Can DotVVM GridView columns be defined dynamically?

Question

Is it possible to create a DotVVM GridView (Business Pack and Bootstrap versions OK) with the columns dynamically defined?

I am modernizing an application where some pages use grids that are customized with what columns to include and some properties (display order, data type, etc.) stored in a database. The current version adds columns to the (ASP.NET) grid at run time in the code-behind. Is there some way I can achieve the same effect with a DotVVM GridView?

Answer 1

Yes it is certainly possible. I won't provide an exact code you can, because the solution depends on what exactly you need to do, but I'll try my best.

You can place the logic in ViewModel.Load or create a custom control that will be a wrapper for the GridView.

First, you need to get a reference to the GridView. If you choose to make a control, just use (GridView)this.Children.Single(). To make it work in viewmodel, add an ID=Something to your GridView and then call (GridView)Context.View.FindControlByClientId("Something").

The GridView (both the one from DotVVM.Framework and the one from BusinessPack) has a Columns property and you can append whatever you want to it.

grid.Columns.Add(
    new GridViewTextColumn() {
        HeaderText= "Property 1",
        ValueBinding = ...
    }
);

You will also have to create the value binding expression which is slightly tricky. Problem is that DotVVM want's the bindings to be compiled before they are put into the control, but for the compilation you need to know the exact data context of the control - it's a bit of an chicken and egg problem. You'll need a BindingCompilationService for that, you can either use constructor injection and take it from the DI container, or just call var bindingService = Context.Services.GetRequiredService<BindingCompilationService>(). To get the desired data context, use this magic spell:

var dataContext = grid.GetValueBinding(GridView.DataSourceProperty)
    .GetProperty<CollectionElementDataContextBindingProperty>().DataContext;

Then creating the binding and the grid columns is going to be fairly easy:

grid.Columns.Add(
    new GridViewTextColumn() {
        HeaderText= "Property 1",
        ValueBinding = bindingService.Cache.CreateValueBinding("_this.Property1", dataContext)
    }
);

You can do this for each of your properties. Note that CreateValueBinding helper method is relatively new, you'll definitely need DotVVM 4.0.