Question

When a WPF item is frozen, the docs says it cannot be changed. I’m just not very sure what “change” mean by in this context.

For example, if I create an instance of a shape and then freeze it, is it possible to do things like rotate or translate it even though it is frozen?

Answer 1

Short answer:

Once an object is frozen, you cannot modify any properties on it. This applies recursively.

Longer answer:

First of all, the Shape class (and thus Path, Ellipse, Rectangle etc.) are not freezable.

But assuming you are talking about Geometry, which is freezable, then the general answer is no, because attempting to modify properties of a frozen object is not possible. For example, the following code will throw an exception

var geo = new LineGeometry();
geo.Freeze();
// InvalidOperationException:
geo.Transform = new TranslateTransform(10, 10);

And freezing is recursive, so its not possible to cheat the system like this:

var tx = new TranslateTransform(10, 10);
var geo = new LineGeometry();
geo.Transform = tx;
geo.Freeze();
// InvalidOperationException:
tx.X = 20;

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But, back to your original question about shapes, which are constructed out of geometries (but doesn’t derive from them).

You can freeze the geometry of your shape, and still apply transformations to that shape. This works because the transform is on the shape object, and not on the freezable:

var geo = new LineGeometry(new Point(0,0), new Point(10,10));
geo.Freeze();
var myShape = new Path { Data = geo };
// This is fine, even though the geometry is frozen
myShape.RenderTransform = new TranslateTransform(10, 10);