How do I get design-time view of a view-model first approach with IoC? - caliburn.micro

Question

I have a MasterViewModel that contains other viewmodels.
public MasterViewModel()
{
User = new UserViewModel();
Search = new SearchViewModel();
}
When I in my MasterView add
<Window ...
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cal="http://www.caliburnproject.org"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:viewModels="clr-namespace:MyApp.ViewModels"
d:DataContext="{d:DesignInstance viewModels:MasterViewModel, IsDesignTimeCreatable=True}"
cal:Bind.AtDesignTime="True"
mc:Ignorable="d"
>
<ContentControl x:Name="User" />
<ContentControl x:Name="Search" />
I can see the content controls at design time.
Now, I would like to add the viewmodels via IoC like
public MainViewModel(UserViewModel user, SearchViewModel search, IEventAggregator events)
{
User = user;
Search = search;
}
but now the design time view doesn't work anymore. A blue squiggly for the d:DataContext.. says, "No parameterless constructor defined for this object".
How can I get it to work?

Answer 1

Well, the principle of IoC (inversion of control) is that dependency solving happens at run time and not at compile time.
As far as I know the designer does not support creating instances of view models with dependencies and solving them for itself. Thus there is the requirement for the empty constructor.
This would be the "hack" I'd use, if you insist on design-time support.
public ShellViewModel() : this(new UserViewModel(), new SearchViewModel())
{
}
public ShellViewModel(UserViewModel user, SearchViewModel search, IEventAggregator events)
{
User = user;
Search = search;
}
But as one can imagine this is going to get ugly while developing a larger application, if the UserViewModel gets dependencies. The new dependencies might have dependencies either, and so on... you see, you just run into the problem that IoC should actually solve.
But I think it is not too bad that your ContentControls remain empty. What you achieve with creating sub view models is decoupling the actual code. Why would you couple it once again in your designer? Because the corresponding views get decoupled through these ContentControls either.
The bigger the view model hierarchy gets, the bigger the content control hierarchy gets, which - in my opinion - blows up the amount of shown items in your designer unnecessarily.

Answer 2

The better solution in this case is to use DesignData instead of DesignInstance. The data needs to be created in Blend, but if you're using VS2012/VS2013 Blend comes with VS.
See these links for tutorials.
http://visitmix.com/labs/rosetta/eyesofblend/datatemplates/
http://msdn.microsoft.com/en-us/magazine/dn169081.aspx
What you want to do is create "sample data from class". This will insert data into a fictive instance of your class, as well as inserting lorem ipsum like text in your strings, several items in your lists etc.
It will keep those nasty empty constructors away, and you dont need to maintain test data in that empty constructor.