Solution needed for adding a combobox dynamically and creating events on them?

Question

0.00/5 (No votes)

See more:

Hi team,
below is my code for adding 2 combo-boxes in my c# winform on a button's click event:

C#

private void button1_Click(object sender, EventArgs e)
        {
           // creatXtraCombo();
            ComboBox cmb1 = new ComboBox();
            ComboBox cmb2 = new ComboBox();
            //Button bt1 = new Button();
            //bt1.Text = "More ?";
            //bt1.Click = new EventHandler(bt1_click);
            cmb1.Size = new System.Drawing.Size(200, 21);
            cmb2.Size = new System.Drawing.Size(200, 21);

            cmb1.Location = new Point(cmbAccessories.Location.X, cmbAccessories.Location.Y + 25);
            cmb2.Location = new Point(cmbAccessories.Location.X, cmbAccessories.Location.Y + 50);
            cmb1.BackColor = Color.Pink;
            cmb2.BackColor = Color.Pink;
            cmb1.Text = "Please Select Accessories if Any";
            cmb2.Text = "Please Select Accessories if Any";


            Program.connect2server();
            MySqlCommand cmd6 = new MySqlCommand("select * from accessories", Program.con);
            MySqlDataReader dr6 = cmd6.ExecuteReader();
            while (dr6.Read())
            {
                cmb1.Items.Add(dr6[1].ToString());
                cmb2.Items.Add(dr6[1].ToString());
            }
            Program.con.Close();

            cmb1.SelectedIndexChanged += new EventHandler(cmb1_SelectedIndexChanged);
            groupBox3.Controls.Add(cmb1);
            cmb2.SelectedIndexChanged += new EventHandler(cmb2_SelectedIndexChanged);
            groupBox3.Controls.Add(cmb2);
            //groupBox3.Controls.Add(bt1);
            button1.Visible = false;

        }

and this is my dynamic event for combo-box i.e

C#

cmb1

which i have used as object above.

C#

private void cmb1_SelectedIndexChanged(object sender, EventArgs e)
        {
            MessageBox.Show(cmb1.Text);
        }

my problem is whenever i select any value from combo-box cmb1 i should get its value in messagebox but it is showing error saying:

C#

The name 'cmb1' does not exist in the current context

please help me in this regard and wish you happy new year to all coders here.

Posted 30-Dec-14 1:42am

Dinesh92

Add a Solution

Comments

dev_assault 30-Dec-14 7:48am

declare your combo boxes globally.....otherwise you are doin it correct

like
class A
{
here you declare and create the events in some method or in the constructor and release the events when no object references them
}

OriginalGriff 30-Dec-14 8:00am

No. There is no need to, and particularly when you create them in a button click handler: if you "globalize" them to the form, then what happens when the user presses the button twice?

dev_assault 30-Dec-14 8:58am

i feel nothing would happen, i mean that seems to be the solution......or please enlighten me with a better approach...

OriginalGriff 30-Dec-14 9:48am

Think about it: the first time you click it, you get a combobox, store it in the class level variable, and the event handler works.
Then the user presses it again. You add a second combobox (so the user can now see two) and store it in the class level variable - overwriting the first combo. When the SelectIndexChanged event happens, you don't know if it came from the first or second combobox, and you can't access the first one via the class level variable.

So how do you get at the "right" combobox?

The solution is to not use a class level "global" variable, but to use the sender argument of the event handler method - which contains the instance of the control which raised the event.

dev_assault 31-Dec-14 1:18am

what i meant , is that u make cmb1 global.....which means u declare the those combo boxes at class level or global or whatever.....

dev_assault 31-Dec-14 1:19am

i think i should have explained a bit more...my bad i get it

dev_assault 31-Dec-14 1:19am

but man i have clearly mentioned in my comment

OriginalGriff 31-Dec-14 3:52am

The problem is that since the OP wants to create them dynamically at run time, you still can't do it - that's the same as adding the control via the designer!

[no name] 30-Dec-14 7:51am

sorry i didn't get you would you please explain a little more?

[no name] 30-Dec-14 7:54am

Ok sir,I got...I solved it...Thank you and Happy New Year :)

2 solutions

Solution 2

Change your handler:

C#

private void cmb1_SelectedIndexChanged(object sender, EventArgs e)
        {
        ComboBox cmb = sender as ComboBox;
        if (cmb != null)
            {
            MessageBox.Show(cmb.Text);
            }
        }

The variable cmb1 is local to the button click handler, and goes out of scope at the end of the method.
The sender parameter is always the class instance that signalled the event - in this case the combobox.

Posted 30-Dec-14 1:59am

OriginalGriff

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

BillWoodruff · Accepted Answer · 2014-12-30T01:56:00

The problem is that you declare the variables 'cmb1 and'cmb2 inside the scope (context) of a method, the Button Click EventHandler; outside of that method, therefore, the instances of the ComboBoxes you created do not exist (well, they exist, in a way, until they are garbage collected automatically).

Just move the declaration of your ComboBoxes out of the method, and place them in the scope (context) of the Form:

C#

ComboBox cmb1 = new ComboBox();
ComboBox cmb2 = new ComboBox();

private void button1_Click(object sender, EventArgs e)
{
    // ...
}