CODEWITHSUNDEEP
c#wpflinqcombobox
Dan.
Dan.

Reputation: 717

Fill ComboBox with Results of LINQ Query, Directly

I am new to c#/.net/WPF.

I am trying to fill a combobox with values taken from a database.

The LINQ query gets a list of all companies in the database and the code attempts to fill a ComboBox control with this list.

The C# code below successfully gets the results (I previously outputted it with a MessageBox.Show()).

My Next step was to remove that bit and, instead, put in the code which would fill out this ComboBox:

<ComboBox Name="companyComboBox"/>

The c#:

    using System;
    using System.Collections;
    using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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.Shapes;
using System.Data.SqlClient;
using System.Data.Linq;
using System.Data.Linq.Mapping;

namespace LeadSystem
{
    /// <summary>
    /// Interaction logic for NewLead.xaml
    /// </summary>
    public partial class NewLead : Window
    {

    public NewLead()
    {


       // Use a connection string.
        DataContext db = new DataContext("Data Source=HP\\SQLEXPRESS;Initial Catalog=LeadSystem;Integrated Security=True");

        // Get a typed table to run queries.
        Table<Company> Companies = db.GetTable<Company>();

        // Attach the log to show generated SQL.
        db.Log = Console.Out;

        // Query for all companies.
        var companyQuery = 
            from c in Companies
            select new { Name = c.CompanyName, ID = c.CompanyID };

        companyComboBox.ItemsSource = companyQuery.ToList();
        companyComboBox.DisplayMemberPath = "Name";
        companyComboBox.SelectedValuePath = "ID";
        InitializeComponent();

    }
}
}

The problem I keep getting is:

Object reference not set to an instance of an object.

^ it's talking about companyQuery, where I try to use it to fill the comboBox.

I thought this must be because of deferred execution, and so I had a look around the web to find a solution. I've seen several people say to add ToList() at the end of that line of code, but nothing changed.

So, does someone here know what I'm doing wrong??

I have looked around the web (including Stackoverflow) and nothing has helped me fix mine.

Also, if it's not too cheeky to ask two questions in one go... How do I set the selected value and displayed values in my ComboBox? Is it correct, the way I already have it?

Thanks

Upvotes: 4

Views: 12941

Answers (2)

Reece Kenney
Reece Kenney

Reputation: 2964

Put InitializeComponent(); before you set the itemSource

Upvotes: 0

Chino
Chino

Reputation: 821

Try to fill the companyComboBox after the initializeComponent

 InitializeComponent();
    companyComboBox.ItemsSource = companyQuery.ToList();
    companyComboBox.DisplayMemberPath = "Name";
    companyComboBox.SelectedValuePath = "ID";

Upvotes: 6

Related Questions