Changing The Label Text in Button Click - Understanding For Loop

Question

When I clicked button starts for loop from i=0 and I want to see on the label value of i. However I only see last values of i.

public partial class Form1 : Form
    {
        int i;
        public Form1()
        {
            InitializeComponent();
        }

        private void btnclick_Click(object sender, EventArgs e)
        {
            for (  i = 0; i < 3; i++)
            {                
                lblForLoopExample.Text = i.ToString();
                System.Threading.Thread.Sleep(1000);
            }
        }
    }

when I run the my code I only see on the label ; 2 .

I want to see such a like below;

When the started For loop, i = 0, I must see the 0 on the Label.Text. An then when the i = 1, I must see 1 on the label.Text. And when i = 2, I must see 2 on the Label.Text.

I added Thread.Sleep(1000) however, result didn't change.

Where I am make mistake?

Please help me, if you help me , I will appreciate you.

Thanks,

Code is running too fast. Try adding a sleep or wait to see if you can observe it. Thread.Sleep(1000) to sleep for 1 sec :) — Matt Clark, Oct 10 '16 at 20:45
The loop is very quick so you not able to see how the label is updated, this is the reason that you see only the last value which is 2 — mbadeveloper, Oct 10 '16 at 20:45
yes you right. I added thread.sleep(1000); But I saw the last value again — embedded_master, Oct 10 '16 at 21:02

score 1 · Answer 1 · edited Oct 11 '16 at 00:03

1

You need to append the lbl to get all the values. Right now, it finishes the loop and give you the last value in your label

public partial class Form1 : Form
{
    int i;
    public Form1()
    {
        InitializeComponent();
    }

    private void btnclick_Click(object sender, EventArgs e)
    {
        for (  i = 0; i < 3; i++)
        {

            lblForLoopExample.Text + = i.ToString();


        }
    }
}

edited Oct 11 '16 at 00:03

embedded_master

19
1
7

answered Oct 10 '16 at 20:45

Nirjhar Vermani

1,215
8
17

add `i.ToString()` in your loop – mybirthname Oct 10 '16 at 20:46
Nirjhar, yes you right. I added thread.sleep(100); But I saw the last value again. – embedded_master Oct 10 '16 at 21:01
Can you update the question with the output you are looking for. People are answering your question to give you an output of 0,1,2 together on one line and page. – Nirjhar Vermani Oct 10 '16 at 21:13

score 0 · Answer 2 · answered Oct 10 '16 at 20:49

Each loop you re-write the string. Instead of saying

lblForLoopExample.Text = i.ToString();

You need to add to the string on each iteration. I'd create a variable to hold the value, and so something like this:

string myString = string.Empty;

for(i=0;i < 3; i++)
{
    myString += i.ToString() + ", ";
}

lblForLoopExample.Text = myString.substring(0, (myString.length - 1));

substring is just so you don't have that trailing comma. It's kind of dirty code, but it will work.

Raktim Biswas · Answer 3 · 2016-10-10T21:00:32.440

0

First of all, your code won't compile as you are missing the exact format of the ToString() method in i.ToString along with the ;

lblForLoopExample.Text = i.ToString();
                                   ^^^

As per your code, you should try this:

for (  i = 0; i < 3; i++)
{
    lblForLoopExample.Text += i.ToString() + ", ";
}

edited Oct 10 '16 at 21:00

answered Oct 10 '16 at 20:53

Raktim Biswas

4,011
5
27
32

score 0 · Accepted Answer · answered Oct 11 '16 at 12:55

Your problem is that you're doing work on the UI thread while expecting the UI thread to update your form.

While you process your loop, the UI thread is actually executing this code. The UI thread is therefore unable to update the form with the intermediate values you are setting within the loop. Once your code completes, the UI thread is then free to update the form. That's why you see the last value only.

You can see this better if you updated your code to loop ten million times instead of 3. Your form will become unresponsive and will appear locked up. That's because Windows knows your UI thread is locked in an intensive process and is unable to update the UI.

The solution is to use a background thread to run your process and synchronize updates with the UI thread. You'll also have to slow your loop down to see the changes, as others have suggested.

To learn more about how the UI thread works, and how to synchronize background threads with it, read this article (it's about WPF, but it covers the general case).

Changing The Label Text in Button Click - Understanding For Loop

4 Answers4