Pass parameters to RelayCommand in code behind

Question

I know that there are multiple posts with similar titles all over SOF and Google, but please bear with me for a minute.

I am following this article to create a context menu for my gridview: http://www.koaxkoaxkoax.com/ribbit/2010/09/creating-dynamic-menus-in-wpf.html

I create the HierarchicalDataTemplate in UserControl.Resources, I have an empty menu in the resources of the gridview, which I then reference in the actual context menu. The XAML (first part of the gridview) looks like this:

 <DataGrid.Resources> <Views:ViewMenuItemCollection x:Key="Menu"> <Views:ViewMenuItem Text="foo"/> <Views:ViewMenuItem Text="bar"/> </Views:ViewMenuItemCollection> </DataGrid.Resources> <DataGrid.ContextMenu> <ContextMenu ItemsSource="{DynamicResource Menu}"/> </DataGrid.ContextMenu>

In the code behind I use FindResource to get a reference to the menu and create one ViewMenuItem-object that is on the same level as foo and bar. Then I iterate through a list and create one ViewMenuItem-object per list item and attach them as child objects. That looks just as I want to have it. But I can't get the actual functionality to work.

The inner part of the foreach-loop (where I create the child objects) looks like this:

ViewMenuItem seriesItem = new ViewMenuItem(); seriesItem.Text = series.ForcedName; seriesItem.Command = new RelayCommand<Series>(p=>_view.SetSeriesExecute(p)); _setSeriesMenuItem.Children.Add(seriesItem);

Especially the line containing p=>_view.SetSeriesExecute(p) is confusing me. I have found many many examples that look exactly like it. When I run my program and click on one of the child elements, the SetSeriesExecute method is properly called - but the paramter is always null. Not too surprising, because at no point I actually supply an object of type Series as parameter. I have tried to provide the parameter in the RelayCommand constructor like this: p=>_view.SetSeriesExecute(mySeriesObject). It compiles, but SetSeriesExecute is never called.

My goal is very simple (at least I think it is): When the program reacts to a click on an element in the context menu, the method (SetSeriesExecute) needs to know which item has actually been selected (=clicked on) by the user. Unfortunately I was not able to figure out where and how I can supply the parameters to SetSeriesExecute, despite 4 hours of serious research. And the fact that everyone else seems to understand the available examples doesn't make me feel particularly good about myself and I offer lifelong gratitude for every hint.

Best Peter

Khan · Accepted Answer · 2013-02-20 17:59:33Z

1

What you're missing is the CommandParameter.

Try setting seriesItem.CommandParameter to whatever you would like to pass to the SetSeriesExecute method. p in p=>_view.SetSeriesExecute(mySeriesObject) will be that parameter.

answered Feb 20, 2013 at 17:59

Khan

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7 Comments

user7116 Over a year ago

+1, or apply a binding to the CommandParameter. In fact, both should be bound.

Peter Over a year ago

I have added Series CommandParameter to my ViewMenuItem-class. But the parameter in SetSeriesExecute is still null. How would SetSeriesExecute know to look for this Property anyway?

Khan Over a year ago

What is series.ForcedName ?

Peter Over a year ago

ForcedName is a string property and is used as the text of the menu item

Khan Over a year ago

I thought text is set here: <Views:ViewMenuItem Text="foo"/>

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