C#, Object reference for nonstatic field

Question

I have COM server application which controls another application CANoe. I want to show a progress bar on Form2 of COM application. The value of progress bar should be updated in the EventHandler. The eventHandler calls a method of form2 which will update the value of progress bar. The EventHandler is in main form.

private void mCANoeProgProgressChangedInternal(string sysvarName, object Value) // in main Form
{
    if (mCANoeMeasurement != null && mCANoeMeasurement.Running)
    {
        ProgressBarForm.Prog_progress(Value);
    }
}

And in Form 2 -

public void Prog_progress(object value)
{
    progressBarProg.Value = (int)value;
}

it is showing an error

"An object reference required for the non-static field, method or property 'Form2.Prog_progress(object)'" at - ProgressBarForm.Prog_progress(Value); in main form.

Please provide your comments.

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Miq · Answer 1 · 2018-04-05T08:42:45.113

1

In form 1 you need to execute Prog_progress method on an instance of Form2, not on the class (in a static way).

In Form1:

private ProgressBarForm _progressForm = new ProgressBarForm();
(...)
private void mCANoeProgProgressChangedInternal(string sysvarName, object Value) // in main Form
{
     if (mCANoeMeasurement != null && mCANoeMeasurement.Running)
     {
         _progressForm.Prog_progress(Value);
     }
}

edited Apr 05 '18 at 08:42

answered Apr 05 '18 at 07:28

Miq

3,931
2
18
32

Thanks! It resolved the issue. – A.BHi Apr 05 '18 at 08:55

score 0 · Answer 2 · answered Apr 05 '18 at 08:03

0

Probably you are missing instantiating the Form2,

// This is for your parent Form1

public partial class Form1 : Form
{ 
    private void mCANoeProgProgressChangedInternal(object sender, EventArgs e)
    {
        ProgressBarForm frm = new ProgressBarForm(); 
        frm.DoSomething(value);
    }
}

answered Apr 05 '18 at 08:03

CodingLearner

29
6

Instantiating a new form every time something changed would lead you to swamping your memory with unnecessary, duplicated objects. – Miq Apr 05 '18 at 08:28
Agreed. Better to use singleton pattern perhaps to keep it checked – CodingLearner Apr 05 '18 at 08:37
Singleton might be too much, field or property in the parent class would be sufficient. Nevertheless, living object is needed :) – Miq Apr 05 '18 at 08:40

C#, Object reference for nonstatic field

2 Answers2