If one looks at hierarchical structure of html and dfm, he could find similarities (nested structure, properties (attributes) and so on). The next step is to ask is there something like css (Cascade style sheets) in Delphi world. So for example rule like this
TPanel TPanel BorderWidth=2
could define that for any TPanel placed in another panel the property BorderWidth should always be 2.
or
TPanel.MyPanel TLabel Font.Style=[fsBold]
for TPanel named MyPanel any label inside should be bolded (similarly to css The particular name (MyPanel) can be equivalent to id attribute of html)
So is there library/unit that was developed for something like this?
I suppose there should be some challenges
implementing this in design-time can pose some compatibility problems with internal form designer of Delphi (Probably this library can be more run-time oriented)
In html world it is mostly about visual so an error could lead just to visual peculiarities, but in Delphi properties sometimes intended to be set explicitly by the programmer's hand and making it subject of mass management could pose security and stability threats.
Nevertheless, I thought that we are too bound to properties manual changing. Even if it's copy-paste, the root of any property change is a dedicated mouse click.
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I've been tasked with supporting an application that is written in Delphi, which is occasionally crashing with the error message "Control '' has no parent window".
My question is not to understand WHY the error is happening, but to understand why the control has no name assigned.
Is the seeming lack of a name for the control a function of the way the control was coded (i.e., controls can have names but they are optional), or is this because the name of the control is inherited from the (non-existent) parent?
My question is not to understand WHY the error is happening, but to understand why the control has no name assigned.
Controls that are created at runtime, as opposed to design time, need not have names. So, this control has no name because the programmer created it without naming it, or it is a control created internally by another control, without being named.
It is perfectly normal for controls not to be named. It is perfectly reasonable for complex applications never to refer to control names.
There are multiple reasons, including but not necessarily limited to:
1) It wasn't given a name in the code.
2) It doesn't inherit a name for whatever function called it
I created in Lazarus a new component based on TPaintBox. Now in Object Inspector I have all Properties and Events which belong to this base component (TPaintBox).
My question is: can I hide chosen Properties and Events for my component?
For example I would like to leave visible only Width and Height properties.
Can you help me?
Once a property/event has been published, it cannot be un-published.
However, it can be hidden from the Object Inspector, at least (it is still accessible to code).
After your design-time code has registered the component with the IDE, it can then:
in Delphi, call UnlistPublishedProperty() from the DesignIntf unit.
in Lazarus, call RegisterPropertyEditor() from the PropEdits unit to register the THiddenPropertyEditor class for the property/event (see Hide Properties (UnlistPublishedProperty) in the Lazarus forum).
Not sure about Lazarus, but in Delphi TPaintBox is a lightweight descendant of TGraphicControl. The majority of its declaration is just publishing properties. I don't know what your component is doing, but it might be easier to derive it directly from TGraphicControl and duplicate the TPaintBox code wherever it actually is needed. Then you can publish only the properties you want. Note that you still have those properties declared published in TControl and TComponent.
No, you can't hide (unpublish) published properties.
In Delphi most objects are based on a parent classes with all the same properties, but mostly hidden.
So while you can't hide exposed properties you can usually achieve what you want by basing your class on the TCustomxxx instead.
Sadly, TPaintbox is an exception. It is descended from TGraphicControl, but that in turn is descended from TControl which already has a number of published properties, including AlignWithMargins, CustomHint and several others, and that in turn is descended from TComponent which has Name and Tag published. To be fair, you need name for sure, and Tag is not a problem I would think.
If you just had to go back to TGraphicControl, that is not too bad. Just one member and a couple of routines to copy. But to go back to TComponent, which is what you would need to do to hide a number of properties is not really viable.
I would like to add "MyProperty" to TTabSheet and work with it at design time. However if I subclass it I fear I will need to also subclass TPageControl, since it internally creates/manages the TTabSheets.
I believe this would require duplicating the TTabSheet management code to reference TMyTabSheet instead of TTabSheet, since it will need to invoke TMyTabSheet.create. This feels like something I will regret when a new version of Delphi updates TPageControl and I forget to update TMyPageControl.
I am also researching "class helpers" as another option.
Does anyone have advice on how to best accomplish this?
Thanks!
Type Helpers are merely compile-time sugar, they would cause no effect over the already compiled code, that stock VCL is together with TPageControl and TForm. That is a dead-end.
However you have a slight misconception here that TPageControl... internally creates... the TTabSheets. Indeed, when you create the sheets by the means of TPageControl itself, like right-clicking it and selecting "New Tab" that si what happens. But when you create the living form object out of DFM file (or DFM resource in your compiled EXE) that is TForm itself that creates ALL the components, including both page control and its tabsheets.
Just see my answer at How to efficiently let a `ParentFont = False` child control to use same font name as parent? - that would show you how far it is about the owner - TForm, not about TPageControl or other parent components when it comes about selecting specific classes for the actual tabs or other elements..
So you are free to pursue subclassing tabsheets only.
Create the TMyTabsheet = class(TTabSheet) component
Create and install into IDE the design-time package that would introduce new subclassed tab sheet to Delphi Form Editor
In your form put the stock TPageControl and create all the needed tabs regular way
in IDE form Editor right-click over the form free space and in the menu do the "View As Text Alt-F12" command - you would see the text content of your form's DFM file
in those DFM sources find your tab sheets and change their stock TTabSheet class to be your derived sub-class
right-click the text editor and choose "View As Form Alt-F12" command
If all was done correct then Delphi would recreate the form with your new-class sheets now. Find your new properties in Object Inspector and change them.
