C# WinForms ErrorProvider Control

This falls in the category of "how can you not know". It is your code that is calling ErrorProvider.SetError(), you should have no trouble keeping track of how many errors are still active. Here's a little helper class, use its SetError() method to update the ErrorProvider. Its Count property returns the number of active errors:

private class ErrorTracker {
  private HashSet<Control> mErrors = new HashSet<Control>();
  private ErrorProvider mProvider;

  public ErrorTracker(ErrorProvider provider) { 
    mProvider = provider; 
  }
  public void SetError(Control ctl, string text) {
    if (string.IsNullOrEmpty(text)) mErrors.Remove(ctl);
    else if (!mErrors.Contains(ctl)) mErrors.Add(ctl);
    mProvider.SetError(ctl, text);
  }
  public int Count { get { return mErrors.Count; } }
}

Today I had the same problem. My solution is to extend the ErrorProvider control.

See the code below:

  public class MyErrorProvider : ErrorProvider
  {

    public List<Control> GetControls()
    {
      return this.GetControls(this.ContainerControl);
    }

    public List<Control> GetControls(Control ParentControl)
    {
      List<Control> ret = new List<Control>();

      if (!string.IsNullOrEmpty(this.GetError(ParentControl)))
        ret.Add(ParentControl);

      foreach (Control c in ParentControl.Controls)
      {
        List<Control> child = GetControls(c);
        if (child.Count > 0)
          ret.AddRange(child);
      }

      return ret;
    }
  }

You can use the above derived class in your form, and then (say that myErrorProvider is the class instance in your form) you can get all the controls with errors in your form, by calling:

List<Control> errorControls = myErrorProvider.GetControls();