When designing a TForm, a line is added to the form's unit declaring the form object...
var
frmMyForm: TfrmMyForm;
I don't need this form auto-created, and I intend to create multiple instances of it, and to make sure I don't make the mistake of using this declared form, I commented it out...
//var
//frmMyForm: TfrmMyForm;
I was wondering if this is safe to do? I don't see any problems, and the form designer still works fine. But could there be some trouble if I leave this out completely?
This is a very common scenario when using form inheritance. You normally don't want to instantiate derived forms from the middle of the inheritance chain.
The only place where these form variables are used (besides your code perhaps) is the dpr file and that only when the form is autocreated.
So, no problem to remove the declaration.
Related
I'm using Delphi 7 (I know it's antique) and am a bit confused by a form I'm creating as needed and destroying when done with it.
From my main form I create another form requesting a Username and Password. The newly created form properties etc are contained in a another unit and is included in the Uses clause.
In my main form I previously "had" the following code;
var
MyOtherForm: TMyotherform;
Begin
MyOtherForm := TMyotherform.create(Nil);
{ Then I do stuff - blah blah }
MyOtherForm.free;
End;
My question is, when I remove the declaration for MyOtherForm in my main unit it still works without error. For example;
{ var // removed
MyOtherForm: TMyotherform; // removed }
Begin
MyOtherForm := TMyotherform.create(Nil);
{ Then I do stuff }
MyOtherForm.free;
End;
The same result, the form is created as usual and destroyed. What I cannot understand is why. Have I been doing it wrong in the past by declaring my form in the main unit, or does having it declared in a separate unit sufficient?
By default, Delphi creates a global variable for the form. It is added just below the class declaration of the form.
The name for that variable is the class name minus the 'T', so it's the same name you used for your local variable, which is why the code still works: you just stored a new reference in that global variable.
If you have an auto-create form, Delphi will create an instance of the form on start-up of the application, and store the reference in that global. You can manage auto-created forms and data modules in the project options, or you can simply edit the dpr file, in which you will find a line like:
Application.CreateForm(TMyotherform, Myotherform);
But even if your form is not auto-created, Delphi still adds that global variable.
Personally, I don't like those global variables at all, and I always remove them manually when I create a form or a data module. Unfortunately, there doesn't seem to be a possibility to configure this.
So: Remove the global and declare the local variable like you did in your original code. That is the right way to do it. The global is there to make it easier for beginners, but it's not helping the maintainability of your application.
I've had this long time problem that I can't view as text the main form for a project I inherited. Even if no other forms are open.
How can I debug the cause of this error message? What options do I have to fix it?
I found one related newsgroup post http://embarcadero.newsgroups.archived.at/public.delphi.ide/200906/0906193960.html but this only addresses the form inheritance cause, and doesn't explain anything about linked modules. I don't believe I'm using form inheritance.
I do have a DM (data module) for the project, and the form does load a couple of images from the dm through properties of a TTreeView on the form--does having a data module automatically mean I can never view as text a form in Delphi (aside from viewing the form as text in notepad)? It doesn't seem to matter whether my DM is open or closed in the IDE.
I also found one SO question with a related title (Module %s has open descendants or linked modules. can not reload) but the question itself and it's answer is not particularly relevant.
This is sometimes caused by a form that inherits from another form in your project (or the gallery) (known as Visual Form Inheritance in the documentation, IIRC). The IDE doesn't know how to find the base class for the form; it needs that opened before the descendant form. For instance, this can cause the same error if the unit containing TMyBaseForm isn't opened first in the IDE, particularly if the base (ancestor) unit is not included in the project first:
unit SpecialForm;
interface
uses
Forms, { all the other usual stuff }, BaseForm;
type
TMySpecialForm = class(TMyBaseForm)
private
public
end;
You can tell if this is the case by looking at your form's class declaration - if it descends from anything other than TForm, this is probably the cause of the error.
(Another instance of it happening is often when using a datamodule, because the base TDataModule .DFM isn't available. Attempting to view the datamodule .DFM as text will cause this error every time; the solution is to close your project and use an external editor such as Notepad or Notepad++ to edit the .dfm for your datamodule.)
I've had this issue occasionally, perhaps when I've used Frames, but my latest instance didn't involve Frames nor Data Modules nor inherited forms.
After an enormous amount of work creating a copy of the form (which copy didn't have the problem) and renaming the original unit and the form itself (which initially seemed to solve the problem), it turned out to be a live binding between forms.
Specifically, in my FMX application Form A has an options page with a TSpinBox that allows the user to set the minimum value for a TTrackBar on Form B (which was the form giving me grief). So the TSpinBox.Value was set to update the TTrackBar.Min field by means of a live binding. Closing Form A, or removing that live binding (and replacing it with an event handler to do the same thing) solved the problem.
