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How do I populate a ComboBox from XAML code behind page?

Posted on 2010-08-16
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Last Modified: 2013-12-17
I am new to Silverlight, so I'll apologize up front for the simple question.  How in the world do you populate the items in a ComboBox from the C# code behind page?  I have always been able to do "combobox.items.add(item);" without a problem.  But now that I am trying to start using Silverlight, it's not working.  I am getting a Null reference exception at line 32 of the code below.  All of the documentation I have read says that this should work.  I'm at a loss.  Please help.

Details:
.net 4.0
VS2010
Silverlight 4.0

Thanks in advance!
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Configuration;
using SilverlightApplication.ServiceReference1;

namespace SilverlightApplication
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            Service1SoapClient wRef = new Service1SoapClient();
            wRef.GetSiteListCompleted += new EventHandler<GetSiteListCompletedEventArgs>(wRef_GetSiteListCompleted);
            wRef.GetSiteListAsync();
        }

        void wRef_GetSiteListCompleted(object sender, GetSiteListCompletedEventArgs e)
        {

            Site[] siteList = e.Result.ToArray();
            foreach (Site site in siteList)
            {
                comboBox1.Items.Add(site.SiteCode.ToString());
            }
        }



    }
}

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Question by:ged125
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9 Comments
 
LVL 30

Expert Comment

by:Reza Rad
ID: 33451491
Why you don't set DataContext property of combo box? like this:
comboBox1.DataContext=something;


also you need to set SelectedValuePath and DisplayMemberPath in xaml, like this:

<ComboBox Name="comboBox1" Width="150" SelectedValuePath="ID" DisplayMemberPath="Name" ></ComboBox>


0
 
LVL 6

Author Comment

by:ged125
ID: 33451497
Can you give me a complete example including the code behind??
0
 
LVL 30

Expert Comment

by:Reza Rad
ID: 33451548
this is code behind:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Configuration;
using SilverlightApplication.ServiceReference1;

namespace SilverlightApplication
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            Service1SoapClient wRef = new Service1SoapClient();
            wRef.GetSiteListCompleted += new EventHandler<GetSiteListCompletedEventArgs>(wRef_GetSiteListCompleted);
            wRef.GetSiteListAsync();
        }

        void wRef_GetSiteListCompleted(object sender, GetSiteListCompletedEventArgs e)
        {

            Site[] siteList = e.Result.ToArray();
            comboBox1.DataContext=sireList as IEnumerable<Site>;
            
        }



    }
}

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LVL 6

Author Comment

by:ged125
ID: 33451914
Reza_rad,  I tried your sample.   I get a Null Reference Exception on Line 30 of your snippet.
0
 
LVL 30

Expert Comment

by:Reza Rad
ID: 33452136
is the SiteList variable empty?
0
 
LVL 2

Accepted Solution

by:
FunctionUndefined earned 500 total points
ID: 33452468
I believe u deleted, unintentionally, a very important line from your MainPage() constructor, which should be something like
                  // Required to initialize variables
                  InitializeComponent();
Right now your combo is null/uninitialized since this method is missing. It is normally generated by the compiler, inside this method being hidden the C# code translation of your XAML page. Try to write this lines again in the constructor at the beginning; If it does not work, re-create the page.
0
 
LVL 6

Author Comment

by:ged125
ID: 33454835
Where is the main page constructor?
0
 
LVL 6

Author Comment

by:ged125
ID: 33454895
Disregard my last question, I wasn't awake yet.
0
 
LVL 6

Author Closing Comment

by:ged125
ID: 33454914
You nailed it!

From my original code snippet, I added the InitializeComponent(); method under MainPage() and bingo!

Thanks a bunch!
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