Difference between revisions of "Testing, if form exists"
From Free Pascal wiki
Jump to navigationJump to search (I think you meant forum discussions ;) Thanks for the page!) |
m (Fixed syntax highlighting) |
||
(17 intermediate revisions by 7 users not shown) | |||
Line 1: | Line 1: | ||
− | + | {{Testing, if form exists}} | |
− | + | Sometimes a [[TForm|form]] may be launched from several places in a program. If it already exists, it only needs to be brought to the front. If not, it needs to be created. | |
− | + | This method is only needed if the form is not [[Form_Tutorial#Create_a_Lazarus_designed_form_dynamically | auto created]] (ie not listed under Project|Project Options|Forms|Available forms). | |
− | + | The easiest way is: | |
− | + | <syntaxhighlight lang=pascal> | |
+ | if (MyForm = nil) then Application.CreateForm(TMyForm, MyForm); | ||
+ | MyForm.Show; | ||
+ | </syntaxhighlight> | ||
+ | |||
+ | Use <code>CloseAction := caFree</code> in the form's OnClose event, like so: | ||
− | <syntaxhighlight> | + | <syntaxhighlight lang=pascal> |
− | + | procedure TMyForm.FormClose(Sender: Tobject; var Closeaction: Tcloseaction); | |
− | var | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
begin | begin | ||
− | + | CloseAction := caFree; | |
− | MyForm | + | MyForm := nil; |
− | + | End; | |
</syntaxhighlight> | </syntaxhighlight> | ||
− | + | This method is taken from forum discussions. | |
− | + | {{Warning|This method has some limitations: | |
− | + | <br/><br/> | |
− | + | *'''Not''' ''more than one instance'' of that form class should exist at any time. | |
+ | *Reference to any created form of that class should be stored in ''a single global'' variable. | ||
+ | }} |
Latest revision as of 10:10, 29 February 2020
│
Deutsch (de) │
English (en) │
français (fr) │
Sometimes a form may be launched from several places in a program. If it already exists, it only needs to be brought to the front. If not, it needs to be created.
This method is only needed if the form is not auto created (ie not listed under Project|Project Options|Forms|Available forms).
The easiest way is:
if (MyForm = nil) then Application.CreateForm(TMyForm, MyForm);
MyForm.Show;
Use CloseAction := caFree
in the form's OnClose event, like so:
procedure TMyForm.FormClose(Sender: Tobject; var Closeaction: Tcloseaction);
begin
CloseAction := caFree;
MyForm := nil;
End;
This method is taken from forum discussions.