.NET (Core and Framework)

public partial class Form1 : Form
{
    Panel panela = new Panel();
    ComboBox comboBox1 = new ComboBox();

    public Form1()
    {
        InitializeComponent();

        this.panela.Name = "panel";
        this.panela.Size = new Size((int)(this.ClientSize.Width * 0.765), (int)(this.ClientSize.Height * 0.75));
        this.panela.BackColor = Color.SteelBlue;
        this.panela.Hide();
        this.panela.Parent = this;

        this.comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
        this.comboBox1.Items.AddRange(new string[] { "item1", "item2", "item3" });
        this.comboBox1.SelectedIndexChanged += new EventHandler(comboBox1_SelectedIndexChanged);
    }

    void button1_Click(object sender, EventArgs e)
    {
        this.panela.Location = new Point((this.ClientSize.Width / 2) - (this.panela.ClientSize.Width / 2), (this.ClientSize.Height / 2) - (this.panela.ClientSize.Height / 2));

        int width = (int)(this.panela.ClientSize.Width * 0.965);
        int height = (int)(this.panela.ClientSize.Height * 0.95);

        Panel panelb = new Panel();
        panelb.Size = new Size(width, height);
        panelb.Location = new Point((this.panela.ClientSize.Width / 2) - (width / 2), (this.panela.ClientSize.Height / 2) - (height / 2));
        panelb.BackColor = Color.White;

        Rectangle parentRect = panelb.ClientRectangle;
        int maxWidth = parentRect.Width - 4;

        this.comboBox1.Bounds = new Rectangle(parentRect.Left + 2, parentRect.Top + 2, maxWidth, this.comboBox1.Height);
        this.comboBox1.SelectedIndex = -1;
        this.comboBox1.Parent = panelb;

        Button ok = new Button();
        ok.Bounds = new Rectangle(parentRect.Width - ok.Width, parentRect.Bottom - ok.Height, 72, 23);
        ok.Text = "OK";
        ok.FlatStyle = FlatStyle.System;
        ok.Click += new EventHandler(ok_Click);
        ok.Parent = panelb;

        panelb.Parent = this.panela;

        this.panela.Show();
        this.panela.BringToFront();
    }

    void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        MessageBox.Show("index changed");
    }

    void ok_Click(object sender, EventArgs e)
    {
        this.comboBox1.SelectedIndex = -1;

        this.panela.Hide();
        this.comboBox1.Parent.Controls.Remove(this.comboBox1);

        int count = this.panela.Controls.Count;
        int i = 0;
        while (i < count)
        {
            this.panela.Controls[0].Dispose();
            i++;
        }
    }
}

tuga-x wrote:

Ok, so I'm not hallucinating, something really strange is going on here.

I'm inclined to think it's a bug, but I don't really know.

Obviously there are ways around this, but I shouldn't have to do them. I'm not doing anything special!

Luc Pattyn wrote:

[Added] I typically don't call dispose on controls, except for forms/dialogs, since
my controls tend to always be part of some Form, and I trust .NET to dispose properly
of the Controls that are used on a Form that gets Closed or Disposed.[/added]

Patrick Sears wrote:

you shouldn't call Dispose on controls and GUIs

Patrick Sears wrote:

If you want to remove the control from the parent collection, do that. Don't invent some convoluted system of destruction just to remove a control from the parent collection.

int a=12;
string s=a.ToString();