I'd like to call upon the answer of Phillip J. Rayment and ADD that you don't have to have live binding to have this problem occur. It's sufficient to have custom control (class) of which you have an instance in another form. Then the RLink32 problem can appear and won't be solved until you close the form where you have the instance. The problem I experienced gave the following messages:
-RLink32 (during building)
-Access violation in module designide160.bpl` (if I made a modification to the problematic form)
-The module has open descendants or linked modules” error (if I tried to 'View as Form')
Is it possible to override the class file location of a framework class via classmap and autoloader? If yes, then how?
Example: I want to override Zend\Form\Fieldset, so that everywhere in the framework where Zend\Form\Fieldset is referenced, I want it to use my own class file instead of the original.
Motivation: When updating the framework, I want to keep my modifications safe from getting overwritten.
Known alternative: Modify the code in the framework.
Disadvantage: Modification gets lost when updating the framework.
writing the same class (FQCN) at another location is generally a bad idea. This causes two classes which are equally named to live in two separate locations. It's a much better idea to create your own Fielset in your own namespace. Say, Application\Form\Fieldset.
You can extend the ZF2 fieldset by your own. Then reference this new fieldset class and its all much more maintainable.
The downside of this method is you don't automatically use the new fieldset class. You have to reference the Application\Form namespace in every form you use. On the other hand, this makes it much more clear to other users of you code what exactly happens: there are no unexpected consequences using ZF2 code.
The only remark I have to make here is, for what do you need another fieldset? If you think you need that for view helpers, that's not true. You can modify the view helper to render fieldsets without modifying the Fieldset form class itself.
1- Why is it necessary to name the methods of a class in a dwsunit this way?
dwsUnitClasses'ClassName''MethodName'Eval(Info: TProgramInfo;
var ExtObject: TObject)
2- Is there a link that must be done between the method defined in a dwsunit and its code?
coz it is not working with me. I took the demo attached with the DWscript (Custom Classes) and made something that looks like it but it is just not functioning.
No it's not necessary, that's just the format the IDE uses for auto-generated event names.
Usually you define script classes, their methods in the structure view, then you double-click their OnEval (or other) event in the properties editor, the IDE will create a method with a name like the above and you can implement there.
If you declare the methods manually, then you also have to attach their events manually, but it's not different than what you end up doing for a button click event (and where you end up with a Button1Click method).
Apart from the implementation code itself, most of the declarations in DWScript can happen at design-time, and are stored in the DFM. The Structure View is convenient for that, but you can also use the property editor only (it was even more convenient in older Delphi versions, when the structure view was sticking to design-time structures, rather than being reused for source structure).
I have a utility routine that I call when validating user input in a dialog fails. It sets focus to the offending control, beeps and displays an appropriate message to the user. This works well as long as the offending control is not hidden. Now I have to adapt this to a situation where the relevant controls are children of some kind of collapsible group boxes (possibly even nested), and I have to make sure that the "ancestor" boxes are expanded before calling SetFocus.
Now I have a few possibilities:
Build knowledge about the collapsible component into the error reporting routine. I'd like to avoid that as the routine should rather stay generic.
Pass an callback that can be called prior to (or instead of) SetFocus. This is error prone because one has to remember to pass the callback at all the relevant places.
My favourite solution would probably be an event (or overrideable method) (probably in TWinControl) that tells a container control "please make sure you and you child controls are visible" but I don't know of such a thing.
Any ideas how I can handle this situation?
Define an interface with a method called something like: EnsureVisible.
Implement it for all your components (you may need to derive your own versions of some of these components). This allows different controls to have quite different behaviour.
When a control needs to make sure it is visible it walks its parents and calls EnsureVisible if the interface is implemented.
If you don't like interfaces then do it with a custom Windows message, but you get the basic idea.
In my opinion the best solution would be a separate routine that builds knowledge about all container controls, allowing the dialog validation routine to stay generic and at the same time being focused enough to be easily tested and maintained. Something along the lines of:
procedure ForceControlVisible(C: TControl);
begin
// Recursive code
if Assigned(C.Parent) then ForceControlVisible(C.Parent);
// Code specific to each container control class
if C is TTabSheet then
begin
// Code that makes sure "C" is the active page in the PageControl
// goes here. We already know the PageControl itself is visible because
// of the recursive call.
end
else if C is TYourCollapsibleBox then
begin
// Code that handles your specific collapsible boxes goes here
end
end;
OOP-style methods that rely on virtual methods or implementing interfaces would be way more elegant, but require access to the source code of all the controls you want to use: even if you do have access to all required sources, it's preferable not to introduce any changes because it makes upgrading those controls difficult (you'd have to re-introduce your changes after getting the new files from the supplier).
Each component knows its Parent. You can walk up the list to make each parent visible.