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Freezable Class

Defines an object that has a modifiable state and a read-only (frozen) state. Classes that derive from Freezable provide detailed change notification, can be made immutable, and can clone themselves.

Namespace:  System.Windows
Assembly:  WindowsBase (in WindowsBase.dll)
public abstract class Freezable : DependencyObject

The Freezable type exposes the following members.

  NameDescription
Protected methodFreezableInitializes a new instance of a Freezable derived class.
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  NameDescription
Public propertyCanFreezeGets a value that indicates whether the object can be made unmodifiable.
Public propertyDependencyObjectTypeGets the DependencyObjectType that wraps the CLR type of this instance.  (Inherited from DependencyObject.)
Public propertyDispatcherGets the Dispatcher this DispatcherObject is associated with. (Inherited from DispatcherObject.)
Public propertyIsFrozenGets a value that indicates whether the object is currently modifiable.
Public propertyIsSealedGets a value that indicates whether this instance is currently sealed (read-only). (Inherited from DependencyObject.)
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  NameDescription
Public methodCheckAccessDetermines whether the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
Public methodClearValue(DependencyProperty)Clears the local value of a property. The property to be cleared is specified by a DependencyProperty identifier. (Inherited from DependencyObject.)
Public methodClearValue(DependencyPropertyKey)Clears the local value of a read-only property. The property to be cleared is specified by a DependencyPropertyKey. (Inherited from DependencyObject.)
Public methodCloneCreates a modifiable clone of the Freezable, making deep copies of the object's values. When copying the object's dependency properties, this method copies expressions (which might no longer resolve) but not animations or their current values.
Protected methodCloneCoreMakes the instance a clone (deep copy) of the specified Freezable using base (non-animated) property values.
Public methodCloneCurrentValueCreates a modifiable clone (deep copy) of the Freezable using its current values.
Protected methodCloneCurrentValueCoreMakes the instance a modifiable clone (deep copy) of the specified Freezable using current property values.
Public methodCoerceValueCoerces the value of the specified dependency property. This is accomplished by invoking any CoerceValueCallback function specified in property metadata for the dependency property as it exists on the calling DependencyObject. (Inherited from DependencyObject.)
Protected methodCreateInstanceInitializes a new instance of the Freezable class.
Protected methodCreateInstanceCoreWhen implemented in a derived class, creates a new instance of the Freezable derived class.
Public methodEqualsDetermines whether a provided DependencyObject is equivalent to the current DependencyObject. (Inherited from DependencyObject.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodFreeze()Makes the current object unmodifiable and sets its IsFrozen property to true.
Protected methodStatic memberFreeze(Freezable, Boolean)If the isChecking parameter is true, this method indicates whether the specified Freezable can be made unmodifiable. If the isChecking parameter is false, this method attempts to make the specified Freezable unmodifiable and indicates whether the operation succeeded.
Protected methodFreezeCoreMakes the Freezable object unmodifiable or tests whether it can be made unmodifiable.
Public methodGetAsFrozenCreates a frozen copy of the Freezable, using base (non-animated) property values. Because the copy is frozen, any frozen sub-objects are copied by reference.
Protected methodGetAsFrozenCoreMakes the instance a frozen clone of the specified Freezable using base (non-animated) property values.
Public methodGetCurrentValueAsFrozenCreates a frozen copy of the Freezable using current property values. Because the copy is frozen, any frozen sub-objects are copied by reference.
Protected methodGetCurrentValueAsFrozenCoreMakes the current instance a frozen clone of the specified Freezable. If the object has animated dependency properties, their current animated values are copied.
Public methodGetHashCodeGets a hash code for this DependencyObject. (Inherited from DependencyObject.)
Public methodGetLocalValueEnumeratorCreates a specialized enumerator for determining which dependency properties have locally set values on this DependencyObject. (Inherited from DependencyObject.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetValueReturns the current effective value of a dependency property on this instance of a DependencyObject. (Inherited from DependencyObject.)
Public methodInvalidatePropertyRe-evaluates the effective value for the specified dependency property (Inherited from DependencyObject.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodOnChangedCalled when the current Freezable object is modified.
Protected methodOnFreezablePropertyChanged(DependencyObject, DependencyObject)Ensures that appropriate context pointers are established for a DependencyObjectType data member that has just been set.
Protected methodOnFreezablePropertyChanged(DependencyObject, DependencyObject, DependencyProperty)This member supports the Windows Presentation Foundation (WPF) infrastructure and is not intended to be used directly from your code.
Protected methodOnPropertyChangedOverrides the DependencyObject implementation of OnPropertyChanged to also invoke any Changed handlers in response to a changing dependency property of type Freezable. (Overrides DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs).)
Public methodReadLocalValueReturns the local value of a dependency property, if it exists. (Inherited from DependencyObject.)
Protected methodReadPreambleEnsures that the Freezable is being accessed from a valid thread. Inheritors of Freezable must call this method at the beginning of any API that reads data members that are not dependency properties.
Public methodSetCurrentValueSets the value of a dependency property without changing its value source. (Inherited from DependencyObject.)
Public methodSetValue(DependencyProperty, Object)Sets the local value of a dependency property, specified by its dependency property identifier. (Inherited from DependencyObject.)
Public methodSetValue(DependencyPropertyKey, Object)Sets the local value of a read-only dependency property, specified by the DependencyPropertyKey identifier of the dependency property. (Inherited from DependencyObject.)
Protected methodShouldSerializePropertyReturns a value that indicates whether serialization processes should serialize the value for the provided dependency property. (Inherited from DependencyObject.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodVerifyAccessEnforces that the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
Protected methodWritePostscriptRaises the Changed event for the Freezable and invokes its OnChanged method. Classes that derive from Freezable should call this method at the end of any API that modifies class members that are not stored as dependency properties.
Protected methodWritePreambleVerifies that the Freezable is not frozen and that it is being accessed from a valid threading context. Freezable inheritors should call this method at the beginning of any API that writes to data members that are not dependency properties.
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  NameDescription
Public eventChangedOccurs when the Freezable or an object it contains is modified.
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The Freezable class provides special features that can help improve application performance when using objects that are expensive to modify or copy. Examples of Freezable objects include the following:

