public InjectionDelegateConstraint(Viewport2D masterViewport, ViewportConstraintCallback callback)
		{
			if (callback == null)
				throw new ArgumentNullException("callback");
			if (masterViewport == null)
				throw new ArgumentNullException("masterViewport");

			this.callback = callback;
			this.masterViewport = masterViewport;
			masterViewport.PropertyChanged += masterViewport_PropertyChanged;
		}
        public InjectionDelegateConstraint(Viewport2D masterViewport, ViewportConstraintCallback callback)
        {
            if (callback == null)
            {
                throw new ArgumentNullException("callback");
            }
            if (masterViewport == null)
            {
                throw new ArgumentNullException("masterViewport");
            }

            this.callback                   = callback;
            this.masterViewport             = masterViewport;
            masterViewport.PropertyChanged += masterViewport_PropertyChanged;
        }