`SelectedIndexChanged` fires event when I set dataset of a different combobox

Question

This is a problem from Windows Mobile 6.5 (.net compact edition)in Windows Forms. I have created a form with two usercontrols, each containing one combobox.
When I load the second usercontrol, I fill the combobox and fire _SelectedIndexChanged of the combobox of the first usercontrol. This error only happen when in the first usercontrol there's a control datagrid. if u delete datagrid all events are corrects.

 public partial class Form1 : Form
{
    static void Main(string[] args)
    {
        Application.Run(new Form1());
    }

    private UserControl1 userControl1 = null;
    private UserControl2 userControl2 = null;

    public Form1()
    {
        InitializeComponent();
        InitializeUserControl();
    }

    private void InitializeUserControl()
    {
        InitiliazeTab1();
        InitiliazeTab2();
    }

    private void InitiliazeTab1()
    {
        userControl1 = new UserControl1();
        userControl1.Dock = DockStyle.Fill;

        TabPage oTabpage1 = new TabPage();
        oTabpage1.Name = "tabSeleccionTipo1";
        oTabpage1.Text = "Tipo1 ";
        oTabpage1.Controls.Add(userControl1);
        tabControl1.TabPages.Add(oTabpage1);

        userControl1.LoadComponent();
    }

    private void InitiliazeTab2()
    {
        userControl2 = new UserControl2();
        userControl2.Dock = DockStyle.Fill;

        TabPage oTabpage2 = new TabPage();
        oTabpage2.Name = "tabSeleccionTipo2";
        oTabpage2.Text = "Tipo2 ";
        oTabpage2.Controls.Add(userControl2);
        tabControl1.TabPages.Add(oTabpage2);

        userControl2.LoadComponent();
    }
}

partial class Form1
{
    /// <summary>
    /// Variable del diseñador requerida.
    /// </summary>
    private System.ComponentModel.IContainer components = null;
    private System.Windows.Forms.MainMenu mainMenu1;

    /// <summary>
    /// Limpiar los recursos que se estén usando.
    /// </summary>
    /// <param name="disposing">true si los recursos administrados se deben eliminar; en caso contrario, false.</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Código generado por el Diseñador de Windows Forms

    /// <summary>
    /// Método necesario para admitir el Diseñador. No se puede modificar
    /// el contenido del método con el editor de código.
    /// </summary>
    private void InitializeComponent()
    {
        this.mainMenu1 = new System.Windows.Forms.MainMenu();
        this.tabControl1 = new System.Windows.Forms.TabControl();
        this.SuspendLayout();
        // 
        // tabControl1
        // 
        this.tabControl1.Location = new System.Drawing.Point(0, 0);
        this.tabControl1.Name = "tabControl1";
        this.tabControl1.SelectedIndex = 0;
        this.tabControl1.Size = new System.Drawing.Size(240, 265);
        this.tabControl1.TabIndex = 0;
        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(96F, 96F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi;
        this.AutoScroll = true;
        this.ClientSize = new System.Drawing.Size(240, 268);
        this.Controls.Add(this.tabControl1);
        this.Menu = this.mainMenu1;
        this.Name = "Form1";
        this.Text = "Form1";
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.TabControl tabControl1;
}

Usercontrols are UserControl1 and UserControl2.

public partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        InitializeComponent();
    }

    public void LoadComponent()
    {
        this.comboBox1.ValueMember = "Clave";
        this.comboBox1.DisplayMember = "Description";
        comboBox1.DataSource = getList();         
    }

    private List<Item> getList()
    {
        List<Item> list = new List<Item>();

        list.Add(new Item("0", "zero"));
        list.Add(new Item("1", "uno"));
        list.Add(new Item("2", "dos"));
        list.Add(new Item("3", "tres"));
        list.Add(new Item("4", "cuatro"));

        return new List<Item>(list);
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        MessageBox.Show("Listo 1 ^^ SelectedIndexChanged ");    
    }
}

partial class UserControl1
{
    /// <summary> 
    /// Variable del diseñador requerida.
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary> 
    /// Limpiar los recursos que se estén usando.
    /// </summary>
    /// <param name="disposing">true si los recursos administrados se deben eliminar; en caso contrario, false.</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Código generado por el Diseñador de componentes

