winform - autocomplete textbox based on typed history

In addition/alternative to the Solution by Box I would add the following:

1) For history storage, use System.Collections.Generic.SortedList, it will provide better performance in filtering our duplicates.

2) Do not trigger adding an item to the history by any UI "raw" events like LostFocus, etc. Trigger if by a semantic even, when you code actually uses the data from a text box.

3) For persistence between run-times, a database could be bit of overkill. Use just an XML file representing state of the application (maybe all Finite State Machine, not just history). The file should be placed in the directory found by the call System.Environment.GetFolderPath(System.Environment.SpecialFolder.LocalApplicationData). For serialization, see DataContract; see System.Runtime.Serialization.DataContractSerializer, System.Runtime.Serialization.DataContractAttribute, System.Runtime.Serialization.DataMemberAttribute. This method is most non-intrusive an flexible at the same time.

—SA

I think BobJanova's answer is very good (follow his advices for storing an syncronizing). A little msdn reading should solve your problem (but that is true for a lot of questions here).
Anyway I created an executable example for you (just copy in a new WinForms Project and replace Program.cs with following code:)

using System;
using System.Collections.Generic;
using System.Windows.Forms;
namespace AutoComplete
{
    static class Program
    {
        [STAThread] // You have to set STA when using AutoCompleteCustomSource !!!!
        static void Main()
        {
            // Create a Form 
            Form form = new Form();
            // ... and a description Label 
            Label label = new Label();
            label.Text = "I will remember";
            label.Dock = DockStyle.Top;
            // Now create a TexBox  
            TextBox textbox = new TextBox();
            textbox.Dock = DockStyle.Top;
            // ... and enable AutoComplete
            textbox.AutoCompleteMode = AutoCompleteMode.SuggestAppend; // Set the AutoCompleteMode you like
            textbox.AutoCompleteSource = AutoCompleteSource.CustomSource; // we will use a custome source (the entered text)
            // create a button to simulate validate/lost focus (whatever your real strategy will be)
            Button button = new Button();
            button.Dock = DockStyle.Top;
            button.Text = "Add to history";
            // if the button is clicked the text should be added to history 
            button.Click += delegate(object sender, EventArgs e)
            {
                // add a new text to the AutoCompleteCustomSource list
                string strTextToAdd = textbox.Text;
                if (!String.IsNullOrWhiteSpace(strTextToAdd))// in reality you will want filter or validate the text
                {
                    textbox.AutoCompleteCustomSource.Add(strTextToAdd);
                }
                // lets clear the textbox after that in this example
                textbox.Text = String.Empty;
                // ...  and refocus it
                textbox.Focus();
            };
            // Add all the Controls to the Form
            form.Controls.Add(button);
            form.Controls.Add(textbox);
            form.Controls.Add(label);
            // ... and show the form
            Application.Run(form);
        }
    }
}

I have a suggestion which might be helpful or give some idea
Write a client side event on lose focus event on the textbox (on which you want to auto complete functionality), and store the value of text box into the cookie from java script, and use this cookie for the auto complete. Read the content of the cookie, make an array and can use JQuery autocomplete extender.

HI Anil,

Windows application doesn't provide any specific location like cookies or Browser History in Web, to store previosly typed values.

For WinForms, You need to create your own history.
You can use XML Files to store the history.
And at the time of User Input, You can fetch data from that XML.

regards
Ankit