Deriving From Freezable

A class that derives from Freezable gains the following features:

  • Special states: a read-only (frozen) state and a writable state.

  • Thread safety: a frozen Freezable object can be shared across threads.

  • Detailed change notification: Unlike other DependencyObject objects, a Freezable object provides change notifications when sub-property values change.

  • Easy cloning: the Freezable class has already implemented several methods that produce deep clones.

For information on using and creating your own Freezable objects, see Freezable Objects Overview.

This example shows how to make a Freezable read-only by calling its Freeze method.

You cannot freeze a Freezable object if any one of the following conditions is true about the object:

  • It has animated or data bound properties.

  • It has properties that are set by a dynamic resource. For more information about dynamic resources, see the XAML Resources.

  • It contains Freezable sub-objects that cannot be frozen.

If these conditions are false for your Freezable object and you do not intend to modify it, consider freezing it to gain performance benefits.

The following example freezes a SolidColorBrush, which is a type of Freezable object.

Button myButton = new Button();
SolidColorBrush myBrush = new SolidColorBrush(Colors.Yellow);          

if (myBrush.CanFreeze)
{
    // Makes the brush unmodifiable.
    myBrush.Freeze();
}

myButton.Background = myBrush;  

For more information about Freezable objects, see the Freezable Objects Overview.

More Code

How to: Obtain a Writable Copy of a Read-Only FreezableThis example shows how to use the Clone method to create a writable copy of a read-only Freezable.
How to: Determine Whether a Freezable Is FrozenThis example shows how to determine whether a Freezable object is frozen. If you try to modify a frozen Freezable object, it throws an InvalidOperationException. To avoid throwing this exception, use the IsFrozen property of the Freezable object to determine whether it is frozen.

.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.

Any public static members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

When the IsFrozen property is false, a Freezable object can be accessed only from the thread on which it was created. Attempting to access it from another thread throws an InvalidOperationException. The Dispatcher.Invoke and Dispatcher.BeginInvoke methods provide support for marshalling to the correct thread.

