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PropertyMetadata.IsSealed Property

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.

Namespace:  System.Windows
Assembly:  WindowsBase (in WindowsBase.dll)
protected bool IsSealed { get; }

Property Value

Type: System.Boolean
true if the metadata instance is immutable; otherwise, false.

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.

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 != true) _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 == false)
        {//if not set, revert to base 
            this.SupportsMyFeature = mcpm.SupportsMyFeature;
        }
    }
}

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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