Question

I would like to assign datacontext and static values in a single Combobox. I tried like this,

this.courseList.DataContext = ldc.Courses.OrderBy(x => x.CourseID);
this.courseList.Items.Add("All");
this.courseList.Items.Add("Others");

But, it shows InvalidOperationException was Unhandeled that Items collection must be empty before using ItemsSource.

Then I tried like this,

this.courseList.Items.Add("All");       
foreach (var items in ldc.Courses.OrderBy(x => x.CourseID))
 {
   this.courseList.Items.Add(items);
 }
this.courseList.Items.Add("Others");       

It works like this Image

Since I used an ItemTemplate in XAML design for this Combobox so it doesn’t shows exactly in my way for this two value All and Others.

Here is the ItemTemplate

    <DataTemplate x:Key="CourseTemplate">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding Path=CourseID}"/>
            <TextBlock Text=" : "/>
            <TextBlock Text="{Binding Path=CourseName}"/>
        </StackPanel>
    </DataTemplate>

...
 <ComboBox Name="courseList" VerticalAlignment="Top" SelectionChanged="courseList_SelectionChanged" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding}" ItemTemplate="{StaticResource CourseTemplate}"/>

I want it to view according to DataTemplate for database entries and simple strings All and Others for All and Others respectively like the image below.

Any suggestions. Thank you.

Answer 1

As the error says, you can only use ItemsSource or Items directly, not a mix of the two. Since you essentially have two different types of data that you want to show differently you can add them all to a single bound collection and then let the templates do the work of rendering them differently. Step 1 is to build the single collection:

this.courseList.ItemsSource = new object[] { "All" }.Concat(ldc.Courses.OrderBy(x => x.CourseID)).Concat(new[] { "Others" });

You now have 2 types of data in the collection: String and your object which I’ll assume is Course. The strings will show up as you want without any extra work but you need to apply the DataTemplate only to the Course objects. The simplest way is just to replace your x:Key with a DataType:

<DataTemplate DataType="{x:Type data:Course}">
    <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding Path=CourseID}"/>
        <TextBlock Text=" : "/>
        <TextBlock Text="{Binding Path=CourseName}"/>
    </StackPanel>
</DataTemplate>

where the data xmlns corresponds to your Course object’s namespace.

Next just remove the ItemTemplate attribute from your ComboBox and you should get what you’re looking for.

If you have other places in the same scope where you’re also binding Course objects but want them to display differently you can either scope the DataType template more locally (i.e. a Grid.Resources) or use a DataTemplateSelector on your ComboBox.