Looping through controls

Question

In my code I need to loop through the controls in a GroupBox and process the control only if it a ComboBox. I am using the code:

foreach (System.Windows.Forms.Control grpbxChild in this.gpbx.Controls)
{
    if (grpbxChild.GetType().Name.Trim() == "ComboBox")
    {
        // Process here
    }
}

My question is: Instead of looping through all the controls and processing only the combo boxes is is possible to get only the combo boxes from the GroupBox? Something like this:

foreach (System.Windows.Forms.Control grpbxChild in this.gpbx.Controls.GetControlsOfType(ComboBox))
{
    // Process here
}

score 8 · Accepted Answer · edited Aug 31 '10 at 13:55

8

Since you are using C# 2.0, you're pretty much out of luck. You could write a function yourself. In C# 3.0 you'd just do:

foreach (var control in groupBox.Controls.OfType<ComboBox>())
{
    // ...
}

C# 2.0 solution:

public static IEnumerable<T> GetControlsOfType<T>(ControlCollection controls)
    where T : Control
{
    foreach(Control c in controls)
        if (c is T)
            yield return (T)c;
}

which you'd use like:

foreach (ComboBox c in GetControlsOfType<ComboBox>(groupBox.Controls))
{
    // ...
}

edited Aug 31 '10 at 13:55

abatishchev

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answered May 15 '09 at 09:37

Mehrdad Afshari

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+1 for mentioning the OfType syntax, but the presented "pseudosolution" still requires a loop through all the child controls. Which doesn't address the basic problem. – Cerebrus May 15 '09 at 09:44
@Cerebrus: It doesn't require a loop if you don't need to do anything with it. If you just want the collection of ComboBoxes you could just do: List list = new List(GetControlsOfType(groupBox.Controls)); – Mehrdad Afshari May 15 '09 at 09:46
Thanks Mehrdad... this works!!! Don't call it pseudosolution. It is the solution. You were just short of the where clause. Please edit the response to add it: public static IEnumerable GetControlsOfType(Control.ControlCollection controls) where T : Control – Rashmi Pandit May 15 '09 at 10:38
Oh yep, you're right. It's required since you're doing the cast. I didn't notice that. – Mehrdad Afshari May 15 '09 at 11:03

Cerebrus · Answer 2 · 2009-05-15T09:49:57.320

2

Mehrdad is quite right, but your syntax (even if you are using C# 2.0) is overly complicated.

I find this to be simpler :

foreach (Control c in gpBx.Controls) 
{ 
  if (c is ComboBox) 
  { 
    // Do something.
  }
}

edited May 15 '09 at 09:49

answered May 15 '09 at 09:42

Cerebrus

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Wrong. typeof(c) is always `System.Type` so `typeof(c) is ComboBox` is always false. You should do `c is ComboBox` – Mehrdad Afshari May 15 '09 at 09:44
Ahh, right! My mistake. Have edited my post with the correction. – Cerebrus May 15 '09 at 09:50
Yeah. It's correct now. For the sake of completeness, typeof(c) will fail to compile in C# if `c` is not a type. That is, you can't do typeof on a variable at all. – Mehrdad Afshari May 15 '09 at 09:52
Yes, I was about to inform you that it will not compile because the typeof keyword evaluates the built-in System.Type, not the runtime type. Thanks for the correction! – Cerebrus May 15 '09 at 09:55
I am using GetType().Name because I have a switch case. c is ComboBox is definitely better way of comparing datatype. Thanks – Rashmi Pandit May 15 '09 at 10:13
@Rashmi Pandit: Indeed, I'd suggest rewriting your switch case with a set of `if` statements using `is` or `as` operators. It's the right way of doing it. What you are doing is relying on the name of type instead of the actual type itself. And btw, it might have inferior performance. – Mehrdad Afshari May 15 '09 at 10:24

score 0 · Answer 3 · edited Apr 17 '12 at 15:37

0

foreach (Control items in this.Controls.OfType<GroupBox>())
{
    foreach (ComboBox item in items.Controls.OfType<ComboBox>())
    {
        // your processing goes here
    }
}

edited Apr 17 '12 at 15:37

Sergey Glotov

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answered Apr 17 '12 at 10:04

Sajjad

11

score 0 · Answer 4 · edited Aug 31 '10 at 13:57

0

if (!(grpbxChild is System.Windows.Forms.Combobox)) continue;

// do your processing goes here
grpbxChild.Text += " is GroupBox child";

edited Aug 31 '10 at 13:57

abatishchev

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answered May 15 '09 at 09:38

Chris Richner

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1

This will *not* compile. The precedence of `is` is lower than `!`. As a result, the compiler will first try to apply `!` to GroupBox variable which fails. For more info: http://stackoverflow.com/questions/811614/c-is-keyword-and-checking-for-not – Mehrdad Afshari May 15 '09 at 10:10
yes, you're right with that, my fault should be if (!(grpbxChild is System.Windows.Forms.Combobox)) – Chris Richner May 15 '09 at 14:05

score 0 · Answer 5 · edited Aug 31 '10 at 13:56

0

foreach (System.Windows.Forms.Control grpbxChild in this.gpbx.Controls)
{
    if (grpbxChild is ComboBox)
    {
        // Process here
    }
}

edited Aug 31 '10 at 13:56

abatishchev

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answered May 15 '09 at 11:28

Looping through controls

5 Answers5