Now switch to .Pas sources of your form and find the declarations of those tab sheets and change their type too. That is only required if you would have to access your new properties from the Delphi sources. If not you can leave their declaration as TTabSheet in pas-file as your class is direct descendant from it. You may leave those declarations as they were - but then you would have to add RegisterClass(TMyTabSheet); call into the very initialization section at the bottom of your unit, so when the form would construct itself out of the DFM it would be able to find the class implementation by the name. If you would change the declaration (at least one of those) then your form would automagically call all needed RegisterClass before streaming out of DFM. Choose any option you like.
Optionally and later, extend your design-time package to find and hijack IDE Form Editor's right-click menu for TPageControl and add "New My Subclassed Tab" command there. Just to avoid manual post-factum DFM editing. if you would do it often
This feels like something I will regret when a new version of Delphi updates TPageControl
After you created and tuned the form and saved it into DFM - it would be TForm that creates all the components out of the saved DFM-data, and that includes your tabs too. Unless very improbable event EMBT would kill the whole VCL streaming (made back in Delphi 1 in 1995) and redesign it from scratch (killing all the compatibility with existing Delphi sources at once), there should be no problem with forward compatibility with specifying your class in DFM. It is just the standard way VCL is designed - to get specific component types from the DFM.
I've had this problem for years but maybe it is now possible to easilty solve it. I need to lay out a panel with several TEdit controls, each should show, and allow editing of, a published property of a class. Traditionally I would use TEdit (or a numeric derivative from the Raize or Developer Express libraries) and 'wire up' the OnKeyPress and OnExit events, convert between the edit text and the property type etc etc. All as per Delphi 1 (whose big birthday is soon!).
These days we have RTTI and Live Bindings, so ideally I'd like a way of telling a TEdit (or another similar control) about a single published property and the necessary 2-way link would then be established without all the wiring up and conversions. An object inspector does this job of course, but I'd like a more formal custom layout using labelled edit controls. It would be fine to simply cope with integer, float and string, and something like a TDBEdit where the field name was my property name would be great.
I've taken a look at the 'Bind Visually' designer (I have XE3) but I'm on to uncertain ground. Can anyone suggest a means of doing this? Thanks.
The comments above by Ken White and Sir Rufo are good pointers to the use of Live Bindings for wiring up components between each other, but I need to wire up controls to my own object and which is created at runtime. Further digging led me to this excellent article which pretty much does what I want. Jarrod's TBoundObject is intended to be the ancestor for your own objects, but by including an FObject field passed in the constructor and replacing his use of 'Self' by FObject, you can instantiate a standalone 'TObjectBinder' that easily connects various standard controls to published properties.
Three components, working together:
* CompA, a TComponent descendant, a mastermind component knowing many things and tying things together
* CompB, a TComponent descendant, mines some data from it's CompA and crunches it. Can amongst other things feed CompC with data to present
- Has a published property of type CompA
* CompC, a TComponent descendant, a TFrame descendant drawing surface that can be set at designtime to use a CompB as data provider
- Has a published property of type CompA
- Has a published property of type CompB
I think I remember having read, even though I cannot state where, that Delphi's streaming engine reads all components from the .dfm and builds a dependency graph. This graph is then used to create all components in correct order. For the listed components it should be CompA first (since it uses none of the other ones), then the CompB (it uses CompA and must be created after) and lastly the CompC since it has properties of both the other component types.
This does not happen. CompC is created before CompB. If i rearrange the order in the .dfm file using a text editor it works. The property values are not used in any constructors, only in the Loaded procedures. But truly there must be a way to make it work no matter the order of components in the dfm?
I've been banging my head against the wall for two days straight now, I need somebody to tell me which keyword I forgot or what error in design I have.
I suspect your fault is you're trying to access other objects properties on setters for sibling pointers, forgetting that at dfm loading stage --runtime-- you can't be sure pointers to other components your component depends on are yet valid because it is possible that other component is not yet created. This works this way since Delphi 1.
Because of this, you usually deffer the reading of other component's state (for example) to your overridden Loaded method.
When the streaming system loads a form or data module from its form file, it first constructs the form component by calling its constructor, then reads its property values from the form file. After reading all the property values for all the components, the streaming system calls the Loaded methods of each component in the order the components were created. This gives the components a chance to initialize any data that depends on the values of other components or other parts of itself.
Note: All references to sibling components are resolved by the time Loaded is called. Loaded is the first place that sibling pointers can be used after being streamed in.
Because of this, usually on a setter method for a sibling pointer property you usually perform a check of this type:
procedure TMyComponent.SetDataSource(Value: TDataSource);
begin
FDataSource := Value;
//streaming in stage
if not (csLoading in ComponentState) then
ReadDataSourceProperties;
end;
procedure TMyComponent.Loaded;
begin
ReadDataSourceProperties;
end;
Take a look at the VCL source, you'll find hundreds of examples of this.
If your components are that much dependent on creation order, you are always going to be in trouble relying on the streaming mechanism. Just one addition or removal of a(n other) component on the form/datamodule can throw your order out of whack.
To ensure proper creation order, you'd be better off creating them at run time. Just note that when you create components at run-time the Loaded method will not be called. You will either have to do it yourself or move the code to some init method that you call after you create your components.
You can right click a form/datamodule and select the "Creation order" item. It will allow you to select the creation order of "non visual" components. Visual ones should follow the tab order, but I am not really sure about that.
Update: I was wrong about the tab order, but it looks the visual controls are streamed to the .dfm in Z-order. If the controls are instantiated following the order they are in the .dfm, you can use Edit -> Bring to front/send to back (or the Control menu in the form context menu) to change the z order. As long as the controls do not overlap you should be enough free to change it.