Showing MDI form as modal - delphi

Question

This will sound against the nature of MDI.. I need to show a MDI form (FormStyle=fsMdiChild) as modal sometimes. And I also need to access the part between Application.CreateForm and OnShow event of another MDI form, i.e.
Application.CreateForm(Form2,TForm2); // but don't set form2's visible property true.
Form2.caption:='not working example';
Form2.SomeMagicToSetVisibleTrue;
Any ideas?

Answer 1

For your first problem: Add another constructor, for example CreateAsMDI, like this:
constructor TModalAndMDIForm.CreateAsMDI(AOwner: TComponent);
begin
f_blChild := true;
GlobalNameSpace.BeginWrite;
try
inherited CreateNew(AOwner);
if(not(csDesigning in ComponentState)) then begin
Include(FFormState, fsCreating);
try
FormStyle := fsMDIChild;
if(not(InitInheritedComponent(self, TForm))) then
raise Exception.CreateFmt('Can't create %s as MDI child', [ClassName]);
finally
Exclude(FFormState, fsCreating);
end;
end;
finally
GlobalNameSpace.EndWrite;
end;
end;
In the normal constructor just set the variable f_blChild to false and call the inherited create.
You need two more things, rather self explaining:
procedure TModalAndMDIForm.Loaded;
begin
inherited;
if(f_blChild) then
Position := poDefault
else begin
Position := poOwnerFormCenter;
BorderStyle := bsDialog;
end;
end;
//-----------------------------------------------------------------------------
procedure TModalAndMDIForm.DoClose(var Action: TCloseAction);
begin
if(f_blChild) then
Action := caFree;
inherited DoClose(Action);
end;
Now you can call the form modal, if created with the standard constructor, and as MDI child, if created with CreateAsMDI.
If you include this in your form's declaration
property IsChild: boolean read f_blChild;
you can even do things depending on whether the form is an MDI child or not, just interrogating the isChild property.
As for your second problem: do not use Application.CreateForm, but create your form yourself:
Here the two creations for modal and MDI:
//Modal
frmDialog := TMyForm.Create(self);
// Your Code
frmDialog.ShowModal;
frmDialog.Release;
//MDI-Child
frmDialog := TMyForm.CreateChild(self);
// Your code
frmDialog.Show;
I have translated this answer form an article on the site DelphiPraxis.

Answer 2

The simplest method is to create a trivial subclass of the form, and set
FormStyle = fsMDIChild
AND
Form.Visible = False
in the property inspector. This is tried and tested!

Answer 3

At least for Delphi 2007 and 2009 creating the MDI child form invisible is easy. For the early Delphi versions (where it was impossible to set Visible to False in the property inspector) you just have to provide a handler for the OnCreate event and access a protected field of the class:
procedure TMDIChild.FormCreate(Sender: TObject);
begin
FFormState := FFormState - [fsVisible];
end;
This will disable the automatic showing of the MDI child. After you are done with your other initialisations you can simply Show it or set Visible to True.
I will not try to answer your question about modal MDI child forms, as this violates the conventions of the Windows platform.

Answer 4

No answers above actually does the job required. The best answer is wrong as well, because of following:
Opening the first form;
Maximize it;
Now say this form calls another form (mdi);
When it is constructed the same way you will get buggy layout... (it will mdi child, but not maximized, however the first will be still maximized). So a buggy state.
If you really need to decide in run-time whether it's a fsMDIChild or fsNormal you need to apply following approach.
You have form which is stored as fsNormal in design (or vice-versa);
Override the InitializeNewForm method;
Set the value of FFormStyle to fsMDIChild (as shown below).
...
TYourForm = class(TForm)
...
protected
procedure InitializeNewForm; override;
...
procedure TYourForm.InitializeNewForm;
var
FS: ^TFormStyle;
begin
inherited;
if DoYourCheckForMDI then
begin
FS := #FormStyle;
FS^ := fsMDIChild;
end;
end;