How to trigger cellTemplateSelector when Items changed - wpf

Question

I have 2 templates for DataGrid's CellTemplate. When I change the items, it won't help me select the template for me, my DisplayModeTemplateSelector won't even be called!
What I'm wondering is if there is a way to trigger this CellTemplateSelector again when items changed? How to refresh CellTemplate in DataGrid or ListView When Content Changes
<DataGridTemplateColumn x:Name="colorRange"
Width="*"
Header="Color Range">
<DataGridTemplateColumn.CellTemplateSelector>
<local:DisplayModeTemplateSelector HeatMapTemplate="{StaticResource heatMapTemplate}" ThreshHoldTemplate="{StaticResource threshHoldTemplate}" />
</DataGridTemplateColumn.CellTemplateSelector>
</DataGridTemplateColumn>
I found this blog
http://dotdotnet.blogspot.com/2008/11/refresh-celltemplate-in-listview-when.html
I think this is similar with my problem, but I really can't understand him! Can anyone explain it?

Answer 1

The solution in the blog post will not work with the DataGrid control because the DataGridTemplateColumn class doesn't belong to the Visual Tree, and even when I tried to bind it to a static class, I didn't suceed because of strange exceptions after property changes.
Anyway there is two possible ways to solve this problem.
1) The easier way.
Using the ObservableCollection class.
var itemIndex = 0;
var currentItem = vm.Items[itemIndex];
//Change necessary properties
//..
vm.Items.Remove(currentItem);
vm.Items.Insert(itemIndex, currentItem);
2) The more complex way.
You can add to your item class the property which returns the object itself.
public ItemViewModel(/*...*/)
{
this.SelfProperty = this;
//...
}
public ItemViewModel SelfProperty { get; private set; }
public void Update()
{
this.SelfProperty = null;
this.OnPropertyChanged("SelfProperty");
this.SelfProperty = this;
this.OnPropertyChanged("SelfProperty");
}
After that you can use the ContentControl.ContentTemplateSelector instead of the CellTemplateSelector like this:
<DataGridTemplateColumn Header="Color Range">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<ContentControl Content="{Binding SelfProperty}" ContentTemplateSelector="{StaticResource mySelector}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
And when you change the property, call the Update method somehow:
currentItem.SomeDataProperty = "some new value";
//Or you can add this method call to the OnPropertyChanged
//so that it calls authomatically
currentItem.Update();
The reason why I've set a null value to the SelfProperty in the Update method first, is that the Selector will not update a template until the Content property is completely changed. If I set the same object once again - nothing will happen, but if I set a null value to it first - changes will be handled.

Answer 2

The easy way is to hook the Combo Box's Selection Changed event, and reassign the template selector. This forces a refresh.
In XAML (assume the rest of the DataGrid/ComboBoxColumn:
<DataGridComboBoxColumn.EditingElementStyle>
<Style TargetType="ComboBox">
<Setter Property="ItemsSource"
Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGrid}}, Path=DataContext.Gates, UpdateSourceTrigger=PropertyChanged}"/>
<EventSetter Event="SelectionChanged" Handler="GateIDChanged" />
</Style>
That refers to this DataGridTemplateColumn:
<DataGridTemplateColumn x:Name="GateParamsColumn" Header="Gate Parameters" CellTemplateSelector="{StaticResource GateParamsTemplateSelector}"></DataGridTemplateColumn>
And in the code behind:
private void GateIDChanged(object sender, SelectionChangedEventArgs eventArgs)
{
var selector = GateParamsColumn.CellTemplateSelector;
GateParamsColumn.CellTemplateSelector = null;
GateParamsColumn.CellTemplateSelector = selector;
}