Question

I have made an application with a Tree and a TreeView where the user can add and remove
nodes on the fly.

I am using three different icons in the tree to mark various things by using the ordinary way of creating a StackPanel (in code not in XAML).

As it is now I have to load these icons for each of the nodes I add from the file system which consumes a lot of resources and memory because I can not find a way of “reusing” the icons between the nodes in the tree.

I tried to create three default images at start but I could only use them for three nodes, the fourth node complain and said that the item (the image) was already in use.

I have seen on the internet some possibilities of creating a ImageList but those seems to be TreeViewitem related which mean that I have to create a new ImageList for each node?

Or can the same ImageList be reused between all nodes?

Answer 1

Sounds to me that you need to call .Freeze() on your images.

Although, I have a similar case in my app and this is how I have done it (without using .Freeze()):
XAML:

    <TreeView Name="treeViewFolders" SelectedItemChanged="treeViewFolders_SelectedItemChanged" TreeViewItem.Expanded="treeViewFolders_Expanded" Margin="0,4,0,6">
        <TreeView.Resources>
            <Style TargetType="{x:Type TreeViewItem}">
                <Setter Property="HeaderTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal" Margin="0,2">
                                <Image x:Name="img" Stretch="None" RenderOptions.BitmapScalingMode="NearestNeighbor" 
                                       Source="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=TreeViewItem}, Path=DataContext}"/>
                                <TextBlock Text="{Binding}" Margin="5,0,10,0" />
                            </StackPanel>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </TreeView.Resources>
    </TreeView>

c# code:

private readonly System.Collections.Generic.Dictionary<string, ImageSource> typeIcons = new Dictionary<string, ImageSource>();

private void Window_Loaded(object sender, RoutedEventArgs e)
{
        this.typeIcons.Add("winhdd", new BitmapImage(new Uri("Images/Icons/winhdd.png", UriKind.Relative)));
        this.typeIcons.Add("harddrive", new BitmapImage(new Uri("Images/Icons/hdd.png", UriKind.Relative)));
        this.typeIcons.Add("removable", new BitmapImage(new Uri("Images/Icons/removablehdd.png", UriKind.Relative)));
        this.typeIcons.Add("folder", new BitmapImage(new Uri("Images/Icons/folder.png", UriKind.Relative)));
}

Where I’m creating my nodes (as an example):

TreeViewItem item = new TreeViewItem();
item.DataContext = this.typeIcons["harddrive"];