如何使用 ICommand 将 combobox 事件绑定到视图模型

Question

I am relatively new to MVVM and I want to bind my view to the view model. I have a lot of code to move from the CodeBehind into the ViewModel class.

What I would like to do is binding the ComboBox Events to the corresponding ViewModel ICommand methods. I want the ComboBox to show "CompanyB" when the view loads and when I make a selection, the ComboBox should give me "CompanyA", "CompanyB" and "CompanyC" as options to select from.

After a company was selected, the values of the 2 textboxes below

Nachbest.Empf_Ansprechpartner

Nachbest.Empfaenger_Mail

must change accordingly.

The problem is with my code both the ComboBox and the textboxes remain empty and there is also nothing to choose from inside the combobox.

Could you please help me find what I am missing here? Thanks in advance for any help!

XAML (neueNachbestellung.xaml):

<Window xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity">
    <Grid>
        <StackPanel Grid.Column="0" Margin="25,25,0,0" x:Name="leftStPnl">
            <ComboBox x:Name="cboxEmpfaenger" 
                      ItemsSource="{Binding Empf}" 
                      Text="{Binding Empfaenger}" 
                      FontSize="12" Width="150" Margin="118,0,0,0"                      
                      SelectedItem="{Binding SelValue}">
            </ComboBox>
            <TextBox x:Name="txtEmpfAnsprechpartner" Text="{Binding Empf_Ansprechpartner}" FontSize="12" IsEnabled="False" Width="150" Margin="50,0,0,0"/>    
            <TextBox x:Name="txtEmpfMail" Text="{Binding Empfaenger_Mail}" FontSize="12" IsEnabled="False" Width="150" Margin="73,0,0,0"/>
        </StackPanel>
    </Grid>
</Window>

Code Behind (neueNachbestellung.xaml.cs):

public neueNachbestellung(string someId) 
{
    InitializeComponent();
    this.DataContext = new neueNachbestellungViewModel(someId);
}

View Model(neueNachbestellungViewModel.cs) :

public class neueNachbestellungViewModel: INotifyPropertyChanged
{
public ICommand LoadCombobox => new DelegateCommand<object>(ExecuteLoadCombobox);
public ICommand ComboboxSelectionChanged => new DelegateCommand<object>(ExecuteComboboxSelectionChanged);
public Nachbestellung Nachbest { get; set; }
private object someObject;
private ObservableCollection<string> _empf;
        public ObservableCollection<string> Empf
        {
            get { return _empf; }
            set
            {
                _empf = value;
                OnPropertyChanged("Empf");
            }
        }
        private string _selValue = "12";
        public string SelValue  
        {
            get { return _selValue; }
            set
            {
                _selValue = value;
                OnPropertyChanged("SelValue");
            }
        }

 public event PropertyChangedEventHandler PropertyChanged;
        public virtual void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

public neueNachbestellungViewModel(string id)
{

    this.Artikel = new ArtikelViewModel();
    this.ArtikelList = new ObservableCollection<Artikel>();
    InitializeReorderModel(id);    
    ExecuteComboboxSelectionChanged(someObject);                        
}

public void InitializeReorderModel(string id)
{
    //set the MODEL
    this.Nachbest = new Nachbestellung();

    //Retrieve and set some values on *VIEW LOAD*!
    var dbOracle = new Datenbank();
    this.Nachbest.Bv = dbOracle.GetBauvorhaben(hv);
    this.Nachbest.Hv = hv;
    this.Nachbest.Bauleiter = dbOracle.GetBauleiter(hv);
    this.Nachbest.Projektleiter = dbOracle.GetProjektleiter(hv);
}

private void ExecuteLoadCombobox(object param)
{
    Empf = new ObservableCollection<string>()
    {
        "CompanyA",
        "CompanyB",
        "CompanyC"         
    };

    //Company B is the standard selection on combobox load                     
    Nachbest.Empf_Ansprechpartner = "CompanyB";
    Nachbest.Empfaenger_Mail = "orders@companyB.com";
}

private void ExecuteComboboxSelectionChanged(object param)
{
    Empf = new ObservableCollection<string>()
    {
        "CompanyA",
        "CompanyB",
        "CompanyC"             
    };

    switch (SelValue)
    {

        case "CompanyA":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyA";
                Nachbest.Empfaenger_Mail = "service@companyA.com";
            }
            break;

        case "CompanyB":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyB";
                Nachbest.Empfaenger_Mail = "orders@companyB.com";
            }
            break;

        case "CompanyC":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyC";
                Nachbest.Empfaenger_Mail = "info@companyC.com";
            }
            break;

        default:
            MessageBox.Show("Something went wrong with the company selection!");
            break;
    }
}
}

View Fragment :

Answer 1

This is my quick & dirty solution. It does what it needs to and I don't have these click_button, selection_changed events inside my code behind anymore but inside my view model. That is all I need for now. Obviously not an elegant solution but it is working. I hope I can help some developers with it in the future who run into similar problems. Just a side note: The ICommand properties inside the view model are not necessary in this scenario but I am using them to handle button click events in the view. You can replace them with your own properties if you don't need the DelegateCommand class in your application.

