ItemsControl modify Items at runtime - wpf

Question

in my Silverlight project I have the following ItemsControl :
<ItemsControl x:Name="ItemsList">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical" />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Border x:Name="brdItem" Opacity="1" MouseLeftButtonDown="brdItem_MouseLeftButtonDown">
<TextBlock x:Name="txtUsername" Text="{Binding Username}" />
</Border>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
What I want is :
When my user clicks on an item. I want all the other items Opacity set to "0.3".
When the mouse is released I want all the items to come back to their original state (Opacity="1").

Answer 1

It's very simple if to use the MVVM pattern. Add the Opacity property to the item class and bind it to the Border.Opacity property:
<Border x:Name="brdItem" Opacity="{Binding Opacity}" MouseLeftButtonDown="brdItem_MouseLeftButtonDown">
<TextBlock x:Name="txtUsername" Text="{Binding Username}" />
</Border>
The item class:
public class ItemViewModel : INotifyPropertyChanged
{
public string Username { get; set; }
private double _opacity;
public double Opacity
{
get { return _opacity; }
set
{
_opacity = value;
RaisePropertyChanged("Opacity");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void RaisePropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
After that your mouse event will look so:
public void brdItem_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
var vm = ((FrameworkElement)sender).DataContext as ItemViewModel;
if (vm != null)
{
vm.Opacity = 1;
this.ItemsList.ItemsSource.OfType<ItemViewModel>()
.Where(item => item != vm)
.ToList()
.ForEach(item => item.Opacity = 0.3);
}
}
To return back to the initial state use the following code:
this.ItemsList.ItemsSource.OfType<ItemViewModel>()
.ToList().ForEach(item => item.Opacity = 1);