how to parametrize an import in a View?
I am loo开发者_如何学Pythonking for some help and I hope that some good soul out there will be able to give me a hint :)
I am building a new application by using MVVM Light. In this application, when a View is created, it instantiates the corresponding ViewModel by using the MEF import.
Here is some code:
public partial class ContractEditorView : Window
{
public ContractEditorView ()
{
InitializeComponent();
CompositionInitializer.SatisfyImports(this);
}
[Import(ViewModelTypes.ContractEditorViewModel)]
public object ViewModel
{
set
{
DataContext = value;
}
}
}
And here is the export for the ViewModel:
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(ViewModelTypes.ContractEditorViewModel)]
public class ContractEditorViewModel: ViewModelBase
{
public ContractEditorViewModel()
{
_contract = new Models.Contract();
}
}
Now, this works if I want to open a new window in order to create a new contract... or in other words, it is perfect if I don't need to pass the ID of an existing contract.
However let's suppose I want to use the same View in order to edit an existing contract. In this case I would add a new constructor to the same View, which accepts either a model ID or a model object.
"Unfortunately" the ViewModel is created always in the same way:
[Import(ViewModelTypes.ContractEditorViewModel)]
public object ViewModel
{
set
{
DataContext = value;
}
}
As far as I know, this invokes the standard/no-parameters constructor of the corresponding ViewModel at composition-time.
So what I would like to know is how to differentiate this behavior? How can I call a specific constructor during composition time? Or how can I pass some parameters during the Import?
I really apologize if this question sounds silly, but I have only recently started to use MEF!
Thanks in advance,
Cheers, Gianluca.
You CAN do this. Check out the Messenger implementation in MVVM-Light. You can pass a NotificationMessage(Of Integer) to send the right ID to the view model. The view model has to register for that type of message, and load it when a message is sent.
MEF Imports by default only have a parameterless constructor.
精彩评论