Multiple forms application using one data object across each form

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C#

C#4.0

I have got a class that when created, I need to have another object passed to it.
I have got an application with multiple forms. I have a base form from which all other forms are created and destroyed as need be during runtime... At the moment, my code is clumsy as I used a 'DataObject' with all its internal variables declared as static so that with all the copies of the same object I have in each form, the same data would be used. I know very well that this is NOT good programming but this seems to be a temporary solution around my problem of trying to use the same 'DataObject' in each form. Here is an abbreviated copy of my suggested code that I am trying to use:

public class FormA //which would in reality be a form requiring an object containing data for displaying and modifying
{
    CustomDataClass DataObject;    
    public FormA(CustomDataClass MyCustomCreatedObject)
    {
        DataObject = MyCustomCreatedObject;
    }
    //with all other code related to the form...
}
 
public class FormB //which would in reality be a form requiring an object containing data for displaying and modifying
{
    CustomDataClass DataObject;    
    public FormB(CustomDataClass MyCustomCreatedObject)
    {
        DataObject = MyCustomCreatedObject;
    }
    //with all other code related to the form...
}
//...
//However many forms I will be using...
//...

public class MainForm
{
    CustomDataClass ApplicationData = new CustomDataClass();
    //some code for populating the ApplicationData object with data etc...
    FormA FirstAdditionalForm = new FormA(ApplicationData);
    FormB SecondAdditionalForm = new FormB(ApplicationData);
    //until the number of required forms has been reached...
    
    //on a certain button click method in the MainForm:
    FirstAdditionalForm.ShowDalog();
    //User does what is needed on the form and closes it...
    
    //on a certain button click method in the MainForm:
    SecondAdditionalForm.ShowDalog();
    //User does what is needed on the form and closes it...
}

My Problem:
This does not seem to work when I try to create the two forms from their respective classes. I am not able to pass the 'ApplicationData' object in as a parameter into their constructors and if I do, I have build/compile errors etc.

Where am I going wrong or what is a better way of creating a new form class and passing a data object to it as a ref? This is for a multiple forms application needing data to be transferred between forms using the same data object. I hope this clarifies my problem. Please help...