WPF FAQ - Concepts Freezable Object

Questions and answers in this FAQ have been collected from newsgroup posts, various mailing lists and the employees of Syncfusion.

6. Concepts Freezable Object

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6.1	How can I determine whether a Freezable Is Frozen?

6.2	How can I obtain a writable copy of a Read-Only Freezable?

6.1 How can I determine whether a Freezable Is Frozen?

This example shows how to determine whether a Freezable object is frozen. If you try to modify a frozen Freezable object, it throws an 'Invalid Operation' Exception. To avoid throwing this exception, use the "IsFrozen" property of the Freezable object to determine whether it is frozen.

[C#]

Button myButton = new Button();

SolidColorBrush myBrush = new SolidColorBrush(Colors.Yellow);

if (myBrush.CanFreeze)

{

// Makes the brush unmodifiable.

myBrush.Freeze();

}

myButton.Background = myBrush;

if (myBrush.IsFrozen) // Evaluates to true.

{

// If the brush is frozen, create a clone and

// modify the clone.

SolidColorBrush myBrushClone = myBrush.Clone();

myBrushClone.Color = Colors.Red;

myButton.Background = myBrushClone;

}

else

{

// If the brush is not frozen,

// it can be modified directly.

myBrush.Color = Colors.Red;

6.2 How can I obtain a writable copy of a Read-Only Freezable?

This example shows how to use the Clone method to create a writable copy of a read-only Freezable. After a Freezable object is marked as read-only ("frozen"), you cannot modify it. However, you can use the 'Clone' method to create a modifiable clone of the frozen object.

The following example creates a modifiable clone of a frozen 'SolidColorBrush' object.

[C#]

Button myButton = new Button();

SolidColorBrush myBrush = new SolidColorBrush(Colors.Yellow);

[C#]

// Freezing a Freezable before it provides

// performance improvements if you don't

// intend on modifying it.

if (myBrush.CanFreeze)

{

// Makes the brush unmodifiable.

myBrush.Freeze();

}

myButton.Background = myBrush;

// If you need to modify a frozen brush,

// the Clone method can be used to

// create a modifiable copy.

SolidColorBrush myBrushClone = myBrush.Clone();

// Changing myBrushClone does not change

// the color of myButton, because its

// background is still set by myBrush.

myBrushClone.Color = Colors.Red;

// Replacing myBrush with myBrushClone

// makes the button change to red.

myButton.Background = myBrushClone;