Binding ComboBox SelectedItem using MVVM

Question

I have a problem with the SelectedItem in my ComboBox     lt ComboBox Name  cbxSalesPeriods          ItemsSource   Binding SalesPeriods           DisplayMemberPath  displayPeriod          SelectedItem   Binding SelectedSalesPeriod           SelectedValuePath  displayPeriod          IsSynchronizedWithCurrentItem  True   gt     If I open the ComboBox  I see the values    If I select an item  the selected Item won t be shown   Has anybody an idea   In my ViewModel I have these two properties   public ObservableCollection lt SalesPeriodVM gt  SalesPeriods   get  private set     private SalesPeriodVM selectedSalesPeriod  public SalesPeriodVM SelectedSalesPeriod       get   return selectedSalesPeriod         set                if  selectedSalesPeriod    value                        selectedSalesPeriod   value              RaisePropertyChanged  SelectedSalesPeriod                        These are a few properties from the class    public SalesPeriodVO Vo       get   return period       public int Year       get   return period Year        set               if  period Year    value                        period Year   value              RaisePropertyChanged  Year                       public int Month       get   return period Month        set               if  period Month    value                        period Month   value              RaisePropertyChanged  Month                       public string displayPeriod        get               return this ToString             public override string ToString         return String Format   0 D2   1    Month  Year         EDIT  The Following happens If I remove the Property DisplayMemberPath

User · Accepted Answer

You seem to be unnecessarily setting properties on your ComboBox. You can remove the DisplayMemberPath and SelectedValuePath properties which have different uses. It might be an idea for you to take a look at the Difference between SelectedItem, SelectedValue and SelectedValuePath post here for an explanation of these properties. Try this:

<ComboBox Name="cbxSalesPeriods"
    ItemsSource="{Binding SalesPeriods}"
    SelectedItem="{Binding SelectedSalesPeriod}"
    IsSynchronizedWithCurrentItem="True"/>

Furthermore, it is pointless using your displayPeriod property, as the WPF Framework would call the ToString method automatically for objects that it needs to display that don't have a DataTemplate set up for them explicitly.

UPDATE >>>

As I can't see all of your code, I cannot tell you what you are doing wrong. Instead, all I can do is to provide you with a complete working example of how to achieve what you want. I've removed the pointless displayPeriod property and also your SalesPeriodVO property from your class as I know nothing about it... maybe that is the cause of your problem??. Try this:

public class SalesPeriodV
{
    private int month, year;

    public int Year
    {
        get { return year; }
        set
        {
            if (year != value)
            {
                year = value;
                NotifyPropertyChanged("Year");
            }
        }
    }

    public int Month
    {
        get { return month; }
        set
        {
            if (month != value)
            {
                month = value;
                NotifyPropertyChanged("Month");
            }
        }
    }

    public override string ToString()
    {
        return String.Format("{0:D2}.{1}", Month, Year);
    }

    public virtual event PropertyChangedEventHandler PropertyChanged;
    protected virtual void NotifyPropertyChanged(params string[] propertyNames)
    {
        if (PropertyChanged != null)
        {
            foreach (string propertyName in propertyNames) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            PropertyChanged(this, new PropertyChangedEventArgs("HasError"));
        }
    }
}

Then I added two properties into the view model:

private ObservableCollection<SalesPeriodV> salesPeriods = new ObservableCollection<SalesPeriodV>();
public ObservableCollection<SalesPeriodV> SalesPeriods
{
    get { return salesPeriods; }
    set { salesPeriods = value; NotifyPropertyChanged("SalesPeriods"); }
}
private SalesPeriodV selectedItem = new SalesPeriodV();
public SalesPeriodV SelectedItem
{
    get { return selectedItem; }
    set { selectedItem = value; NotifyPropertyChanged("SelectedItem"); }
}

Then initialised the collection with your values:

SalesPeriods.Add(new SalesPeriodV() { Month = 3, Year = 2013 } );
SalesPeriods.Add(new SalesPeriodV() { Month = 4, Year = 2013 } );

And then data bound only these two properties to a ComboBox:

<ComboBox ItemsSource="{Binding SalesPeriods}" SelectedItem="{Binding SelectedItem}" />

That's it... that's all you need for a perfectly working example. You should see that the display of the items comes from the ToString method without your displayPeriod property. Hopefully, you can work out your mistakes from this code example.

User · Answer

I had a similar problem where the SelectedItem-binding did not update when I selected something in the combobox  My problem was that I had to set UpdateSourceTrigger PropertyChanged for the binding    lt ComboBox ItemsSource   Binding SalesPeriods              SelectedItem   Binding SelectedItem  UpdateSourceTrigger PropertyChanged     gt

User · Answer

lt  -- xaml code-- gt       lt Grid gt           lt ComboBox Name  cmbData     SelectedItem   Binding SelectedstudentInfo  Mode OneWayToSource   HorizontalAlignment  Left  Margin  225 150 0 0  VerticalAlignment  Top  Width  120  DisplayMemberPath  name  SelectedValuePath  id  SelectedIndex  0    gt           lt Button VerticalAlignment  Center  Margin  0 0 150 0  Height  40  Width  70  Click  Button Click  gt OK lt  Button gt       lt  Grid gt               student Class         public class Student                       public  int Id   set  get                public string name   set  get                         set 2 properties in MainWindow xaml cs Class         public ObservableCollection lt Student gt  studentInfo   set  get            public Student SelectedstudentInfo   set  get               MainWindow xaml cs Constructor         public MainWindow                         InitializeComponent                bindCombo                this DataContext   this              cmbData ItemsSource   studentInfo                        method to bind cobobox or you can fetch data from database in MainWindow xaml cs         public void bindCombo                         ObservableCollection lt Student gt  studentList   new ObservableCollection lt Student gt                 studentList Add new Student   Id 0  name    Select                   studentList Add new Student   Id   1  name    zoyeb                  studentList Add new Student   Id   2  name    siddiq                  studentList Add new Student   Id   3  name    James                     studentInfo studentList                        button click to get selected student MainWindow xaml cs         private void Button Click object sender  RoutedEventArgs e                        Student student   SelectedstudentInfo              if student Id   0                                MessageBox Show  select name from dropdown                              else                               MessageBox Show  Name    student name    Id    student Id

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