How to set an item as selected in a combobox - wpf

Question

It seems nobody has yet found a way to set the comboboxitem as selected with a SelectedItem="Binding Property".
Is the solution to use a IsSelected Property in the ViewModel object within the combobox itemssource?

Answer 1

Our successful approach for binding a combobox is the following...
<ComboBox
ItemsSource="{Binding Path=AllItems}"
SelectedItem="{Binding Path=CurrentItem, Mode=TwoWay}" />
<TextBlock Text="{Binding Path=CurrentItem, Mode=TwoWay}" />
class public ItemListViewModel
{
public ObservableCollection<Item> AllItems {get; set;}
private Item _currentItem;
public Item CurrentItem
{
get { return _currentItem; }
set
{
if (_currentItem == value) return;
_currentItem = value;
RaisePropertyChanged("CurrentItem");
}
}
}

Answer 2

Not sure why you can't data bind to SelectedItem on a ComboBox without seeing your code. Below shows you how to do it using a CollectionView which has current item management built in which comboboxes supports. CollectionView has a CurrentItem get property you can use to get currently selected.
XAML:
<Window x:Class="CBTest.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel>
<ComboBox
ItemsSource="{Binding Path=Names}"
IsSynchronizedWithCurrentItem="True">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
<TextBlock Text="{Binding Path=Names.CurrentItem}" />
</StackPanel>
</Window>
Code behind:
using System.Collections.Generic;
using System.Windows;
using System.Windows.Data;
namespace CBTest
{
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
DataContext = new VM();
}
}
public class VM
{
public VM()
{
_namesModel.Add("Bob");
_namesModel.Add("Joe");
_namesModel.Add("Sally");
_namesModel.Add("Lucy");
Names = new CollectionView(_namesModel);
// Set currently selected item to Sally.
Names.MoveCurrentTo("Sally");
}
public CollectionView Names { get; private set; }
private List<string> _namesModel = new List<string>();
}
}

Answer 3

what i found is that in combobox soure code, selecteditem is set by using list selectedindex
combobox using
public object SelectedItem {
get {
int index = SelectedIndex;
return (index == -1) ? null : Items[index];
}
set {
int x = -1;
if (itemsCollection != null) {
//bug (82115)
if (value != null)
x = itemsCollection.IndexOf(value);
else
SelectedIndex = -1;
}
if (x != -1) {
SelectedIndex = x;
}
}
}
this method always return -1 or null every time you set Selecteditem by code
x = itemsCollection.IndexOf(value);
its reported as bug (82115) in combobox code
so the working method is to use SelectedIndex directly and bind to it instead of SelectemItem property and if you want you can read only the item from binding to the SelectedItem property or obtain it in your code using ItemsSource itself.
This working for me fine.