TextBox Autocomplete with .NET Core 3.0

Load data in another thread and free the User Interface.

.NET Core 3.0 is the latest version of .NET Core and now supports WinForms and WPF. This sample shows how you can perform fill data to Autocomplete TextBox in another thread without slowing down the main UI (User Interface). With this sample, you can create a better user experience for the end-user.

 

TextBox Autocomplete

 

Autocomplete helps the user to search/type from a known list. In my application, I built a list to Autocomplete with > 10.000 items and is very fast even on slow computers.

 

Autocomplete is an old feature, but this post will demonstrate how to perform this to load data quickly in NET Core 3.0.

 

When you fill a Collection, if you have a huge suggestion list, this will make the UI (User Interface) freeze. But if you process it in another thread the UI will not have any issues.

  

More technical information is here.

 

How it works

 

 Like the other POST that uses a delegate, here, we use another thread to load data and delegate to bind the Autocomplete Collection in the current UI thread.

using System;
using System.Data.SqlClient;
using System.Drawing;
using System.Windows.Forms;

namespace TextBoxWithAutoComplete
{

    /// <summary>
    /// 10-10-2019
    /// </summary>
    public partial class Form1 : Form
    {

        private TextBox textBox1;
        public Form1()
        {
            InitializeComponent();

            textBox1 = new TextBox
            {
                Location = new Point(0, 0),
                Size = new Size(100, 32),
                Visible = true,
                TabIndex = 0
            };
            Controls.Add(textBox1);

            Load += Form1_Load;
        }

        public void Form1_Load(object sender, EventArgs e)
        {
            Show(); // You need to show the form to avoid a thread error

            LoadData(); // Start to load Data
        }

        private SqlConnection GetConnection()
        {
            // Init your connection
            var oCnn = new SqlConnection
            {
                ConnectionString = "YOUR_CONNECTION_STRING"
            };
            oCnn.Open();
            return oCnn;
        }


        #region TreadSafeLoading
        private delegate void UpdateUIDelegate(AutoCompleteStringCollection myCollection);

        /// <summary>
        /// Load Data - You can make public to load as you need
        /// </summary>
        private void LoadData()
        => // Start this process in a new thread
            new System.Threading.Thread(() => OutOfThreadProcess()).Start();
        // You can start others, every one in a new thread!

        /// <summary>
        /// Start fill in another Thread
        /// </summary>
        private void OutOfThreadProcess()
        {
            // inialize the collection
            var myCollection = new AutoCompleteStringCollection();
            using var oCnn = GetConnection();

            // Start your SQL Query
            var cmd = new SqlCommand($"Select [FirstName] + ' ' + [LastName] as [contactName] From [AdventureWorks].[Person].[Contact] Order By [FirstName], [LastName]", oCnn);

            // Read and fill the collection
            using var reader = cmd.ExecuteReader();
            while (reader.Read())
                myCollection.Add(reader.GetString(0));

            // Invoke in a UI thread
            _ = Invoke(new UpdateUIDelegate(UpdateUIInvoke), myCollection);
        }

        /// <summary>
        /// Current UI Thread threatment
        /// </summary>
        /// <param name="myCollection"></param>
        private void UpdateUIInvoke(AutoCompleteStringCollection myCollection)
        {
            // Setup up in corrent UI Thread
            textBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            textBox1.AutoCompleteCustomSource = myCollection;
#if (IS_TELERIK_RadTextBoxControl)
            // If you use Telerik
            // I found an issue in Telerik by Progress, without fix.
            if (ParentForm != null)
                ParentForm.FormClosing += new FormClosingEventHandler(UIFormClosing);
#endif
        }
#if (IS_TELERIK_RadTextBoxControl)
        private void UIFormClosing(object sender, FormClosingEventArgs e) => textBox1.AutoCompleteCustomSource = null;

#endif
        #endregion

    }
}

Observation

 

When you use this technique you may receive errors if you run the new thread without firing the Show() method from the form, this occurs because the current window(form) hasn't initialized.

 

Conclusion

 

I designed this technique when I upgraded to .NET Core 3 and developed a fix for the FileSystemWatcher event that fires in a new thread, so I took the same idea to make Autocomplete load collection work in a new thread.

 

I hope you can bring a better experience to your end-users.

 

Happy coding.