Rotation of Client Graphics C#

[Dev_rim]

Hi everyone,

I just want the rotate a client graphic object. From its center and 90 degrees. But there is not any change in view.

Here is my code

            double PI = 3.14159265358979;
            AssemblyDocument asmDoc = (AssemblyDocument)invApp.ActiveDocument;
            AssemblyComponentDefinition asmCompDef = asmDoc.ComponentDefinition;
            TransientGeometry transientGeometry = invApp.TransientGeometry;
            ClientGraphics partPreview = asmCompDef.ClientGraphicsCollection["PartPreview"];
            GraphicsNode graphicsNode = partPreview.ItemById[partPreview.Count];
            Inventor.Camera cam = invApp.ActiveView.Camera;
            Matrix matrix = transientGeometry.CreateMatrix();
            Vector vector = cam.UpVector.AsVector();
            matrix.SetToRotation(PI / 2, vector, placementPoint);
          
            graphicsNode.Transformation.TransformBy(matrix);
            invApp.ActiveView.Update();

Is any wrong with my code?

Thanks.