dotnet/wpf · error · ArgumentException

SR.TemplateTargetTypeMismatch

Error message

SR.TemplateTargetTypeMismatch

What it means

ControlTemplate.ValidateTemplatedParent throws this ArgumentException when a ControlTemplate is applied to a control whose type does not match the template's TargetType. WPF requires the template's declared target type to be an instance of (compatible with) the control being templated. This guards against applying, say, a Button template to a CheckBox.

Solutions

  1. Set the ControlTemplate's TargetType to the actual control type being templated (or a base type of it).
  2. If the template is meant to be shared, define it with a shared base type like Control as TargetType and use TemplateBinding only on base-class properties.
  3. Fix the Style Setter or implicit style key so the template is applied only to the intended control type.

Example fix

<!-- before -->
<ControlTemplate TargetType="Button">...</ControlTemplate> <!-- applied to CheckBox -->
<!-- after -->
<ControlTemplate TargetType="CheckBox">...</ControlTemplate>
Defensive patterns

Strategy: validation

Validate before calling

if (template.TargetType != null && !template.TargetType.IsInstanceOfType(control)) throw new InvalidOperationException("Template TargetType does not match control");

Type guard

bool IsTemplateCompatible(ControlTemplate t, Control c) => t.TargetType == null || t.TargetType.IsInstanceOfType(c);

Prevention

When it happens

Trigger: Applying a ControlTemplate with TargetType=Button to a non-Button control; assigning the template via Style or directly to a control of an incompatible type before ValidateTemplatedParent runs.

Common situations: Copy-pasting a template between controls without updating TargetType; implicit style keys mismatched with the control type; refactoring a control's base class while the template TargetType still names the old type.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e19e5cfc6f9ad231. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/ControlTemplate.cs:67

        #region PublicMethods

        /// <summary>
        ///     Validate against the following rules
        ///     1. One cannot use a ControlTemplate to template a FrameworkContentElement
        ///     2. One cannot use a ControlTemplate to template a FrameworkElement other than a Control
        ///     3. One cannot use a ControlTemplate to template a Control that isn't associated with it
        /// </summary>
        protected override void ValidateTemplatedParent(FrameworkElement templatedParent)
        {
            // Must have a non-null feTemplatedParent
            ArgumentNullException.ThrowIfNull(templatedParent);

            // The target type of a ControlTemplate must match the 
            // type of the Control that it is being applied to
            if (_targetType != null && !_targetType.IsInstanceOfType(templatedParent))
            {
                throw new ArgumentException(SR.Format(SR.TemplateTargetTypeMismatch, _targetType.Name, templatedParent.GetType().Name));
            }

            // One cannot use a ControlTemplate to template a Control that isn't associated with it
            if (templatedParent.TemplateInternal != this)
            {
                throw new ArgumentException(SR.MustNotTemplateUnassociatedControl);
            }
        }
        #endregion PublicMethods

        #region PublicProperties

        /// <summary>
        ///     TargetType for this ControlTemplate
        /// </summary>
        [Ambient]
        [DefaultValue(null)]
        public Type TargetType

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