How to make WPF DataGridCell ReadOnly?

I've encountered the same problem, the cell should be read-only in some rows but not in the others. Here is a workaround solution:

The idea is to dynamically switch the CellEditingTemplate between two templates, one is the same as the one in the CellTemplate, the other is for editing. This makes the edit mode acts exactly the same as the non-editing cell although it is in edit mode.

The following is some sample code for doing this, notice that this approach requires DataGridTemplateColumn:

First, define two templates for read-only and editing cells:

<DataGrid>
  <DataGrid.Resources>
    <!-- the non-editing cell -->
    <DataTemplate x:Key="ReadonlyCellTemplate">
      <TextBlock Text="{Binding MyCellValue}" />
    </DataTemplate>

    <!-- the editing cell -->
    <DataTemplate x:Key="EditableCellTemplate">
      <TextBox Text="{Binding MyCellValue}" />
    </DataTemplate>
  </DataGrid.Resources>
</DataGrid>

Then define a data template with additional ContentPresenter layer and use Trigger to switch the ContentTemplate of the ContentPresenter, so the above two templates can be switched dynamically by the IsEditable binding:

<DataGridTemplateColumn CellTemplate="{StaticResource ReadonlyCellTemplate}">
  <DataGridTemplateColumn.CellEditingTemplate>
    <DataTemplate>
      <!-- the additional layer of content presenter -->
      <ContentPresenter x:Name="Presenter" Content="{Binding}" ContentTemplate="{StaticResource ReadonlyCellTemplate}" />
      <DataTemplate.Triggers>
        <!-- dynamically switch the content template by IsEditable binding -->
        <DataTrigger Binding="{Binding IsEditable}" Value="True">
          <Setter TargetName="Presenter" Property="ContentTemplate" Value="{StaticResource EditableCellTemplate}" />
        </DataTrigger>
      </DataTemplate.Triggers>
    </DataTemplate>
  </DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>

HTH

There is a property on DataGridCell.IsReadOnly that you might think you can bind to,
e.g. using XAML like this:

<!-- Won't work -->
<DataGrid Name="myDataGrid" ItemsSource="{Binding MyItems}">
    <DataGrid.Resources>
        <Style TargetType="DataGridCell">
            <Setter Property="IsReadOnly" Value="{Binding MyIsReadOnly}" />
        </Style>
    </DataGrid.Resources>
    <!-- Column definitions... -->
</DataGrid>

Unfortunantly this won't work because this property is not writable.
Next you might attempt to intercept and stop mouse events, but this won't prevent the user from entering edit mode using the F2 key.

The way I sloved this was by listening for the PreviewExecutedEvent on the DataGrid and then conditionally flagging it as handled.
E.g. by adding code similar to this to the constructor of my Window or UserControl (or another more suitable place):

myDataGrid.AddHandler(CommandManager.PreviewExecutedEvent,
    (ExecutedRoutedEventHandler)((sender, args) =>
{
    if (args.Command == DataGrid.BeginEditCommand)
    {
        DataGrid dataGrid = (DataGrid) sender;
        DependencyObject focusScope = FocusManager.GetFocusScope(dataGrid);
        FrameworkElement focusedElement = (FrameworkElement) FocusManager.GetFocusedElement(focusScope);
        MyRowItemModel model = (MyRowItemModel) focusedElement.DataContext;
        if (model.MyIsReadOnly)
        {
            args.Handled = true;
        }
    }
}));

By doing it like this the cells are still focusable and selectable.
But the user will not be able to enter edit mode unless your model items allow it for the given row.
And you will not suffer the performance costs or complexities by using the DataGridTemplateColumn.

After much searching and experimentation using IsTabStop = False and Focusable = False works best for me.

<DataGridTextColumn Header="My Column" Binding="{Binding Path=MyColumnValue}">
    <DataGridTextColumn.CellStyle>
        <Style TargetType="DataGridCell">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=ReadOnly}" Value="True">
                    <Setter Property="IsTabStop" Value="False"></Setter>
                    <Setter Property="Focusable" Value="False"></Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </DataGridTextColumn.CellStyle>
</DataGridTextColumn>