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To make an activity’s display name readonly, it isn’t enough to use the ReadOnlyAttribute on the DisplayName. In order to do this, create a custom PropertyValueEditor that displays a string in a text block, then declare an editor attribute on the “DisplayName” property of your activity. The following code demonstrates how to create a read-only custom PropertyValueEditor.

public class ReadOnlyStringEditor : PropertyValueEditor
{
    public ReadOnlyStringEditor()
    {
        FrameworkElementFactory factory = new FrameworkElementFactory(typeof(TextBlock));
        factory.SetBinding(TextBlock.TextProperty, new Binding("Value"));
        this.InlineEditorTemplate = new DataTemplate();
        this.InlineEditorTemplate.VisualTree = factory;
    }
}

The following code demonstrates how to assign the custom property editor. This should be done in the constructor for the designer.\

// Add attribute onto MyCustomActivity.DisplayName
AttributeTableBuilder builder = new AttributeTableBuilder();
builder.AddCustomAttributes(typeof(Activity), "DisplayName", new EditorAttribute(typeof(ReadOnlyStringEditor), typeof(PropertyValueEditor)));
MetadataStore.AddAttributeTable(builder.CreateTable());

Finally, assign the display name in the custom activity’s constructor.

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this.DisplayName = "Custom Sequence Activity";