoot”, which also has RenderTransform implemented in it. The TransformGroup of the Grid.RenderTransform contains various transformations of the Grid panel like ScaleTransform, SkewTransform, RotateTransform and TranslateTransform.

Here the TranslateTransform is used to position the ChildWindow. If you can set the X and Y coordinates of the TranslateTransform of the ChildWindow, you are done.

In this post, I will show you how to achieve that. To do this, we will create an Extension class for the ChildWindow and will implement the method to center it in the screen.

Let’s have a look into the implemented class here: 

C#
/// <summary>
/// Extension class to do some extra operation with Silverlight ChildWindow.
/// </summary>
public static class ChildWindowExtensions
{
    /// <summary>
    /// Centers the Silverlight ChildWindow in screen.
    /// </summary>
    /// <param name="childWindow">The child window.
    public static void CenterInScreen(this ChildWindow childWindow)
    {
        var root = VisualTreeHelper.GetChild(childWindow, 0) as FrameworkElement;
        if (root == null) { return; }

        var contentRoot = root.FindName("ContentRoot") as FrameworkElement;
        if (contentRoot == null) { return; }

        var group = contentRoot.RenderTransform as TransformGroup;
        if (group == null) { return; }

        TranslateTransform translateTransform = null;
        foreach (var transform in group.Children.OfType<translatetransform>())
        {
            translateTransform = transform;
        }

        if (translateTransform == null) { return; }

        // reset transform
        translateTransform.X = 0.0;
        translateTransform.Y = 0.0;
    }
}

We created a static class having a static method “CenterInScreen()” which takes the instance of the ChildWindow as the parameter. From the instance of the ChildWindow, we will get the root which is nothing but a Grid. This Grid consists of another Grid named “ContentRoot”. Once you get the ContentRoot from the ChildWindow template, we can iterate through the TransformGroup to find the TranslateTransform. It is by default present in ChildWindow. Once you get the Translate Transform, change its X and Y coordinate values to ‘0’ (zero).

That’s all about it. If you want to position it somewhere else, set them there instead of ‘0’. Remember that, before doing this operation, i.e., before calling the CenterInScreen() your Child Window needs to be added in the layout. If you didn’t add the ChildWindow to the layout before calling the method, you will see the “ArgumentOutOfRangeException”:

image

The extension method will help you to call the CenterInScreen() directly from the ChildWindow instance. Hope this information will help you when you work with the same.

This article was originally posted at http://www.kunal-chowdhury.com/feeds/posts/default

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Technical Lead
India India

Kunal Chowdhury is a former Microsoft "Windows Platform Development" MVP (Most Valuable Professional, 2010 - 2018), a Codeproject Mentor, Speaker in various Microsoft events, Author, passionate Blogger and a Senior Technical Lead by profession.

He is currently working in an MNC located in India. He has a very good skill over XAML, C#, Silverlight, Windows Phone, WPF and Windows app development. He posts his findings, articles, tutorials in his technical blog (www.kunal-chowdhury.com) and CodeProject.


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QuestionMy Vote of 5 Pin
Member 94749396-Jun-13 22:42
Member 94749396-Jun-13 22:42 
GeneralMy vote of 5 Pin
Leon Cao26-Jan-11 19:41
Leon Cao26-Jan-11 19:41 
GeneralMy vote of 5 Pin
Abhijit Jana23-Nov-10 17:44
professionalAbhijit Jana23-Nov-10 17:44 
GeneralRe: My vote of 5 Pin
Kunal Chowdhury «IN»8-Jan-11 5:09
professionalKunal Chowdhury «IN»8-Jan-11 5:09 

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