Update textbox from different thread and different class

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I have a problem when updating textbox which is called from different thread.
I have two classes in different .cs files (Form1.cs and Class1.cs).

In Form1.cs, there are button and textbox controls. The flow is simply like this:
1. Click button
2. Create and start new thread

In Class1.cs, the flow is even simpler:
1. Run a function which is writing a text into textbox control of Form1.

Problem:
1. "test" won't print out in textbox.
2. InvokeRequired is always false, have no idea why?

This may be a simple and stupid question but annoying me for a long time, please kindly advice.
Thank you all.

Two cs files are posted as follows:

Form1.cs

C#

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

        private void button1_Click(object sender, EventArgs e)
        {
            Thread th = new Thread(new ThreadStart(Class1.start));
            th.Start();
        }

        public void UpdateTxt(string str)
        {
            if (InvokeRequired)
            {

                this.Invoke(new Action<string>(UpdateTxt), new object[] { str });
                return;
            }
            textBox1.AppendText(str + "\n");
        }
    }
}

Class1.cs

C#

namespace WindowsFormsApplication1
{
    class Class1
    {
        public Form1 fm = new Form1();

        public static void start()
        {
            Form1 fs = new Form1();
            fs.UpdateTxt("test");
        }
    }
}

Posted 4-Jun-13 23:50pm

ongguntur

Updated 4-Jun-13 23:56pm

v2

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2 solutions

Solution 2

Hi lukeer, as you said, I used event and it worked.
Thanks a lot!

Posted 6-Jun-13 19:28pm

ongguntur

Comments

lukeer 7-Jun-13 1:37am

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lukeer · Accepted Answer · 2013-06-05T00:23:00

Solution 1

You're creating new Form1's with every call to Class1.start().
Use the instance instead, that is created in Program.cs in the line

C#

Application.Run(new Form1());

Usually, you would Class1 let fire an event that UpdateText() reacts to.

Posted 5-Jun-13 0:23am

lukeer

Updated 5-Jun-13 0:28am

v2