Adding and removing WPF UIElements at runtime

wpf uielement
Ra. picture Ra. · Dec 18, 2010 · Viewed 10.8k times · Source

Is there a way to logically group or tag UIElements like shapes and controls added at runtime for easy removal?

For eg., I have a Grid with some (design-time) child elements and add Ellipses and TextBlocks to it at runtime. When I want to draw a different set of Ellipses and TextBlocks, I'd like to remove the original set I added. What would be an easy way to logically group these while adding them so I can just have a children.clear() or some way to identify them to remove them?

It is possible to add a tag value but there is no way to retrieve or read this while iterating through children of a control because they are of type UIElement which does not have a tag property.

Thoughts?

Answer

decyclone picture decyclone · Dec 18, 2010

A very good place to use an Attached Property.

Example:

// Create an attached property named `GroupID`
public static class UIElementExtensions
{
    public static Int32 GetGroupID(DependencyObject obj)
    {
        return (Int32)obj.GetValue(GroupIDProperty);
    }

    public static void SetGroupID(DependencyObject obj, Int32 value)
    {
        obj.SetValue(GroupIDProperty, value);
    }

    // Using a DependencyProperty as the backing store for GroupID.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty GroupIDProperty =
        DependencyProperty.RegisterAttached("GroupID", typeof(Int32), typeof(UIElementExtensions), new UIPropertyMetadata(null));
}

Usage:

public void AddChild(UIElement element, Int32 groupID)
{
    UIElementExtensions.SetGroupID(element, groupID);
    rootPanel.Children.Add(element);
}

public void RemoveChildrenWithGroupID(Int32 groupID)
{
    var childrenToRemove = rootPanel.Children.OfType<UIElement>().
                           Where(c => UIElementExtensions.GetGroupID(c) == groupID);

    foreach (var child in childrenToRemove)
    {
        rootPanel.Children.Remove(child);
    }
}

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