CODEWITHSUNDEEP
c#wpf
David
David

Reputation: 1293

WPF - Raise Event from UserControl ViewModel

I have a WPF application that uses MVVM

The MainWindowViewModel has references to other ViewModels like so:-

            this.SearchJobVM = new SearchJobViewModel();
            this.JobDetailsVM = new JobDetailsViewModel();
            this.JobEditVM = new JobEditViewModel();

I have a Label on the MainWindow called StatusMessage which is bound to a string property on the MainWindowViewModel

I want to be update to change this message on any of the other view models and have it updated on the UI

Do I need to Raise an Event from the other ViewModels to the MainWindowViewModel?

How do I go about achieving this?

Upvotes: 2

Views: 4011

Answers (2)

Serge Desmedt
Serge Desmedt

Reputation: 138

I think it depends on how much you want the viewmodels to be independent of each other;

The solution of user3690202, allthough viable, does create a dependency of the child viewmodels (SearchJobViewModel, etc...) on the MainViewModel.

And because your viewmodels probably allready implement INotifyPropertyChanged, you could expose the message on the childviewmodels a a property and make the MainViewModel listen for changes on the childviewmodels.

Thus, you would get something like the followin:

class SearchJobViewModel : INotifyPropertyChanged
{
    string theMessageFromSearchJob;
    public string TheMessageFromSearchJob
    {
        get { return theMessageFromSearchJob; }
        set {
            theMessageFromSearchJob = value;           
            /* raise propertychanged here */ }
    }
}

And then in the MainViewModel:

this.SearchJobVM = new SearchJobViewModel();
this.SearchJobVM +=  SearchJobVM_PropertyChanged;

void SearchJobVM_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
    if (e.PropertyName == "TheMessageFromSearchJob")
    { 
        this.StatusMessage = this.SearchJobVM.TheMessageFromSearchJob;
    }
}

Upvotes: 3

user3690202
user3690202

Reputation: 4045

The cleanest way I can think of you doing this (and I do it myself sometimes) is to pass a reference to your MainWindowViewModel into these sub-view-models, i.e.:

        this.SearchJobVM = new SearchJobViewModel(this);
        this.JobDetailsVM = new JobDetailsViewModel(this);
        this.JobEditVM = new JobEditViewModel(this);

Then from one of these sub-view-models, provided you have stored your reference in a property named MainViewModel, you could do something like:

MainViewModel.StatusMessage = "New status";

And if your VMs support INotifyPropertyChanged then everything will automatically update.

Upvotes: 2

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