When their IsFrozen property is true, Freezable objects are free-threaded. For more information, see Freezable Objects Overview.

System.Object
  System.Windows.Threading.DispatcherObject
    System.Windows.DependencyObject
      System.Windows.Freezable
        System.Windows.Controls.Ribbon.RibbonControlSizeDefinition
        System.Windows.Controls.Ribbon.RibbonGroupSizeDefinitionBase
        System.Windows.Input.InputBinding
        System.Windows.Media.Animation.Animatable
        System.Windows.Media.Animation.BooleanKeyFrame
        System.Windows.Media.Animation.BooleanKeyFrameCollection
        System.Windows.Media.Animation.ByteKeyFrame
        System.Windows.Media.Animation.ByteKeyFrameCollection
        System.Windows.Media.Animation.CharKeyFrame
        System.Windows.Media.Animation.CharKeyFrameCollection
        System.Windows.Media.Animation.ColorKeyFrame
        System.Windows.Media.Animation.ColorKeyFrameCollection
        System.Windows.Media.Animation.DecimalKeyFrame
        System.Windows.Media.Animation.DecimalKeyFrameCollection
        System.Windows.Media.Animation.DoubleKeyFrame
        System.Windows.Media.Animation.DoubleKeyFrameCollection
        System.Windows.Media.Animation.EasingFunctionBase
        System.Windows.Media.Animation.Int16KeyFrame
        System.Windows.Media.Animation.Int16KeyFrameCollection
        System.Windows.Media.Animation.Int32KeyFrame
        System.Windows.Media.Animation.Int32KeyFrameCollection
        System.Windows.Media.Animation.Int64KeyFrame
        System.Windows.Media.Animation.Int64KeyFrameCollection
        System.Windows.Media.Animation.KeySpline
        System.Windows.Media.Animation.MatrixKeyFrame
        System.Windows.Media.Animation.MatrixKeyFrameCollection
        System.Windows.Media.Animation.ObjectKeyFrame
        System.Windows.Media.Animation.ObjectKeyFrameCollection
        System.Windows.Media.Animation.Point3DKeyFrame
        System.Windows.Media.Animation.Point3DKeyFrameCollection
        System.Windows.Media.Animation.PointKeyFrame
        System.Windows.Media.Animation.PointKeyFrameCollection
        System.Windows.Media.Animation.QuaternionKeyFrame
        System.Windows.Media.Animation.QuaternionKeyFrameCollection
        System.Windows.Media.Animation.RectKeyFrame
        System.Windows.Media.Animation.RectKeyFrameCollection
        System.Windows.Media.Animation.Rotation3DKeyFrame
        System.Windows.Media.Animation.Rotation3DKeyFrameCollection
        System.Windows.Media.Animation.SingleKeyFrame
        System.Windows.Media.Animation.SingleKeyFrameCollection
        System.Windows.Media.Animation.SizeKeyFrame
        System.Windows.Media.Animation.SizeKeyFrameCollection
        System.Windows.Media.Animation.StringKeyFrame
        System.Windows.Media.Animation.StringKeyFrameCollection
        System.Windows.Media.Animation.ThicknessKeyFrame
        System.Windows.Media.Animation.ThicknessKeyFrameCollection
        System.Windows.Media.Animation.Vector3DKeyFrame
        System.Windows.Media.Animation.Vector3DKeyFrameCollection
        System.Windows.Media.Animation.VectorKeyFrame
        System.Windows.Media.Animation.VectorKeyFrameCollection
        System.Windows.Media.DoubleCollection
        System.Windows.Media.ImageMetadata
        System.Windows.Media.Int32Collection
        System.Windows.Media.Media3D.GeneralTransform2DTo3D
        System.Windows.Media.Media3D.GeneralTransform3DTo2D
        System.Windows.Media.Media3D.Point3DCollection
        System.Windows.Media.Media3D.Vector3DCollection
        System.Windows.Media.PointCollection
        System.Windows.Media.VectorCollection
        System.Windows.Shell.TaskbarItemInfo
        System.Windows.Shell.ThumbButtonInfo
        System.Windows.Shell.WindowChrome
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