#173 – You Can Put Freezable Objects Into a Read-Only State

The idea of an object deriving from Freezable is that it normally is in a read/write state, but can be explicitly put into a read-only state using the Freeze method.  A frozen object can be used more efficiently in WPF because it doesn’t need to notify consumers of the object that its value has changed.

Graphical objects in WPF like brushes and 3D geometries derive from Freezable.  Initially unfrozen, a change to one of these objects results in consumers of the objects being notified of the change.

If you have an object deriving from Freezable that you don’t plan to change, you can make the object read-only using the Freeze method.

            // Freeze this object, making it read-only (since we don't plan on changing it)
            if (theBrush.CanFreeze)
                theBrush.Freeze();

After freezing the object, if you try modifying it, you’ll get an InvalidOperationException.  But WPF will be more efficient in its use of the object.