Expanding the functionality of existing example - delphi

Question

This is just for learning sake : Using accepted answer in this example Delphi application with login / logout - how to implement?,how can you show a specific form (if you have many forms) ?
I have placed a query on that LoginForm (which displays various forms that can be selected and shown).
How should I change the existing code so I can accomplish this maintaining the same functionality meaning that whatever form I select and click 'open' it will become the mainform and be shown?

Answer 1

The main form is the first form created using Application.CreateForm. So use an if or case statement to conditionally switch which form is created that way.
In pseudo-code:
if Form1 is main form then
Application.CreateForm(TForm1, Form1)
else if Form2 is main form then
Application.CreateForm(TForm2, Form2)
....
There are quite likely slicker ways to do this, but this is the basic principle.
So, you might well make a function to return the class of the main form, using whatever mechanism you have to choose it:
function GetMainFormClass: TFormClass;
begin
Result :=...; // your logic here
end;
Then in the .dpr file you write
Application.CreateForm(GetMainFormClass, MainForm);
You seem, to be really struggling with this. I'll try to spell it out in a little more detail. The implementation of GetMainFormClass might look like this:
function GetMainFormClass: TFormClass;
var
FormClassName: string;
begin
FormClassName := ...; // somehow get the name of the form class, e.g. 'TForm1'
if FormClassName = 'TForm1' then
Result := TForm1
else if FormClassName = 'TForm2' then
Result := TForm2
else
raise EUnrecognisedFormClassName.Create(...);
end;
Personally, I don't understand why you are presenting a grid control to the user. To me that seems like a very weak user interface with which to make a selection. I would present a radio group. Then you could write code like this:
type
TMainFormType = (mftForm1, mftForm2, mftForm3);
const
MainFormClass = array [TMainFormType] of TFormClass = (
TForm1,
TForm2,
TForm3
);
Then you can have a function that returns TMainFormType, by way of showing the user a form and presenting a radio group with three buttons. You can convert the radio group's ItemIndex into the appropriate TMainFormType value.
function GetMainFormType: TMainFormType;
begin
// ... your UI shows now, presenting the radio group
Result := TMainFormType(RadioGroup.ItemIndex);
end;
And then in the .dpr file you write
Application.CreateForm(MainFormClass[GetMainFormType], MainForm);
There are lots of different ways to do this, but you do need to understand the basics of branching code. Either if statements, or lookup tables. If you don't understand how these work then, with all due respect, you need to brush up those skills before you proceed.