ListBox in front on the app

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If all the other controls means items in the ListBox then you are describing a ComboBox. There are various names for (types of) ComboBoxes. The name ComboBox refers to a combination of a ListBox and a TextBox although in the Windows API TextBoxes are called Edit Controls.

Your English is totally fine — and your question is very clear!
You’re describing a WinForms (Windows Forms) scenario:
You have a TextBox with autocomplete results shown in a ListBox, and when the ListBox displays many results, it pushes or moves other controls on the form. You want the ListBox to float on top, similar to a “z-index” in HTML/CSS.

Let’s fix that

Problem

When you add a ListBox directly inside the form’s layout (like in a Panel, TableLayoutPanel, or similar), it participates in the form’s layout and causes other controls to move or resize.

Solution 1: Show ListBox as a Floating Control (Independent Layer)

You can make the ListBox overlay other controls by setting it to TopMost and managing its position manually.

Here’s a simple example:

public partial class Form1 : Form
{
    ListBox lstSuggestions = new ListBox();
    
    public Form1()
    {
        InitializeComponent();
        
        // Initialize the ListBox
        lstSuggestions.Visible = false;
        lstSuggestions.Height = 100;
        lstSuggestions.Width = 200;
        lstSuggestions.BringToFront();  // makes it appear above other controls
        this.Controls.Add(lstSuggestions);

        textBox1.KeyUp += TextBox1_KeyUp;
        lstSuggestions.Click += LstSuggestions_Click;
    }

    private void TextBox1_KeyUp(object sender, KeyEventArgs e)
    {
        string text = textBox1.Text.ToLower();
        if (string.IsNullOrWhiteSpace(text))
        {
            lstSuggestions.Visible = false;
            return;
        }

        // Example items
        var allItems = new List { "Apple", "Apricot", "Banana", "Blueberry", "Cherry" };
        var filtered = allItems.Where(x => x.ToLower().StartsWith(text)).ToList();

        if (filtered.Count > 0)
        {
            lstSuggestions.DataSource = filtered;
            lstSuggestions.Visible = true;

            // Position the ListBox just below the TextBox
            lstSuggestions.Left = textBox1.Left;
            lstSuggestions.Top = textBox1.Bottom;
            lstSuggestions.BringToFront(); // ensure it's on top
        }
        else
        {
            lstSuggestions.Visible = false;
        }
    }

    private void LstSuggestions_Click(object sender, EventArgs e)
    {
        textBox1.Text = lstSuggestions.SelectedItem.ToString();
        lstSuggestions.Visible = false;
    }
}

What this does:

• Keeps the ListBox hidden until there are results.

• Positions it directly below the TextBox.

• Calls .BringToFront() so it overlaps other controls (like a popup).

• Does not move other controls anymore.

Solution 2: Use a Separate Form as Popup (Best for Professional Look)

If you want it to behave like a dropdown (similar to IntelliSense or combo box), create a small borderless Form and show it near your TextBox.

Form suggestionForm = new Form();
ListBox lstSuggestions = new ListBox();

private void InitializeSuggestionsPopup()
{
    suggestionForm.FormBorderStyle = FormBorderStyle.None;
    suggestionForm.ShowInTaskbar = false;
    suggestionForm.TopMost = true;

    lstSuggestions.Dock = DockStyle.Fill;
    suggestionForm.Controls.Add(lstSuggestions);
}

private void ShowSuggestions(Point location)
{
    suggestionForm.Location = location;
    suggestionForm.Size = new Size(200, 100);
    suggestionForm.Show();
}

This gives you a clean floating popup that never interferes with other controls.

Summary