CODEWITHSUNDEEP
wpfmvvm
Adrian
Adrian

Reputation: 769

Retrieving value of a label in which is binded to an element value

In my current scenario (WPF, MVVM), I have a user control which hosts a visio diagram. This user control is located on a view, next to a number of labels and a datagrid element.

The user control contains a DependencyProperty object SelectedNode which value is updated with the information received from the Visio diagram. The labels' content are binded so that they display the information contained in the SelectedNode (e.g. id, name):

<Label Grid.Row="1" Grid.Column="1" x:Name="lbNodeIdValue" HorizontalAlignment="Left"
                                           Content="{Binding ElementName=visioControlUC, Path=SelectedNode.Id, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}"/>

Every time I change the selection in the diagram, the label's content changes as expected.

Next to this label, I would like to display a datagrid containing information based on the id displayed in the label. This is where I ran into problems, as I can't seem to be able to get the value of the Content property of the label in the viewmodel class.

I have tried using the MultiBinding property on the Content element of the label, and creating a second binding with Mode=OneWayToSource to set the value of the label's Content to a property I have defined in the viewmodel class.

What would be a proper way to retrieve this value in my viewmodel class?

Thanks, Adrian

Upvotes: 0

Views: 89

Answers (1)

Rachel
Rachel

Reputation: 132548

Ideally your Datagrid's ViewModel should get the value of the selected label from the other ViewModel. You should not rely on Views to transfer application data between ViewModels.

It sounds like the SelectedNode value originates from the UserControl, and not the ViewModel, so you'll need to bind the UserControl.SelectedNodeId to a ViewModel somewhere so the ViewModels have access to this data

<local:myUserControl x:Name="visioControlUC" 
                     SelectedNode="{Binding SelectedNodeId}" />

If the value is needed by more than one ViewModel, I would highly recommend some kind of event system, such as MVVM Light's Messenger or Prism's EventAggregator. This would allow your ViewModels to subscribe to something like a SelectedNodeChangedEventMessage, and the ViewModel which actually contains the SelectedNodeId can broadcast that message anytime the value changes. You can find an example of both on my blog post about Communication between ViewModels.

Upvotes: 1

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