Index of control is -1 in C#

Question

Hi, I am trying to get the index of a textbox control in WinForms, so I am using this:
var index = Controls.IndexOf(textBox24);
MessageBox.Show(index.ToString());
Now when I run the app, and click on the textbox, it shows the index as -1. Why? Because of the index being -1, I am having problems in using the textbox in some piece of code.

Answer 1

Is textBox24 apart of the current control or possibly apart of a nested control?

Answer 2

Why not use this

var results = Controls.Find("textBox24", true);
if (results.Length == 1)
{
    // found it
    ((TextBox)results[0]).Text = "OK";
}
else
{
    // did not find it
}

Or

if (Controls.Find("textBox24", true).FirstOrDefault() is TextBox textBox)
{
    textBox.Text = "OK";
}

Answer 3

If the text box may have been positioned as shown in the following picture,

Then, you can use this.

private void button1_Click(object sender, EventArgs e)  
{  
    var index = Controls.IndexOf(this.textBox24);  
    MessageBox.Show(index.ToString()); // -1  

    var i1 = groupBox1.Controls.IndexOf(this.textBox1);  
    MessageBox.Show(i1.ToString());  

    var v1 = Controls.Find(this.textBox1.Name, true).FirstOrDefault();  
    MessageBox.Show(v1.TabIndex.ToString()); // Not -1  
}