ComboBox selection changed event : ComboBox : GUI Windows Forms C# Examples

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

public  class  ComboBoxes  :  Form
{
    ComboBox  cmb;
    Button  btnDisplay;
    Button  btnInsert;
    Button  btnSelect;
    Label  lblEdit;
    TextBox  txtDisplay;
    Boolean  boolChange  =  false;
    Boolean  boolProcessed  =  false;

    public  ComboBoxes()
    {
        Size  =  new  Size(300,400);
        this.Load  +=  new  EventHandler(this_Load);

        cmb  =  new  ComboBox();
        cmb.Parent  =  this;
        cmb.Location  =  new  Point(10,10);
        cmb.Size  =  new  Size(ClientSize.Width  /  2,  Height  -  200);
        cmb.Anchor  =  AnchorStyles.Top  |  AnchorStyles.Left  |  AnchorStyles.Right  |  AnchorStyles.Bottom;
        cmb.DropDownStyle  =  ComboBoxStyle.DropDown;        
        cmb.DropDownStyle  =  ComboBoxStyle.Simple;
        cmb.DropDownWidth  =  (int)(cmb.Width  *  1.5);
        cmb.MaxDropDownItems  =  12;
        cmb.MaxLength  =  20;

        cmb.SelectionChangeCommitted  +=  new  EventHandler(cmb_SelectionChangeCommitted);
        cmb.Leave  +=  new  EventHandler(cmb_Leave);

        btnInsert  =  new  Button();
        btnInsert.Parent  =  this;
        btnInsert.Text  =  "&Insert  Item";
        btnInsert.Size  =  new  Size((int)(Font.Height  *  .75)  *  btnInsert.Text.Length,  cmb.Height);
        btnInsert.Location  =  new  Point(cmb.Right  +  10,  cmb.Top);
        btnInsert.Click  +=  new  System.EventHandler(btnInsert_Click);

        lblEdit  =  new  Label();
        lblEdit.Parent  =  this;
        lblEdit.BorderStyle  =  BorderStyle.Fixed3D;
        lblEdit.Location  =  new  Point(cmb.Left,  cmb.Bottom  +  10);
        lblEdit.BackColor  =  Color.LightGray;
        lblEdit.Text  =  "";
        lblEdit.Size  =  new  Size(cmb.DropDownWidth,  Font.Height  *  2);

        btnDisplay  =  new  Button();
        btnDisplay.Parent  =  this;
        btnDisplay.Text  =  "&Display  Items";
        btnDisplay.Size  =  new  Size((int)(Font.Height  *  .75)  *  btnDisplay.Text.Length,  cmb.Height);
        btnDisplay.Location  =  new  Point(lblEdit.Left,  lblEdit.Bottom  +  10);
        btnDisplay.Click  +=  new  System.EventHandler(btnDisplay_Click);

        txtDisplay  =  new  TextBox();
        txtDisplay.Parent  =  this;
        txtDisplay.Location  =  new  Point(btnDisplay.Left,  btnDisplay.Bottom  +  10);
        txtDisplay.Multiline  =  true;
        txtDisplay.ReadOnly  =  true;
        txtDisplay.BackColor  =  Color.LightGray;
        txtDisplay.ScrollBars  =  ScrollBars.Vertical;
        txtDisplay.Text  =  "";
        txtDisplay.Size  =  new  Size(cmb.DropDownWidth,  200);
        
        btnSelect  =  new  Button();
        btnSelect.Parent  =  this;
        btnSelect.Text  =  "&Select  4";
        btnSelect.Size  =  new  Size((int)(Font.Height  *  .75)  *  btnSelect.Text.Length,  cmb.Height);
        btnSelect.Location  =  new  Point(btnDisplay.Right  +  10,  btnDisplay.Top);
        btnSelect.Click  +=  new  System.EventHandler(btnSelect_Click);

            cmb.Items.Add("A");
            cmb.Items.Add("B");
            cmb.Items.Add("C");
            cmb.Items.Add("D");
            cmb.Items.Add("E");                                                
        cmb.SelectedIndex  =  0;      
    }

    static  void  Main()  
    {
        Application.Run(new  ComboBoxes());
    }

    private  void  this_Load(object  sender,  EventArgs  e)
    {
        cmb.TextChanged  +=  new  EventHandler(cmb_TextChanged);
        cmb.SelectedIndexChanged  +=  new  EventHandler(cmb_SelectedIndexChanged);
    }

    private  void  cmb_TextChanged(object  sender,  EventArgs  e)
    {
        if  (!boolProcessed)
            lblEdit.Text  =  cmb.Text;
        boolChange  =  true;
    }        
    private  void  cmb_SelectedIndexChanged(object  sender,  EventArgs  e)
    {
        if  (boolChange)
        {
            boolChange  =  false;
            boolProcessed  =  false;
        }
    }

    private  void  cmb_SelectionChangeCommitted(object  sender,  EventArgs  e)
    {
        if  (boolChange)
            ProcessChange();
    }        

    private  void  cmb_Leave(object  sender,  EventArgs  e)
    {
        if  (boolChange)
        {
            ProcessChange();
            boolChange  =  false;
        }
    }        

    private  void  ProcessChange()
    {
        lblEdit.Text  =  "Edited:  "  +  cmb.Text;
        boolProcessed  =  true;
    }

    private  void  btnDisplay_Click(object  sender,  EventArgs  e)
    {
        string  str  =  DateTime.Now.ToString()  +  "\r\n";
        foreach  (object  item  in  cmb.Items)
        {
            str  +=  item.ToString()  +  "\r\n";
        }

        txtDisplay.Text  =  str;
    }        

    private  void  btnSelect_Click(object  sender,  EventArgs  e)
    {
        cmb.Select(1,2);
    }        

    private  void  btnInsert_Click(object  sender,  EventArgs  e)
    {
        if  (cmb.FindStringExact(cmb.Text)  !=  -1)
        {
            MessageBox.Show("'"  +  cmb.Text  +  "'  already  exists  in  the  list.\r\n"  +  
                    "Will  not  be  added  again.",
                    "Already  Exists!");
        }
        else  if  (cmb.Text  ==  "")
        {
            MessageBox.Show("There  is  nothing  to  add.","Nothing  There");
        }
        else
        {
            cmb.Items.Add(cmb.Text);
        }
    }
}