WPF change style (with trigger) programmatically - wpf

Question

I need to change the background of the selected item in a list view, programmatically.
The style currently looks like this (as default)
<Trigger Property="IsSelected" Value="True">
<Setter Property="Background">
<Setter.Value>
<ImageBrush ImageSource="images/selection-large.png"/>
</Setter.Value>
</Setter>
</Trigger>
I need to be able to change that background image of the selected item programmatically.
I have attempted to do this myself however i am not really sure how to go about it.
I did notice that the listview has a styles property but other than that i am completely stumped.
I am using VB.net
Edit
Would something like this work? and if so, what am i doing wrong? My listview is completely invisible with this code.
Dim trigger As New Trigger()
trigger.Property = ListViewItem.IsSelectedProperty
trigger.Value = True
trigger.Setters.Add(New Setter(ListViewItem.BackgroundProperty, Brushes.Pink))
mylistview.Style.Triggers.Add(trigger)
mylistview.ItemContainerStyle = Style

Answer 1

Bind your IsSelected property to some bool value in the ViewModel and toggle that.
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="IsSelected" Value="{Binding IsSelected}"/>
</Style>
</ListView.ItemContainerStyle>
Item ViewModel:
private bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
NotifyPropertyChange("IsSelected");
}
}
In WPF you don't manipulate UI elements in procedural code, instead you use DataBinding and manipulate your models / ViewModels' properties
As an aside, I recommend against using PNG or other bitmap based stuff for regular UI elements in WPF.
Instead of that you should create your UI using WPF elements which are vector-based and thus resolution independent.

Answer 2

You can do this within the XAML, Try this:
<Window.Resources>
<Style TargetType="{x:Type ListViewItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ListViewItem}">
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" SnapsToDevicePixels="true">
<ContentPresenter />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="true">
<Setter Property="Background">
<Setter.Value>
<ImageBrush ImageSource="images/selection-large.png"/>
</Setter.Value>
</Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>

Answer 3

I was able to finally work it out..
All i had to do was make another style based on the first one and give them both different x:keys.. Then i was able to change styles like this.
mylistview.ItemContainerStyle = DirectCast(FindResource("XKeyName"), Style)