MVVM WPF Combobox: creating a template for comboboxitem - wpf

Question

I have a WPF combobox which is populated from code-behind.
Code-behind (xaml.cs):
namespace WpfApplication1
{
private ObservableCollection<TransportType> transportTypes = new ObservableCollection<TransportType>();
transportTypes.Add(new TransportType() {Icon = Properties.Resources.Air, ValueMember = "A100", DisplayMember = "By Air" });
transportTypes.Add(new TransportType() {Icon = Properties.Resources.Maritime, ValueMember = "M200", DisplayMember = "Maritime" });
this.ComboBoxTransportTypes.ItemsSource = transportTypes;
}
TransportType class:
namespace WpfApplication1
{
public class TransportType
{
public Image Icon
{
get;
set;
}
public string DisplayMember
{
get;
set;
}
public string ValueMember
{
get;
set;
}
}
}
View:
<ComboBox x:Name="ComboBoxTransportTypes"
Grid.Column="1"
ItemsSource="{Binding}"
DisplayMemberPath="DisplayMember"
SelectedValuePath="ValueMember"
SelectionChanged="ComboBoxTransportTypes_SelectionChanged">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
Now I am trying to apply a ComboBox ItemTemplate and bound to the "transportTypes" collection. I would like each combobox item to be as below:
<ComboBoxItem>
<StackPanel Orientation="Horizontal">
<Image Source="{Binding bind-icon-here}" />
<TextBlock Foreground="AliceBlue"
VerticalAlignment="Center"
Text="{Binding bind-DisplayMember-here}"/>
</StackPanel>
</ComboBoxItem>
So how can I create the above combobox item template bound to my collection in order to each item to be presented with an icon followed by a string?
I have tried below but it does not work. I also do not know how to bind each item in the collection to the image and textblock within stackpanel, I have done as below but only string is displayed and not icon.
<ComboBox x:Name="ComboBoxTransportTypes"
Grid.Column="1"
ItemsSource="{Binding}"
DisplayMemberPath="DisplayMember" <-- removed from here as I cannot define DisplayMemberPath and item template at the same time.
SelectedValuePath="ValueMember"
SelectionChanged="ComboBoxTransportTypes_SelectionChanged">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
<ComboBox.ItemTemplate>
<DataTemplate DataType="l:TransportType">
<StackPanel Orientation="Horizontal">
<Image Source="{Binding Icon}" />
<TextBlock Foreground="AliceBlue"
VerticalAlignment="Center"
Text="{Binding DisplayMember}"/>
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Also, in MVVM is it better to populate combobox from code-behind as I have done here or from view model constructor?

Answer 1

The problem is that you're setting the ItemSource in both the XAML and in the code behind. If you remove ItemSource="{Binding}" from the XAML then it should work.
If you are using MVVM, the collection should be populated in the view model, not in the code behind. There should be very little code in your code behind - only things related to the view should go there (such as displaying a child window).

Answer 2

The problem is that Image.Source takes an ImageSource not an Image. Change ...
<Image Source="{Binding Icon}" />
to...
<Frame Content="{Binding Icon}"/>
and things will start working.

Answer 3

you must use bottom syntax for custom template ComboBox
<TextBlock Text="{Binding Path=DisplayMember}"/>
or
<Image Source="{Binding Path=Icon}" />
in wpf list tags like combobox,listbox,... for custom tamplate like DataTemplate you must use Path