Drag & drop using Simple MVVM Toolkit

Aug 28, 2011 at 6:22 PM
Edited Aug 28, 2011 at 6:58 PM

I am trying to get drag & drop functionality in an application using the Simple MVVM Toolkit. The requirements are fairly straight forward – dragging from a ListView onto an ItemsControl and also within the ItemsControl. The adorner is text, so nothing fancy. Are there any particular features of the Simple MVVM Toolkit I should use, such as NotificationEventArgs, DelegateCommand, Blend EventTrigger/Action, etc And how would I pass the necessary parameters using one of these? Or just stick with the built in DoDragDrop handler and events?

Edit: Just wanted to clarify my question a bit further: In a number of other mvvm frameworks I have looked at there is an EventToCommand implementation, can & how does Simple MVVM Toolkit implement this (maybe I missed it in the documentation?). Additionally there is usually a “PassEventArgsToCommand” attribute that can be set to use the event args, does Simple MVVM Toolkit implement this?

 

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mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} --> <!--[endif]-->Just wanted to clarify my question a bit further: In a number of other mvvm frameworks I have looked at there is an EventToCommand implementation, can & how does Simple MVVM Toolkit implement this. Additionally there is usually a “PassEventArgsToCommand” attribute that can be set to use the event args, can & how does Simple MVVM Toolkit implement this?
Coordinator
Aug 29, 2011 at 1:57 PM
Edited Sep 10, 2011 at 9:56 PM
I would treat the drag and drop event like any other event and use a Blend event event trigger with a CallMethodAction to invoke a method on the ViewModel. The method would not accept any parameters and get its data from properties bound to various UI elements. Will that work for you?

Cheers,
Tony
Sent from my iPad
Aug 31, 2011 at 5:54 AM

This approach sounds good but I have come across a couple of problems:


The ItemsControl does not expose a SelectedItem for me to use to set a ViewModel property. In the proof-of-concept versions of the app I have used the MouseButtonEventArgs (e.source) to get the item if the source is the ItemsControl – I use the position of the item to determine which one is selected.


I also use the DragEventArgs to determine if I am displaying the adorner or not.


How would I achieve this kind of functionality without parameters? I may be missing some of the finer points of mvvm and\or simple mvvm toolkit as I am fairly new to mvvm as a design pattern.

 

Coordinator
Sep 10, 2011 at 10:00 PM

I think in the next version of the toolkit I will include an EventToCommand behavior that will allow you to wire up any event to a Command that accepts a parameter.  There are some features like that which folks have asked for but that require some additional work to implement. ;)

In the meantime, as a workaround, I would suggest that in the event handler in the code-behind you call a ViewModel method that accepts parameters and pass the info in.  That should work.

Cheers,

Tony