XAML (neueNachbestellung.xaml):

<Window>
    <Grid>
        <StackPanel Grid.Column="0" Margin="25,25,0,0" x:Name="leftStPnl">
            <ComboBox x:Name="cboxEmpfaenger" 
                      ItemsSource="{Binding Empf}" 
                      Text="{Binding Empfaenger}" 
                      FontSize="12" Width="150" Margin="118,0,0,0"                      
                      SelectedItem="{Binding SelValue}">
            </ComboBox>
            <TextBox x:Name="txtEmpfAnsprechpartner" DataContext="{Binding Nachbest}" Text="{Binding Empf_Ansprechpartner}" FontSize="12" IsEnabled="False" Width="150" Margin="50,0,0,0"/>    
            <TextBox x:Name="txtEmpfMail" DataContext="{Binding Nachbest}" Text="{Binding Empfaenger_Mail}" FontSize="12" IsEnabled="False" Width="150" Margin="73,0,0,0"/>
        </StackPanel>
    </Grid>
</Window>

Code Behind (neueNachbestellung.xaml.cs):

public neueNachbestellung(string someId) 
{
    InitializeComponent();
    this.DataContext = new neueNachbestellungViewModel(someId);
}

neueNachbestellungViewModel.cs:

public class neueNachbestellungViewModel: INotifyPropertyChanged
{
//public ICommand LoadCombobox => new DelegateCommand<object>(ExecuteLoadCombobox);
public ICommand ComboboxSelectionChanged => new DelegateCommand<object>(ExecuteComboboxSelectionChanged);
public Nachbestellung Nachbest { get; set; }
private object someObject; //DelegateCommand.cs requires an argument
private ObservableCollection<string> _empf;
        public ObservableCollection<string> Empf
        {
            get { return _empf; }
            set
            {
                _empf = value;
                OnPropertyChanged("Empf");
            }
        }
        private string _selValue = "CompanyB"; //default value
        public string SelValue  
        {
            get { return _selValue; }
            set
            {
                _selValue = value;
                OnPropertyChanged("SelValue");
 switch (SelValue)
    {

        case "CompanyA":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyA";
                Nachbest.Empfaenger_Mail = "service@companyA.com";
            }
            break;

        case "CompanyB":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyB";
                Nachbest.Empfaenger_Mail = "orders@companyB.com";
            }
            break;

        case "CompanyC":
            {
                Nachbest.Empf_Ansprechpartner = "CompanyC";
                Nachbest.Empfaenger_Mail = "info@companyC.com";
            }
            break;

        default:
            MessageBox.Show("Something went wrong with the company selection!");
            break;
    }
//setting the Empfaenger property here with the current selected value is necessary for the database insert later on!
Nachbest.Empfaenger = SelValue;
            }
        }

 public event PropertyChangedEventHandler PropertyChanged;
        public virtual void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

public neueNachbestellungViewModel(string id)
{

    this.Artikel = new ArtikelViewModel();
    this.ArtikelList = new ObservableCollection<Artikel>();
    InitializeReorderModel(id);    
    ExecuteComboboxSelectionChanged(someObject);                        
}

public void InitializeReorderModel(string id)
{
    //set the MODEL
    this.Nachbest = new Nachbestellung();

    //Retrieve and set some values on *VIEW LOAD*!
    var dbOracle = new Datenbank();
    this.Nachbest.Bv = dbOracle.GetBauvorhaben(hv);
    this.Nachbest.Hv = hv;
    this.Nachbest.Bauleiter = dbOracle.GetBauleiter(hv);
    this.Nachbest.Projektleiter = dbOracle.GetProjektleiter(hv);
}

private void ExecuteComboboxSelectionChanged(object param)
{
    Empf = new ObservableCollection<string>()
    {
        "CompanyA",
        "CompanyB",
        "CompanyC"             
    };
Nachbest.Empf_Ansprechpartner = "CompanyB";
            Nachbest.Empfaenger_Mail = "orders@companyB.com";
            Nachbest.Empfaenger = SelValue; //if this is left out and there is no selection (just the default remaining unchanged!), Nachbest.Empfaenger will be null!
}
}