SelectedItem on ComboBox

Question

There is a ComboBox in the application which is bound to a collection of items. There are cases that user can select an item from the ComboBox but the selected item might not be ready yet so the ComboBox selected item must get back to the previous selected item (or some other item in the collection), but in the current application ComboBox always shows the selected item from the user instead of retrieving the valid item after setting it back and calling notify property change.

The flowing is a simplified code of which shows the problem.

public partial class MainWindow : Window, INotifyPropertyChanged
{
    private List<Customer> _Customers = new List<Customer>();

    public List<string> CustomerNames
    {
        get
        {
            var list = new List<string>();
            foreach (var c in _Customers)
            {
                list.Add(c.Name);
            }
            return list; ;
        }
    }

    public string CustomerName
    {
        get
        {
            var customer = _Customers.Where(c => c.IsReady).FirstOrDefault();
            return customer.Name;
        }
        set
        {
            NotifyPropertyChanged("CustomerName");
        }
    }

    public MainWindow()
    {
        SetupCustomers();
        InitializeComponent();
        this.DataContext = this;
    }

    private void SetupCustomers()
    {
        _Customers.Add(new Customer("c1", true));
        _Customers.Add(new Customer("c2", false));
        _Customers.Add(new Customer("c3", false));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Customer
{
    public Customer(string name, bool isReady)
    {
        this.Name = name;
        this.IsReady = isReady;
    }

    public bool IsReady { get; set; }

    public string Name { get; set; }

    public override bool Equals(object obj)
    {
        return base.Equals(obj);
    }
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
}    


<Window x:Class="TryComboboxReset.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid>

    <ComboBox   Width="100"
                Height="25"
                ItemsSource="{Binding Path=CustomerNames, Mode=OneWay}"
                SelectedItem="{Binding Path=CustomerName, Mode=TwoWay}"/>

</Grid>

score 1 · Accepted Answer · answered Jun 14 '13 at 16:32

The problem was UI thread, I used dispatcher to fix this problem

 public partial class MainWindow : Window, INotifyPropertyChanged
{
    private ObservableCollection<Customer> _Customers =
        new ObservableCollection<Customer>();

    public ObservableCollection<Customer> CustomerNames
    {
        get
        {
            return _Customers;
        }
    }

    public Customer CustomerName
    {
        get
        {
            return _Customers.Where(c => c.IsReady == true).FirstOrDefault();
        }
        set
        {
            // Delay the revert
            Application.Current.Dispatcher.BeginInvoke(
                new Action(() => NotifyPropertyChanged("CustomerName")), DispatcherPriority.ContextIdle, null);
        }
    }

    public MainWindow()
    {
        SetupCustomers();
        InitializeComponent();
        this.DataContext = this;
    }

    private void SetupCustomers()
    {
        _Customers.Add(new Customer("c1", true));
        _Customers.Add(new Customer("c2", false));
        _Customers.Add(new Customer("c3", false));
        CustomerName = _Customers.Where(c => c.IsReady == true).FirstOrDefault();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Customer
{
    public Customer(string name, bool isReady)
    {
        this.Name = name;
        this.IsReady = isReady;
    }

    public bool IsReady { get; set; }

    public string Name { get; set; }
}   

<ComboBox   Width="400"
            Height="25"
            ItemsSource="{Binding Path=CustomerNames}"
            SelectedValue="{Binding CustomerName,Mode=TwoWay}"    >
       <ComboBox.ItemTemplate>
             <DataTemplate>
                 <TextBlock Text="{Binding Name}"/>
             </DataTemplate>
        </ComboBox.ItemTemplate>
 </ComboBox>

score 0 · Answer 2 · answered Jun 13 '13 at 01:56

You aren't actually setting the value of the selected customer name in your setter, and your getter is always going to return the first "ready" customer name it finds...

If I'm understanding the problem correctly, you need to be doing something more along these lines:

private string _customerName = null;

public string CustomerName
    {
        get
        {
            if(_customerName == null) 
            {
                _customerName = _Customers.Where(c => c.IsReady).FirstOrDefault().Name;
            }
            return _customerName;
        }
        set
        {
            _customerName = value;
            NotifyPropertyChanged("CustomerName");
        }
    }

That was intentional as I mentioned in the question when customer is not ready it should not be set, for example in this example when user chooses the “C2” from combobox the setter will set the selected customer must back to the “C1” (in this example only “C1” is ready which was intentional to make the code easier to read) but when I run the application even though the setter picks the “C1” and getter returns it but Combobox shows the “C2” as the selected item. — Fred Jand, Jun 13 '13 at 13:43

SelectedItem on ComboBox

2 Answers2

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