Dynamically create text inputs (ASP.net/C#)

Question

I have an input field on my page where the user will type in the number of text inputs they want to create. The action for the button is:

int num_flds = int.Parse(a_fld.Text);
for (int i = 0; i < num_flds; i++)
{
    TextBox tmp = new TextBox();
    tmp.ID = "answer_box" + i;
    tmp.Width = Unit.Pixel(300);
    answer_inputs.Controls.Add(tmp);
}

Now, I have another button that the user would click after they have filled in all their dynamically-created text boxes. Questions, first of all, am I creating the text boxes dynamically in the correct place? How would I get the values out of the dynamically-created text boxes? (The dynamically-created text boxes are being added to the Panel "answer_inputs".

BobbyShaftoe · Accepted Answer · 2009-01-11 21:28:17Z

2

I recommend reading this and a few other articles about the topic of dynamically created controls. It is not quite as straightforward as you might think. There are some important page lifecycle issues to consider.

answered Jan 11, 2009 at 21:28

BobbyShaftoe

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Øyvind Skaar · Accepted Answer · 2009-01-11 21:51:51Z

When creating web controls dynamically, I find it best to have the controls themselves report in the answers. You can achieve it like this:

Create something in your Page class to store the values:

private readonly Dictionary<TextBox, string> values=new Dictionary<TextBox, string>();

Make a method to act as a callback for the textboxes when their value changes:

void tmp_TextChanged(object sender, EventArgs e)
    {
        TextBox txt = sender as TextBox;
        if(txt!=null)
        {
            values.Add(txt,txt.Text);
        }
    }

And then add this method to each textbox as they are added:

int num_flds;
    if(!int.TryParse(a_fld.Text,out num_flds))
    {
        num_flds = 0;
    }
    for (int i = 0; i < num_flds; i++)
    {
            TextBox tmp = new TextBox();
            tmp.ID = "answer_box" + i;
            tmp.Width = Unit.Pixel(300);
            answer_inputs.Controls.Add(tmp);
            tmp.TextChanged += tmp_TextChanged;
    }

Finally, you iterate through the dictionary on callback to see if it holds any values. Do this in the OnPreRender method for instance.

Edit: There is a problem with this, if the number of text fields are decreased on postback. Some safe way to recreate the previous textfields on postback should be employed.

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