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POView and View-Model in WPF
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copied!<p>I've been messing around with MVVM in WPF and have a quick question for folks. Right now I have:</p> <ul> <li>MainWindow which consists of a MenuBar and a UserControl </li> <li>UserControl (mentioned above) contains basically a Grid.</li> </ul> <p>I expose access to Grid Properties as I need in the UserControl, but the User Control knows nothing nor interacts with the MainWindow.</p> <p>I also have a class I call ViewModel which does manipulation of the MainWindow/UserControl for me. My understanding is that the ViewModel knows about the View (MainWindow/UserControl) and how to manipulate it while the View generally knows nothing about the ViewModel.</p> <p>If I have that right, here is my question:</p> <ol> <li><p>When I do button clicks on the MainWindow MenuBar I want to perform actions. Right now those actions are bound to say a EventHandler in the MainWindow and the EventHandler instantiates the ViewModel and calls the method for handling like such:</p> <pre><code>private void RunQueryMenuItemAdvClick(object pSender, RoutedEventArgs pRoutedEventArgs) { ViewModel vViewModel = new ViewModel(this); vViewModel.RunQuery(); } </code></pre></li> </ol> <p>The View Model looks something like this:</p> <pre><code> public class ViewModel { private DataProvider fDataProvider; private MainWindow fMainWindow; private BackgroundWorker fQueryWorker = new BackgroundWorker(); public ViewModel(MainWindow pMainWindow) { fDataProvider = new DataProvider(); fMainWindow = pMainWindow; //Query Worker fQueryWorker.DoWork += QueryWorkerDoWork; fQueryWorker.RunWorkerCompleted += QueryWorkerCompleted; } private void QueryWorkerCompleted(object pSender, RunWorkerCompletedEventArgs pRunWorkerCompletedEventArgs) { fMainWindow.UserControl_Data.busyIndicator1.IsBusy = false; fMainWindow.UserControl_Data.DataToPresent = pRunWorkerCompletedEventArgs.Result; } private void QueryWorkerDoWork(object pSender, DoWorkEventArgs pDoWorkEventArgs) { pDoWorkEventArgs.Result = this.fDataProvider.GetParticipantsData(); } public void RunQuery() { if (!fQueryWorker.IsBusy) { fMainWindow.UserControl_Data.busyIndicator1.IsBusy = true; fQueryWorker.RunWorkerAsync(); } } } </code></pre> <p>Am I way off base with my approach here?</p> <p><em><strong>EDIT New Solution:</em></strong> First, thanks to everyone for their response. I'd like to provide my new solution. This may not be 100% MVVM, but it has to be at least 80% better than what I had!</p> <p>My ViewModel:</p> <pre><code> public class ViewModel : ObservableObject { private DataProvider fDataProvider; private BackgroundWorker fQueryWorker = new BackgroundWorker(); public ViewModel() { fDataProvider = new DataProvider(); //Query Worker fQueryWorker.DoWork += QueryWorkerDoWork; fQueryWorker.RunWorkerCompleted += QueryWorkerCompleted; } //This is my Command for the MainWindow.MenuItem to bind to to run a query RelayCommand fRunQueryCommand; public ICommand RunQueryCommand { get { if (this.fRunQueryCommand == null) { this.fRunQueryCommand = new RelayCommand(param => this.RunQuery(), param => true); } return this.fRunQueryCommand; } } //This is my Property for the UserControl.progressBar to bind to private bool fIsBusy; public bool IsBusy { get { return this.fIsBusy; } set { if (value != this.fIsBusy) { this.fIsBusy = value; OnPropertyChanged("IsBusy"); } } } //This is my Property for the UserControl.gridControl.ItemSource to bind to private object fSource; public object Source { get { return this.fSource; } set { if (value != this.fSource) { this.fSource = value; OnPropertyChanged("Source"); } } } private void QueryWorkerCompleted(object pSender, RunWorkerCompletedEventArgs pRunWorkerCompletedEventArgs) { this.IsBusy = false; Source = pRunWorkerCompletedEventArgs.Result; } private void QueryWorkerDoWork(object pSender, DoWorkEventArgs pDoWorkEventArgs) { pDoWorkEventArgs.Result = this.fDataProvider.GetParticipantsData(); } public void RunQuery() { if (!fQueryWorker.IsBusy) { this.IsBusy = true; fQueryWorker.RunWorkerAsync(); } } </code></pre> <p>I've removed all of my code from behind the MainWindow and the UserControl and replaced it with XAML for Binding the elements that I needed to the two properties in ViewModel and the 1 Command. Feel free to provide additional feedback on what I may or may not have picked up on with the re-factoring. (Aside from the lack of a Model usage).</p>

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