Why does my code that adds controls in a loop fail?

Question

public MainPage()
{
    InitializeComponent();
    CheckBox c = new CheckBox();
    for (int i = 0; i < 2; i++)
    {
       c.Content = " Value ";
       lbox.Items.Add(c);
    }
}

lbox is an empty listbox in the UI and the above code throws an unhandled exception which is caught by code in App.xaml.cs. The code works fine if I remove for loop. What's wrong with this code?

guessing lbox can't have the same object twice (a set maybe?) — Roee Gavirel, Jan 02 '13 at 13:44

score 5 · Answer 1 · answered Jan 02 '13 at 13:42

5

You are initializing CheckBox outside the loop once, and adding it twice. Move it inside the for loop.

    for (int i = 0; i < 2; i++)
    {
        CheckBox c = new CheckBox();
        c.Content = " Value " ;
        lbox.Items.Add(c);
    }

answered Jan 02 '13 at 13:42

Tilak

30,108
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It had no text, just code. Makes for a crap answer. It has some words now, so I'll remove the downvote – Kieren Johnstone Jan 02 '13 at 14:24

score 4 · Answer 2 · answered Jan 02 '13 at 13:43

4

Create a new instance of checkbox in the loop

public MainPage()
{
    InitializeComponent();

    for (int i = 0; i < 2; i++)
    {
        CheckBox c = new CheckBox();
        c.Content = " Value " ;
        lbox.Items.Add(c);
    }
}

answered Jan 02 '13 at 13:43

CR41G14

5,464
5
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64

score 3 · Accepted Answer · answered Jan 02 '13 at 13:44

3

try putting the check box inside the loop

public MainPage()
{
    InitializeComponent();

    for (int i = 0; i < 2; i++)
    {
        CheckBox c = new CheckBox();
        c.Content = " Value " ;
        lbox.Items.Add(c);
    }
}

answered Jan 02 '13 at 13:44

iJade

23,144
56
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Reza Alipour Fard · Answer 4 · 2013-01-02T14:11:53.690

1

Bellow code it's OK:

in Form1.Designer.cs you must define:

partial class From1
{   
    private.System.Windows.Forms.ListBox lbos;
    private.System.Windows.Forms.CheckBox c;
}

and in Form1.cs you must write:

public MainPage()
{
    InitializeComponent();

    for (int i = 0; i < 2; i++)
    {
        this.c.Text = " Value " ;
        this.lbox.Items.Add(c);
    }
}

edited Jan 02 '13 at 14:11

answered Jan 02 '13 at 14:05

Reza Alipour Fard

21
2

score 0 · Answer 5 · answered Jan 02 '13 at 13:44

0

public MainPage()
{
    InitializeComponent();
    for (int i = 0; i < 2; i++)
    {
        lbox.Items.Add(new CheckBox{Content =" Value "});
    }
}

answered Jan 02 '13 at 13:44

burning_LEGION

13,246
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Why does my code that adds controls in a loop fail?

5 Answers5