Question

I got an object, which is called in my form1-window. How can I change anything from the form1-object from within this object, for example a label or a processbar?

Answer 1

It would be a bad (circular) design to give your object a reference to your form. Use an interface or a delegate (callback).

// untested code class MyObjectClass {    public delegate void Reportback(int percentage);     public void DoSomething(Reportback callBack) { ...; callback(i*100F/total); ...} }   class Form1: Form {    private void reportProgress(int percent) { ...; progressbar1.value = percent; }     void SomeMethod() {  myObject1.DoSomething(reportprogress); } }