I want to refer to controls by variable name

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I have a winforms project which changes a property (Tag) of a control (comboBox or textBox) when the value is changed. I'd like to put the change code in a method:-

private void TagControl(string CtrlName, string CtrlText, string CtrlValue )
   {
       if (tabControlPeople.Controls[CtrlName].Tag is null)
           {
           ChangesItem.Add(CtrlText);
           ChangesValue.Add(CtrlValue);
           tabControlPeople.Controls[CtrlName].Tag = "Changed";
       }
       else
       {
           if (ChangesItem.IndexOf(CtrlText)!=-1)
           {
               j = ChangesItem.IndexOf(CtrlText);
               ChangesValue[j] = CtrlName;
           }
           else
           {
               MessageBox.Show("Error correcting " + CtrlText);
           }
       }
   }

This is called by:-

TagControl("comboBoxPeople4", "SecurityGroupID", comboBoxPeople4.SelectedValue.ToString());

The controls are on a tabcontrol (tabControlPeople) on a panel (panelPeople) on a form (Form1).
I get an error 'Object reference not set to an instance of an object'.

What I have tried:

Using this.Controls[......]
using panelPeople.Controls[......]
using tabControlPeople.Controls[......]
using this.panelPeople.Controls[.....]
using this.tabControlPeople.Controls[.....]

Posted 14-Nov-21 15:36pm

ormonds

Updated 14-Nov-21 17:23pm

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Wendelius · Answer 1 · 2021-11-14T16:24:00

The easiest way to find the reason is to put a breakpoint to the line calling your method. Using debugger proceed line by line and investigate the variables and collections to see where the exception is thrown and why.

For example possible reasons are, you've misspelled the control name, the control is not in the collection you suspect etc. By investigating the collections with the debugger, it's easy to see the names and the locations of your controls.

For more info about debugging, have a look at
- First look at the debugger - Visual Studio (Windows) | Microsoft Docs[^]
- Tutorial: Debug C# code - Visual Studio (Windows) | Microsoft Docs[^]

ormonds · Answer 2 · 2021-11-14T17:23:00

Got it:
[^]
I needed to get the control name properly:

ComboBox ThisBox = (ComboBox) this.GetControlByName(this, CtrlName);

and

public Control GetControlByName(Control ParentCntl, string NameToSearch)
{
    if (ParentCntl.Name == NameToSearch)
        return ParentCntl;
    foreach (Control ChildCntl in ParentCntl.Controls)
    {
        Control ResultCntl = GetControlByName(ChildCntl, NameToSearch);
        if (ResultCntl != null)
            return ResultCntl;
    }
    return null;
}

I want to refer to controls by variable name

2 solutions

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Solution 2

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I want to refer to controls by variable name

2 solutions

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