dotnet/wpf · error · InvalidOperationException

SR.ClearOnReadOnlyObjectNotAllowed

Error message

SR.ClearOnReadOnlyObjectNotAllowed

What it means

Thrown by DependencyObject.ClearValueCommon when ClearValue (or the SetValue path that clears) is invoked on a sealed DependencyObject (IsSealed == true), such as a frozen Freezable or a sealed style resource. Sealed objects are immutable by design, so clearing a property is prohibited.

Solutions

1. Check obj.IsSealed before calling ClearValue and skip or clone
2. Call obj.Clone() (or GetAsFrozen inverse: CloneCurrentValue) to obtain a mutable copy, then ClearValue on the clone
3. If it is a Freezable, work with an unfrozen copy and re-freeze after modification
4. Do not attempt to unseal the original; sealed state cannot be reversed

Example fix

// before
if (brush.IsFrozen) brush.ClearValue(Brush.OpacityProperty); // throws
// after
var mutable = brush.Clone();
mutable.ClearValue(Brush.OpacityProperty);

if (depObj.IsSealed) {
    depObj = ((Freezable)depObj).Clone(); // or skip
}
depObj.ClearValue(dp);

static bool CanClear(DependencyObject d) => !d.IsSealed;

try { depObj.ClearValue(dp); }
catch (InvalidOperationException ex) when (ex.Message.Contains("sealed") || depObj.IsSealed) { depObj = ((Freezable)depObj)?.Clone() as DependencyObject; depObj?.ClearValue(dp); }

When it happens

Trigger: Calling ClearValue(dp) on an object whose IsSealed property is true — e.g. a frozen Brush, a style-applied value on a sealed instance, or a shared resource retrieved from application resources.

Common situations: Trying to modify a frozen Freezable (Brush, Pen, Geometry) fetched from a resource dictionary, mutating a shared system resource, templated or sealed styles.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Animation_CalculatedValueIsInvalidForProperty
• Animation_DependencyPropertyIsNotAnimatable
• CannotChangeAfterSealed
• CannotChangeAfterSealed
• InvalidOperationException()

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f44216fd2abc182d. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/DependencyObject.cs:960

            DependencyProperty dp;

            // Cache the metadata object this method needed to get anyway.
            PropertyMetadata metadata = SetupPropertyChange(key, out dp);

            EntryIndex entryIndex = LookupEntry(dp.GlobalIndex);

            ClearValueCommon(entryIndex, dp, metadata);
        }

        /// <summary>
        ///     The common code shared by all variants of ClearValue
        /// </summary>
        private void ClearValueCommon(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata)
        {
            if (IsSealed)
            {
                throw new InvalidOperationException(SR.Format(SR.ClearOnReadOnlyObjectNotAllowed, this));
            }

            // Get old value
            EffectiveValueEntry oldEntry = GetValueEntry(
                                        entryIndex,
                                        dp,
                                        metadata,
                                        RequestFlags.RawEntry);

            // Get current local value
            // (No need to go through read local callback, just checking
            // for presence of Expression)
            object current = oldEntry.LocalValue;

            // Get current expression
            Expression currentExpr = (oldEntry.IsExpression) ? (current as Expression) : null;

            // Inform value expression of detachment, if applicable

View on GitHub (pinned to 81131a70a4)