一些Windows窗体控件无法识别？

Question

I have aa couple of ordinary Windows Forms. To clear the data entry fields in one of them I use code something like this:

    ClearInputFields(this);

    private void ClearInputFields(Control Page)
    {
        try
        {
            foreach (Control ctrl in Page.Controls)
            {
                if (ctrl is Button)                    
                    continue;
                if (ctrl is DataGridView)
                    continue;
                if (ctrl is ListBox)
                    continue;

                if (ctrl is TextBox)
                {
                    ((TextBox)(ctrl)).Text = string.Empty;
                }
                else if (ctrl is ComboBox)
                {        
                    ((ComboBox)(ctrl)).SelectedIndex = 0;
                }
                else if (ctrl is CheckBox)
                {
                    ((CheckBox)(ctrl)).Checked = false;
                }
                else if (ctrl.Controls.Count > 0)
                {
                    ClearInputFields(ctrl);
                }                                       
            }
        }
        catch (Exception ex)
        {
            TraceFile.Error("ExceptionLog", ex);
        }
    }

On one of the forms it works as expected. On the other form two out of nine ComboBoxs are NOT reset, and none of the six CheckBoxes are cleared.

Stepping through in the debugger, it appears that the particular controls are not even in the list of controls contained in the form.?!

I have compared the forms, and see nothing different in the properties of these controls. One of the comboBoxes that is not recognized is databound, one is not, but this is also true in the case of those that are reset.

I have looked at the designer, and all controls are declared as "this.Controls.Add(this.name_of_control);"

I have tried leaving out the last "else if" (there are no panels, group boxes, or other containers on this form anyway). No difference in behavior.

If I explicitly set the Checkboxes to "Checked = false", and set the ComboBoxes to "SelectedIndex = 0" they do what I expect, but not when iterating through the controls of the form.

EDIT - Addendum: All controls are created in the Designer, not at runtime. As mentioned, there are no containers on the form.

I expect this is one of those simple, obvious, right under your nose issues, but so far I'm not seeing it.

Any insights appreciated. Thanks!

Answer 1

Perhaps when changing a control's property – the order of the controls in this.Controls changes, so you're not going through all controls. Although maybe this is not the case because maybe the Control ctrl in Page.Controls is checked only the first time.

Answer 2

Whenever I have to do something on the items of a Collection that could alter it, I usually copy the collection and then loop through this copy. In your case this is the code that I usually write:

ClearInputFields(this);

private List<Control> ControlsForPage(Control Page)
{
        List<Control> result = new List<Control>();
        foreach (Control ctrl in Page.Controls)
              result.Add(ctrl);
        return result;
{

private void ClearInputFields(Control Page)
{
    try
    {
        List<Control> ctrlsCopy = ControlsForPage(Page);
        foreach (Control ctrl in ctrlsCopy)
        {
            if (ctrl is Button)                    
                continue;
            if (ctrl is DataGridView)
                continue;
            if (ctrl is ListBox)
                continue;

            if (ctrl is TextBox)
            {
                ((TextBox)(ctrl)).Text = string.Empty;
            }
            else if (ctrl is ComboBox)
            {        
                ((ComboBox)(ctrl)).SelectedIndex = 0;
            }
            else if (ctrl is CheckBox)
            {
                ((CheckBox)(ctrl)).Checked = false;
            }
            else if (ctrl.Controls.Count > 0)
            {
                ClearInputFields(ctrl);
            }                                       
        }
    }
    catch (Exception ex)
    {
        TraceFile.Error("ExceptionLog", ex);
    }
}

Anyway, just to understand what's going on here, I would try to make the copy of Controls before doing your reset, and then compare it with the Controls collection of your page after the reset.