How to programmatically set SelectedItem of a data-bound WPF ComboBox?

Question

Question: Can anyone please provide a full code example that shows how one does programmatically change the SelectedItem of a data-bound WPF ComboBox?

Code sample: Here is what I currently have.

 

<Window x:Class="Wpf.ComboBoxDemo.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>
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <ComboBox Name="MyComboBox" DisplayMemberPath="LastName" SelectedIndex="0"/>
  </Grid>
</Window>

 

using System.Collections.ObjectModel;
using System.Windows;

namespace Wpf.ComboBoxDemo
{
  public partial class MainWindow : Window
  {
    public MainWindow()
    {
      InitializeComponent();

      ObservableCollection<Person> myPersonList = new ObservableCollection<Person>();

      Person personJobs = new Person("Steve", "Jobs");
      Person personGates = new Person("Bill", "Gates");

      myPersonList.Add(personJobs);
      myPersonList.Add(personGates);

      MyComboBox.ItemsSource = myPersonList;

      // How do I programmatically select the second Person, i.e. "Gates"?
      // The best pratice must be to somehow to set something like IsCurrentlySelected on the model, so the view update automatically. But how?
      MyComboBox.SelectedIndex = 1; // This works, but is there no way without using the index?

    }

    private class Person
    {
      public string FirstName { get; set; }
      public string LastName { get; set; }

      public Person(string firstName, string lastName)
      {
        FirstName = firstName;
        LastName = lastName;
      }
    }
  }
}

 

Similar questions: I have of course searched the Internet first, but found nothing that helped me.

• Changing the SelectedItem of a enum-bound combobox inside ViewModel (MSDN )
• Programmatically set ComboBox SelectedItem in WPF (3.5sp1) (Stack Overflow )

Answer 1

I'm not sure, I fully understand your question.  Are you wanting to set the default item in your list programattically?  Here is how I populate a combo box from a SQL Database, and the default selected item is set with this line: "btnServer.SelectedIndex = 3;"

    private void SetUpbtnServer()
    {
      DataTable dt = bl.GetServerNames();
      btnServer.DataContext = dt.DefaultView;
      Binding bind = new Binding();
      Binding tip = new Binding(dt.Columns["ToolTip"].ToString());
      btnServer.SelectedIndex = 3;
      btnServer.IsSynchronizedWithCurrentItem = true;
      btnServer.Text = "Database Server";
      btnServer.ToolTip = "Select the new DB Server.";
      btnServer.IsTextSearchEnabled = false;
      btnServer.VerticalAlignment = VerticalAlignment.Top;
      btnServer.HorizontalAlignment = HorizontalAlignment.Left;
      btnServer.HorizontalContentAlignment = HorizontalAlignment.Left;
      btnServer.DisplayMemberPath = dt.Columns["ServerName"].ToString();
      btnServer.SetBinding(ComboBoxItem.ToolTipProperty, tip);
      btnServer.SetBinding(ComboBox.ItemsSourceProperty, bind);
    }

Answer 2

SelectedIndex is working for me, too. But SelectedItem = personGates is not working and I don't know why.

I would prefer the SelectedItem approach because otherwise I have to do the following which is rather procedural code, instead of declarative WPF code.

1. Find out what person is currently selected in my data model.
2. Take the person object and iterate over the items of the combobox to find out its index.
3. Set myCombobox.SelectedIndex = indexOfPerson.

Does that clarify my initial question?

Answer 3

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Collections.ObjectModel;

namespace WpfApplication2
{
  /// <summary>
  /// Interaction logic for Window1.xaml
  /// </summary>
  public partial class Window1 : Window
  {
    public Window1()
    {
      InitializeComponent();
      ObservableCollection<Person> myPersonList = new ObservableCollection<Person>();



      Person personJobs = new Person("Steve", "Jobs");

      Person personGates = new Person("Bill", "Gates");



      myPersonList.Add(personJobs);

      myPersonList.Add(personGates);

      MyComboBox.ItemsSource = myPersonList;

      MyComboBox.SelectedItem = personGates;
    }
  }


  public class Person
  {

    public string FirstName { get; set; }

    public string LastName { get; set; }



    public Person(string firstName, string lastName)
    {

      FirstName = firstName;

      LastName = lastName;

    }

  }

}

This code works fine for me:

 

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Answer 4

Darn... now it's working here too. *puzzled*

Thank you very much for verifying it!

Answer 5

Eg: when binding to a list to a combobox.  In the code-behind you need one line:

  combobox.ItemsSource = IList;

and in the xamle you need one line:

<ComboBox Name="Mycombobox" SelectedValue="{Binding Path="This object(int,string,whatever you want) will hold the selected value you specify in the selectedvaluepath property of the combobox", Mode=TwoWay} SelectedValuePath="the ITEM property you want to output from selectedValue" DisplayMemberPath="Name" />

This is the shortest way!