dotnet/wpf · error · ArgumentException

SR.MustNotTemplateUnassociatedControl

Error message

SR.MustNotTemplateUnassociatedControl

What it means

ControlTemplate.ValidateTemplatedParent throws this ArgumentException when the control being templated does not have this exact template registered as its TemplateInternal. A ControlTemplate can only be applied to the control instance(s) it was created for via the template system, not re-used ad hoc on unassociated controls.

Solutions

  1. Apply the template via a Style setter or as a shared resource so each control gets its own template instance through the normal resolution path.
  2. Never assign controlA.Template to controlB directly; instead re-resolve the template resource for the second control.
  3. If templating in code, create a new ControlTemplate instance for each control.

Example fix

// before
otherControl.Template = button1.Template;
// after
otherControl.Template = (ControlTemplate)FindResource("MyButtonTemplate");
Defensive patterns

Strategy: type-guard

Validate before calling

if (control.TemplateInternal != null && control.TemplateInternal != template) { /* template not associated */ }

Type guard

bool IsAssociated(ControlTemplate t, Control c) => ReferenceEquals(c.TemplateInternal, t);

Try / catch

try { other.Template = someTemplate; } catch (ArgumentException) { other.Template = (ControlTemplate)FindResource("tpl"); }

Prevention

When it happens

Trigger: Manually assigning one control's ControlTemplate instance to a different control's Template/TemplateInternal; sharing a single template instance across controls in code instead of using a Style or the template resource system.

Common situations: Code-behind that copies control.Template from one element to another; reusing a template instance built for one control; framework-internal invalidation passing the wrong templated parent.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/066053f12a802ba3. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/ControlTemplate.cs:73

        ///     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
        {
            get {  return _targetType; }
            set
            {
                ValidateTargetType(value, "value");
                CheckSealed();

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