C# – Binding DataGridTemplateColumn

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Seems I've hit a wall trying to use DataTemplates on my DataGrid. What I'm trying to do is to use one template to show two rows of text for each cell. But it doesn't seem to be possible to Bind the column in any way.

Following code hopefully shows what I wish to do. Note the Binding for each column: there is no such thing for a template column, and as such, this xaml couldn't possibly work.

<Window.Resources>
    <DataTemplate x:Key="DoubleField">
        <StackPanel>
            <TextBlock Text="{Binding Value1}"/>
            <TextBlock Text="{Binding Value2}"/>
        </StackPanel>
    </DataTemplate>
</Window.Resources>

<DataGrid>
    <DataGrid.Columns>
        <DataGridTemplateColumn CellTemplate="{StaticResource DoubleField}" Binding="{Binding Title}"/> // <- Binding does not exist for templatecolumn, I only wish it did
        <DataGridTemplateColumn CellTemplate="{StaticResource DoubleField}" Binding="{Binding Price}"/> // <- Binding does not exist for templatecolumn, I only wish it did
        <DataGridTemplateColumn CellTemplate="{StaticResource DoubleField}" Binding="{Binding Stuff}"/> // <- Binding does not exist for templatecolumn, I only wish it did
    </DataGrid.Columns>
</DataGrid>

class MyListItem {
    class DoubleItem {
        string Value1 { get; set; }
        string Value2 { get; set; }
    }    
    DoubleItem Title { get; set; }
    DoubleItem Price { get; set; }
    DoubleItem Stuff { get; set; }
}

Am I doomed to copy the whole DataTemplate to every column just to have a different binding on each copy? Surely there a nice way to go around this? Or am I just missing something blindingly obvious again?

Best Answer

I'm not completely sure what you're trying to do but if you need to get the DataContext of the whole row, you can use a RelativeSource binding to walk up the visual tree. Like so:

<DataTemplate x:Key="DoubleField">
    <StackPanel>
        <TextBlock Text="{Binding DataContext.Value1, RelativeSource={RelativeSource AncestorType=DataGridRow}}"/>
        <TextBlock Text="{Binding DataContext.Value2, RelativeSource={RelativeSource AncestorType=DataGridRow}}"/>
    </StackPanel>
</DataTemplate>

Related Solutions

WPF DataGridTemplateColumn with ComboBox Binding (MVVM pattern)

as default.kramer said, you need to remove the RelativeSource from your bindings for the SelectedItem and SelectedValue like this (notice that you should add Mode=TwoWay to your binding so that the change in the combobox is reflected in your model).

<DataGridTemplateColumn Header="House Owner">
    <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <ComboBox
                ItemsSource="{Binding Path=DataContext.Owners, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
                DisplayMemberPath="Name"
                SelectedItem="{Binding HouseOwner, Mode=TwoWay}"
                SelectedValue="{Binding HouseOwner.ID}"
                SelectedValuePath="ID"/>
        </DataTemplate>
    </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

However, unlike he said, you don't have to remove the binding for the SelectedValue. In fact, if you remove it, it won't work (both SelectedValue and SelectedValuePath should be set here, as you've done), because that's what's allowing the binding mechanism to identify the selection from the combobox to the DataGrid's HouseOwner property.

SelectedValue/SelectedValuePath combination is very interesting. SelectedValuePath tells the databinding that the ID property of the Owner object currently selected represents its value, SelectedValue tells it that that value should be bound to the HouseOwner.ID which is the selected object on the DataGrid.

Therefore, if you remove those binding, the only thing the databinding mechanism will know is "what object is selected", and to make the correspondence between the selected item in the ComboBox and the HouseOwner property on the selected item in the DataGrid, they have to be "the same object reference". Meaning that, for example, the following wouldn't work:

Owners = new ObservableCollection<Owner>
                {
                    new Owner {ID = 1, Name = "Abdou"},
                    new Owner {ID = 2, Name = "Moumen"}
                };
Houses = new ObservableCollection<House>
                {
                    new House {ID = 1, HouseOwner = new Owner {ID = 1, Name = "Abdou" }},
                    new House {ID = 2, HouseOwner = new Owner {ID = 2, Name = "Moumen"}}
                };

(notice that the "HouseOwners" of the Houses collection are different (new) from the ones in the Owners collection). However, the following would work:

Owners = new ObservableCollection<Owner>
                {
                    new Owner {ID = 1, Name = "Abdou"},
                    new Owner {ID = 2, Name = "Moumen"}
                };
Houses = new ObservableCollection<House>
                {
                    new House {ID = 1, HouseOwner = Owners[0]},
                    new House {ID = 2, HouseOwner = Owners[1]}
                };

Hope this helps :)

Update: in the second case, you can get the same result without having the references being the same by overriding Equals on the Owner class (naturally, since it's used to compare the objects in the first place). (thanks to @RJ Lohan for noting this in the comments below)

Best Answer

Related Solutions

WPF DataGridTemplateColumn with ComboBox Binding (MVVM pattern)

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