How do I enable text wrapping on all column headers?

Question

Or don't bother with the primitives in the app.xaml file and do the following (my objects):

<DataGrid Name="WBdataGrid" AutoGenerateColumns="False" ColumnHeaderHeight="50" >
    <DataGrid.ColumnHeaderStyle>
        <Style TargetType="DataGridColumnHeader">
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <TextBlock TextWrapping="Wrap" Text="{Binding}"></TextBlock>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DataGrid.ColumnHeaderStyle>
    <DataGrid.Columns> ...

I would like to enable text wrapping on all column headers of my DataGrid, without disabling the other default header functionality

You need to add the following namespace to your app.xaml file:

xmlns:primitives="clr-namespace:Microsoft.Windows.Controls.Primitives;assembly=WPFToolkit"

and then add this tag to app.xaml:

<Style TargetType="{x:Type primitives:DataGridColumnHeader}">
    <Setter Property="ContentTemplate">
        <Setter.Value>
            <DataTemplate>
                <TextBlock TextWrapping="Wrap" Text="{Binding}"></TextBlock>
            </DataTemplate>
        </Setter.Value>
    </Setter>
</Style>

This will add text-wrapping to the headers of all of your DataGrids throughout your WPF application.

While we're on the subject, if you just wanted to center the text of each of your DataGrid headers, you could do this using the following style instead:

<Style TargetType="{x:Type primitives:DataGridColumnHeader}">
    <Setter Property="HorizontalContentAlignment" Value="Center"></Setter>
</Style>

Yet I've seen so many WPF articles suggesting that you can only do this by adding TextWrapping or HorizontalAlignment on each DataGrid column individually:

<toolkit:DataGridTextColumn Binding="{Binding Path=TaxAmount}">
    <toolkit:DataGridTextColumn.HeaderTemplate >
        <DataTemplate>
            <TextBlock Text="Tax Amount" Width="90" TextWrapping="Wrap" HorizontalAlignment="Center"/>
        </DataTemplate>
    </toolkit:DataGridTextColumn.HeaderTemplate>
</toolkit:DataGridTextColumn>

I added 
 to the header text where I want the text to wrap. This is useful when you don't need to bind your header text to something

<DataGridTextColumn x:Name="cAccountNumber" 
                    Header="Account&#x0a; Number" 
                    Width="80" 
                    Binding="{Binding Path=AccountNumber}" />

Instead of assigning the column name directly to the DataGridColumn.Header property, I created a TextBlock containing the column name, set the TextWrapping property of the TextBlock to "Wrap" and assigned the TextBlock to the DataGridColumn.Header property. This preserves the default header functionality.

Example:

<toolkit:DataGridTextColumn Binding="{Binding Path=MyProperty}">
    <toolkit:DataGridTextColumn.Header>
        <TextBlock Text="Something Longer" TextWrapping="Wrap" />
    </toolkit:DataGridTextColumn.Header>
</toolkit:DataGridTextColumn>

You could create a global Style for your column headers. Without any example mark-up I don't know the syntax, but it should look something like this:

<Style TargetType="{x:Type dg:ColumnHeader}">
    <Setter Property="TextWrapping" Value="Wrap"/>
</Style>

Since the Style is key-less, it will automatically be applied to all of your column headers. And styles will not override any locally set properties, so it won't "disable" any existing header functionality.