PropertyMetadata.IsSealed Property
Definition
Important
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Gets a value that determines whether the metadata has been applied to a property in some way, resulting in the immutable state of that metadata instance.
protected:
property bool IsSealed { bool get(); };protected bool IsSealed { get; }member this.IsSealed : boolProtected ReadOnly Property IsSealed As BooleanProperty Value
true if the metadata instance is immutable; otherwise, false.
Examples
The following example checks IsSealed prior to a set operation of a custom metadata property.
public Boolean SupportsMyFeature
{
get { return _supportsMyFeature; }
set { if (!this.IsSealed) _supportsMyFeature = value; } //else may want to raise exception
}
protected override void Merge(PropertyMetadata baseMetadata, DependencyProperty dp)
{
base.Merge(baseMetadata, dp);
MyCustomPropertyMetadata mcpm = baseMetadata as MyCustomPropertyMetadata;
if (mcpm != null)
{
if (!this.SupportsMyFeature)
{//if not set, revert to base
this.SupportsMyFeature = mcpm.SupportsMyFeature;
}
}
}
Remarks
Various properties of PropertyMetadata, such as DefaultValue, are defined in the object model as read-write. This is so those properties can be adjusted after initialization of the PropertyMetadata object itself. However, once the metadata is applied to a dependency property as part of a call to Register, AddOwner, or OverrideMetadata, the property system will seal that metadata instance and the properties are now considered immutable. At the time of one of these calls, OnApply is called, and the value of this property is set to true.
