How do I fix this error

Question

1.00/5 (3 votes)

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C#

using System;
using System.Threading.Tasks;
using System.Windows.Forms;
using TelegramBotSharp;
using TelegramBotSharp.Types;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public static TelegramBot bot;
        public Form1()
        {
            InitializeComponent();
        }

        private  void button1_Click(object sender, EventArgs e)
        {
            bot = new TelegramBot("146900545:*****************-gUjWMwZ7-FyoSPg");
            new Task(PollMessages).Start();

        }

         async void PollMessages()
        {
            while (true)
            {
                var result = await bot.GetMessages();
                foreach (TelegramBotSharp.Types.Message m in result)
                {
                    if (m.Text == null) return;
                    MessageTarget target = (MessageTarget)m.Chat ?? m.From;
                    bot.SendMessage(target, m.Text);
////////this error///////////////////////
                    label1.Text =m.Text;
/////////////////////////////////////////
                }

            }
        }

    }

}

What I have tried:

i canot do this ( label1.Text =m.Text; )

Posted 25-Apr-16 22:56pm

vahidsj2

Updated 25-Apr-16 23:31pm

v2

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Comments

Jochen Arndt 26-Apr-16 5:03am

What is label1 (it is nowhere defined in your code snippet)?

What is the exact error message?

vahidsj2 26-Apr-16 5:09am

it is a user control that i added it from tool box
it can be any user control

Jochen Arndt 26-Apr-16 5:23am

Use the Reply button right of a name to answer to a comment. Then the poster will get an email notification. So I saw your answer just by chance.

I had a look at your code and did not saw any definition for 'label1'. The compiler is doing something similar:
It will search for the definition and throw an error if there is none.

Therefore, I asked for the exact error message. It will help to find the problem.

phil.o 26-Apr-16 6:08am

You are stating there is an error but you do not indicate what is the error message. How are we supposed to deal with that?

2 solutions

Solution 2

First check the control you name exists. If it doesn't, it'll be underlined in red and you'll get an error: "The name 'label1' does exist in the current context"
Make sure you added the control to the right Form, and that it's name has not been changed via the Properties Pane.

But even when you fix that, it won't work: you are setting the value of a string from within a loop - so it will only ever show the last string you assign. If you want to show multiple strings, then try this:

C#

StringBuilder sb = new StringBuilder();
foreach (TelegramBotSharp.Types.Message m in result)
    {
    if (m.Text == null) return;
    MessageTarget target = (MessageTarget)m.Chat ?? m.From;
    bot.SendMessage(target, m.Text);
    sb.AppendLine(m.Text);
    }
label1.Text = sb.ToString();

But even when you fix that...it won't work, because you are trying to access a UI control from a different thread from that which you created it on - and that's not allowed.
Instead, you have to Invoke it: Control.Invoke Method (Delegate) (System.Windows.Forms)[^]
I'd be tempted to suggest that you might be better off using a BackgroundWorker and passing messages to display via the ProgressChanged event and displaying them in your UI thread directly.

Posted 25-Apr-16 23:31pm

OriginalGriff

Comments

BillWoodruff 26-Apr-16 23:10pm

+5

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Sascha Lefèvre · Accepted Answer · 2016-04-25T23:21:00

Solution 1

Controls can only be manipulated by the UI thread. If you want to change something about a control from a different thread then you have to invoke the action that should be performed on the control on the UI thread:

C#

label1.Invoke((Action)(() => { label1.Text = m.Text; }));

Posted 25-Apr-16 23:21pm

Sascha Lefèvre

Comments

Sergey Alexandrovich Kryukov 26-Apr-16 10:46am

5ed.
—SA

Sascha Lefèvre 26-Apr-16 11:17am

Thank you, Sergey.

BillWoodruff 26-Apr-16 23:09pm

+5

Sascha Lefèvre 27-Apr-16 7:10am

Thank you, Bill!