Changing text box from another class

Question

I'm trying to change value of a text box located in

public partial class Form1 : Form

from another class. I've tried something like this

public void echo(string text)
{
    this.textBox1.AppendText(text + Environment.NewLine);
}

From another class I'm calling it like

Form1 cout = new Form1();
cout.echo("Does this work?");

And I get blank output. I also tried to add the static keyword to the echo method, but I got the same result. I searched over Stack Overflow and didn't get any solution to work. And one thing that triggers me, if I add cout.Show() the same form pop out with valid textBox1 content. Why is that?

Why it is not showing content right away? And how do I fix this?

Solution 1

Each time you say new Form1(), you are creating a distinct and separate instance of that form. Instead, you need to create a variable in the class that you are trying to access your form. For example, let's pass it in the constructor:

public class MyClass {
    public Form1 MyForm;

    public MyClass(Form1 form){
        this.MyForm = form;
    }

    public void echo(string text) {
        this.MyForm.textBox1.AppendText(text + Environment.NewLine);            
    }

}

Notice that you access the particular instance of Form1 in your echo method:

public void echo(string text) {
     this.MyForm.textBox1.AppendText(text + Environment.NewLine);
}

Solution 2

The problem is here:

Form1 cout = new Form1() ;
cout.echo("Does this work?");

You're creating a new version of your main form, Form1.

What is this other class, and how is it being instantiated?

You have two options:

1. When your code in Form1 creates the class, give him an instance to this, and call your echo method on that reference to (the only) instance of Form1.

2. Add an event to this other class, that is fired when he wants to provide some information. Your Form1 code will register an event handler on this event, and make the call to echo himself, when the event fires.

Solution 3

You don't need to create another object of Form1.

Try this code and I think, you will guess what is happening:

Form1 cout = new Form1();
cout.Show();
cout.echo("Does this work?");

Solution 4

Instead of cout try using MessageBox.Show("Does this work?");

Now sending textbox value from one form to another.

protected void btnNext_Click(object sender, EventArgs e)
{
  MyForm2 x = new MyForm2();
  x.Query = "My Query";   // here "Query" is your custom public string variable on form2
  x.Show()
}

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Comments

[Dejano]

Aham, got that. All of you guys gave me right answer and explanation why is this happening, but since nFreeze wrote solution to this I'll mark his answer as correct. Thank you all!

[Hadron]

You must also change "modifiers" to "Public" for the textbox.

[SendETHToThisAddress]

I was able to use internal, but I had to make the method static.