PickContext doesn't work correctly in a wpf application

PickContext is needed to set a RhinoView before using .But for a viewport in a wpf application using Rhino.Inside, the ParentView property is Null. I use ActiveView to replace it . But another problem comes up. When the viewport is parallel , it works. When the viewport is perspective , the pickcontext dosent work correctly when magnify the viewport . Here is my code, “Viewport.Magnify(magnificationFactor, false)” is to keep the camera length. Once I do so, it work incorrectly.

 protected override void OnMouseWheel(MouseEventArgs e)
            if (HostUtils.RunningInRhino)
                double magnificationFactor = 1.0 / ViewSettings.ZoomScale;
                magnificationFactor *= magnificationFactor;
                magnificationFactor *= (e.Delta < 0) ? -1.0 : 1.0;
                if (magnificationFactor < 0.0)
                    magnificationFactor = -1.0 / magnificationFactor;
                Viewport.Magnify(magnificationFactor, true);
                    PickStyle = PickStyle.PointPick,
                    PickLine = frustumLine,
                    View = RhinoDoc.ActiveDoc.Views.ActiveView,
                    PickMode = PickMode.Shaded
                    var pickTransform = vp.GetPickTransform(e.Location);

It works correctly in parallel view.

Help Please…

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