How to show Validation Error Message on GridView level

[NayLin]

I have learned that RadGridView has data validation feature per cell and row. But in my case, I want data validation on GridView level. In my app, I have "Purchase Order Form". In this form, there is RadGridView for Purchase Order Items. The validation scenario is User must add at least one item to this RadGridView.

I use the way of Data Annotation and Validation Attribute in my ViewModel to check this validation.

[CollectionHasElements( ErrorMessage = "Purchase order must have at least one order item." )]
        public ObservableCollection<PurchaseOrderItemDecorator> PurchaseOrderItemDecorators
        {
            get { return _purchaseOrderItemDecorator; }
            set { SetProperty( ref _purchaseOrderItemDecorator, value ); }
        }

The RadGridView successfully notify the error by showing Red Border around the grid. But it somehow failed to show the error message. I attached the screenshot of this RadGridView.

In normal telerik wpf controls, it usually shows the error message on top right corner red block triangle. I wish my Gridview act like that for showing validation error message.

Thanks.

[Stefan]

Hello NayLin,

I tried achieving such behavior of the control when validating it through a ValidationAttribute, but to no avail. RadGridView performs its validation on row level, which is the expected behavior. You can check out the attached demo application as a demonstration.

As to achieving the desired result, a possible solution might be to subscribe to the CellValidating event and within the event handler set the BorderBrush of the control to "Red".  Then, you can define a property in the view model to which the ToolTip showing the error message will be bound. In order to position the ToolTip in the top right corner of RadGridView, I suggest you taking a look at this and this StackOverflow threads. You may also find this MSDN article useful on the matter.

Regards,
Stefan X1
Telerik