Template Resource Keys from Model

TemplateColumn<TModel> supports a resource-key constructor so model/viewmodel code can reference XAML templates by key.

Constructor Pattern

new TemplateColumn<Country>(
    "Region",
    "RegionCell",
    "RegionEditCell")

The sample project uses this pattern in multiple view models (CountriesPageViewModel, FilesPageViewModel, WikipediaPageViewModel).

Matching XAML Resources

<TreeDataGrid.Resources>
  <DataTemplate x:Key="RegionCell" DataType="m:Country">
    <TextBlock Text="{Binding Region}"/>
  </DataTemplate>
  <DataTemplate x:Key="RegionEditCell" DataType="m:Country">
    <ComboBox ItemsSource="{x:Static m:Countries.Regions}"
              SelectedItem="{Binding Region}"/>
  </DataTemplate>
</TreeDataGrid.Resources>

Runtime Resolution Model

TemplateColumn<TModel> resolves keys with anchor.FindResource(key) when template cells are realized.

Key behavior:

template lookup is lazy (first need)
resolved templates are cached
missing keys throw KeyNotFoundException
editing template is optional (if no editing key/template is supplied, the template cell remains read-only)
if an editing key is supplied but not found, edit entry triggers a KeyNotFoundException

Recommended Practices

keep key names as constants in shared code
keep templates near owning grid unless cross-grid reuse is intentional
define explicit DataType and stable bindings in each template
verify editing template exists before enabling edit-centric workflows

Troubleshooting

KeyNotFoundException for template key Cause: key does not exist or is not visible in lookup scope. Fix: place template in TreeDataGrid.Resources, parent resources, or Application.Resources.
Cell never enters editing Cause: no editing template key was provided; TemplateCell.CanEdit is false. Fix: pass editing template key (or direct editing template instance) to TemplateColumn.
Edit starts but fails with KeyNotFoundException Cause: editing key was provided, but no matching keyed DataTemplate exists in resource scope. Fix: define the editing template key in scope or remove editing-key usage.