How to access a visual component from another form in c#

Question

I have a textbox in my main form.

Now I have created a function which is used to set the value of the text box.

public void SetTextOfTextBox(String text)
{
  textbox1.text = text;
}

Now in my main form I call another class (class b) which does some work for me. Now i want to be able to call my setTextofTextBox function from class b.

Now if I try Form1.SetTextOfTextBox("test"); this doesn't work. What am I doing wrong?

How do I access components of a a Form from another class.

Did you create Form instance before you try to access it? Is Form1 variable or Form name? — HABJAN, Jan 15 '14 at 07:08
Well the form is the class which is running. So it calls class b. surely it is already instantiated? — Zapnologica, Jan 15 '14 at 07:09

score 2 · Answer 1 · answered Jan 15 '14 at 07:11

Form1.SetTextOfTextBox("test"); this doesn't work

This doesn't work because SetTextOfTextBox is not static and you cannot access a non-static function directly. And you can't make it static either because your textbox is form level control.

How do I access components of a a Form from another class

You will have to pass the instance of Form1 to your other class to access it. Something like

  Class B = new ClassB(this);  //where this is the instance of Form1.

score 1 · Answer 2 · answered Jan 15 '14 at 07:10

You will need a reference to the instance of Form1 in class b, otherwise you cannot call member methods.

Something like this:

class Form1 : System.Windows.Forms.Form {
    void functionInForm1() {
        ClassB objB = new ClassB();
        objB.doSomething(this);
    }
}

class ClassB {
    void doSomething(Form1 form) {
        form.SetTextOfTextBox("test");
    }   
}

score 0 · Answer 3 · answered Jan 15 '14 at 07:18

0

Find out the Form1 and call the method:

  foreach (var form in Application.OpenForms) {
    Form1 myForm = form as Form1;

    if (!Object.ReferenceEquals(null, myForm)) {
      myForm.SetTextOfTextBox("Test");

      break;
    }
  }

answered Jan 15 '14 at 07:18

Dmitry Bychenko

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score 0 · Answer 4 · answered Jan 15 '14 at 07:31

Did u try using delegates.

Specify the delegates in your ClassB like this.

public delegate void OnDone(string textValue);
public event OnDone OnUserDone;

after completing the task in ClassB call event:

OnUserDone("DoneClassB");

When u create the object of class in form map delegate function.

 Classb b=new Classb();
 b.OnUserDone += new Classb.OnUsrControlDone(CompletedClasss);

Define the function in form like below.

void CompletedClasss(string textValue)
{
            SetTextOfTextBox( textValue);
}

How to access a visual component from another form in c#

4 Answers4

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