    /// <summary> 
    /// Método necesario para admitir el Diseñador. No se puede modificar 
    /// el contenido del método con el editor de código.
    /// </summary>
    private void InitializeComponent()
    {
        this.comboBox1 = new System.Windows.Forms.ComboBox();
        this.dataGrid1 = new System.Windows.Forms.DataGrid();
        this.SuspendLayout();
        // 
        // comboBox1
        // 
        this.comboBox1.Location = new System.Drawing.Point(24, 24);
        this.comboBox1.Name = "comboBox1";
        this.comboBox1.Size = new System.Drawing.Size(163, 22);
        this.comboBox1.TabIndex = 6;
        this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);
        // 
        // dataGrid1
        // 
        this.dataGrid1.BackgroundColor = System.Drawing.Color.FromArgb(((int)(((byte)(128)))), ((int)(((byte)(128)))), ((int)(((byte)(128)))));
        this.dataGrid1.Location = new System.Drawing.Point(24, 89);
        this.dataGrid1.Name = "dataGrid1";
        this.dataGrid1.Size = new System.Drawing.Size(163, 134);
        this.dataGrid1.TabIndex = 7;
        // 
        // UserControl1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(96F, 96F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi;
        this.Controls.Add(this.dataGrid1);
        this.Controls.Add(this.comboBox1);
        this.Name = "UserControl1";
        this.Size = new System.Drawing.Size(216, 266);
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.ComboBox comboBox1;
    private System.Windows.Forms.DataGrid dataGrid1;

}

public partial class UserControl2 : UserControl
{
    public UserControl2()
    {
        InitializeComponent();
    }

    public void LoadComponent()
    {
        this.comboBox2.ValueMember = "Clave";
        this.comboBox2.DisplayMember = "Description";
        this.comboBox2.DataSource = getList();
    }

    public List<Item> getList()
    {
        List<Item> list = new List<Item>();
        list.Add(new Item("0", "zero"));
        list.Add(new Item("1", "uno"));
        list.Add(new Item("2", "dos"));
        list.Add(new Item("3", "tres"));
        return new List<Item>(list);
    }

    private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
    {
        MessageBox.Show("Listo 2 ^^ SelectedIndexChanged ");      
    }
}

partial class UserControl2
{
    /// <summary> 
    /// Variable del diseñador requerida.
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary> 
    /// Limpiar los recursos que se estén usando.
    /// </summary>
    /// <param name="disposing">true si los recursos administrados se deben eliminar; en caso contrario, false.</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null))
        {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Código generado por el Diseñador de componentes

    /// <summary> 
    /// Método necesario para admitir el Diseñador. No se puede modificar 
    /// el contenido del método con el editor de código.
    /// </summary>
    private void InitializeComponent()
    {
        this.comboBox2 = new System.Windows.Forms.ComboBox();
        this.SuspendLayout();
        // 
        // comboBox2
        // 
        this.comboBox2.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDown;
        this.comboBox2.Location = new System.Drawing.Point(21, 27);
        this.comboBox2.Name = "comboBox2";
        this.comboBox2.Size = new System.Drawing.Size(163, 22);
        this.comboBox2.TabIndex = 0;
        this.comboBox2.SelectedIndexChanged += new System.EventHandler(this.comboBox2_SelectedIndexChanged);
        // 
        // UserControl2
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(96F, 96F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi;
        this.Controls.Add(this.comboBox2);
        this.Name = "UserControl2";
        this.Size = new System.Drawing.Size(216, 266);
        this.ResumeLayout(false);

    }

    #endregion

    private System.Windows.Forms.ComboBox comboBox2;
}

This is a simplified version of the real code. Why does this event fire when I load datasource of combobox of the second usercontrol?

call process pool image of pool process of events.

Answer 1

I have resolved incorporated a datagrid in each usercontrol. This error isn't logical, it should be about framework librery error.

thanks.

Answer 2

Try subscribing to the SelectionChangeCommitted event instead

This way it doesn't fire when the change is made programmatically, which is the case of datasource loading

Answer 3

First some minor, cosmetic changes:

write

private List<Item> getList()
{
    ...
    return list;
}

instead of

public List<Item> getList()
{
    ...
    return new List<Item>(list);
}

Then move the event handler assignment:

    this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);

from designer code to LoadComponent()

    public void LoadComponent()
    {
        this.comboBox1.ValueMember = "Clave";
        this.comboBox1.DisplayMember = "Description";
        comboBox1.DataSource = getList();
        this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);
    }

The issue can be worked around by removing the DataGrid from the first loaded UserControl. For example, the issue will not show if the DataGrid is on the second loaded UserControl:

    private void InitializeUserControl()
    {
        InitiliazeTab2();
        InitiliazeTab1();
    }

There is no way to find the root cause, why the ComboBox SelectedIndexChanged event fires when the DataGrid is loaded within the first UserControl. There is no logical, documented description for that and I know no way to debug the event bubbling of Compact Framework.

For easy test of others, here is a VS2005 project to play with: https://github.com/hjgode/StackOverflow/tree/master/SmartDeviceProject1