Modal Forms

[ormsk]

I am new to Delphi and I am looking for a way to pass a string from a modal form, back to it's calling form while keeping things encapsulated.

The help files were suggesting using pointers and constructors, but I could not really understand the code that was listed and my small app would not compile.

Can ayone help?

Thanks

 

[hilfy]

What I do when I need this type of functionality is use a "Class Function". This is a special type of method that is part of a particular class that you can call without already having an instance of the class. You declare it like this in either the public or protected section of the interface:

class function ShowMyForm(aOwner: TComponent): String;

The function itself will look something like this:

class function TMyForm.ShowMyForm(aOwner: TComponent): String;
var
  frm: TMyForm;
begin
  frm := TMyForm.Create(aOwner);
  result := '';
  try
    if frm.ShowModal = mrOK then
      result := frm.ReturnValue;
  finally
    frm.Free;
  end;
end;

The code that calls this function will look like this:

  s := TMyForm.ShowMyForm(self);
  if s <> '' then
    //modalresult was mrOK, do whatever you need to 
    //with the return string
  else
    //modalresult was not mrOK, do whatever exception
    //handling you need.

-Dell

 

[Zathras]

The way I do it is to declare a global function in the unit that defines the form you want to show modal. In your case it would look something like this:

function GetMyString(var MyString:string):boolean;

And the implementation would look something like this:

function GetMyString(var MyString:string):boolean;
var
  nModalResult: integer;
begin
  Application.CreateForm(TForm1, Form1);
  With Form1 do
    begin
      SetupDialog();
      nModalResult := ShowModal;
      if nModalResult = mrOk then
        begin
          Result := True;
          MyString := FMyString;
        end
      else
        Result := False;
      Free;
    end;
end;

Notes:
1. Do not auto-create the form.
2. You may not need a SetupDialog() function if there is nothing special to do before showing the form.
3. FMyString is a private variable in TForm1. Put the string you want to return there.

Then to use it simply invoke the global function:

:
:
var
  s:string;
begin
  if GetMyString( s ) then
    begin
      // Use the string
    end;
:
:

 

[Zathras]

Another way for a simple case is to use one of the Delphi functions InputBox or InputQuery.