C# error provider not working on textboxes in groupbox and tabcontrols

Question

I am trying to implement using error provider to validate that my text boxes are not empty before proceeding with execution.

Error provider works on textboxes on th

Answer 1

This is because your code does not check the child controls and only checks the top level ones. You need to iterate through the Form's controls recursively:

private IEnumerable GetAllControls(Control control)
{
    var controls = control.Controls.Cast();
    return controls.SelectMany(ctrl => GetAllControls(ctrl)).Concat(controls);
}

private void button1_Click(object sender, EventArgs e)
{
    errorProvider1.Clear();
    foreach (Control c in GetAllControls(this))
    {
        if (c is TextBox && string.IsNullOrEmpty(c.Text))
            errorProvider1.SetError(c, "Error");
    }
}

Or, Linq way:

errorProvider1.Clear();

GetAllControls(this).Where(c => c is TextBox && string.IsNullOrEmpty(c.Text))
    .ToList()
    .ForEach(c => errorProvider1.SetError(c, "Error"));

Good luck.