Delphi XE2 Data Module expects only database components?

Asked 31/12, 2012 at 3:55 Answered 31/12, 2012 at 10:16

In prior versions of Delphi, I have used the data module (TDataModule) as a place to keep non-visual components to avoid cluttering up the main form. In Delphi XE2, when I create a new data module, it only allows me to place database related components in it (such as TADOConnection and TDataSource). Why is this and how can I put other components in it? Is there an alternative?

Garland answered 31/12, 2012 at 3:55 Comment(8)

Can you give an example of a non-visual component (one that is provided with Delphi, preferably) that it won't allow? I've never seen this problem. – Wordy 31/12, 2012 at 4:1

Like a TImageList or TMainMenu or TActionManager - When I try to paste one, it says the component class is not found, and the palette only shows database related components. – Garland 31/12, 2012 at 4:2

Could it be my specific edition of RAD Studio? But then I have Enterprise, should have about everything. – Garland 31/12, 2012 at 4:3

I can confirm this with File->New->VCL Forms Application, and then File->New->Other->Delphi Files->Datamodule, which leaves only the database, Intraweb, FastReports, and Indy components available in the component palette. (TImageList and TActionList are not there.) Using the Pro SKU, so it's not that causing the problem. – Wordy 31/12, 2012 at 4:15

Interesting, strange why this limitation would exist in the first place. The company's not ready to upgrade to XE3 quite yet, we're still settling into XE2. – Garland 31/12, 2012 at 5:0

@JerryDodge can you switch to datamodule -> F6 -> type component name -> RETURN? this is weird, never had this... – Applesauce 31/12, 2012 at 5:5

@Ken In fact it wasn't broken in XE2. And XE3 didn't fix anything. What XE3 did was move actions out of the VCL and into a lower level and so be available to all frameworks. – Interknit 31/12, 2012 at 10:19

@David: Thanks. I was obviously wrong. :-) – Wordy 31/12, 2012 at 22:15

Data modules changed with the XE2 release. Remember that XE2 introduced a new component framework, FireMonkey, in addition to the long-standing VCL. A new pseudo-property, named ClassGroup was added to data modules. This controls what components can be added to the data module in the IDE designer.

The default ClassGroup for a data module is System.Classes.TPersistent. This specifies that the data module is framework neutral and so accepts neither VCL components nor FMX components.

In your case you probably want to accept VCL components so you need to specify a ClassGroup of Vcl.Controls.TControl.

Read all about ClassGroup in the documentation.

System.Classes.TDataModule and its descendant classes, such as Web.HTTPApp.TWebModule, have a pseudo-property named ClassGroup that does the following:

Determines the framework affinity for the data module. That is, ClassGroup specifies that the data module is either framework-neutral or is to work with a specific framework (namely, VCL or FMX).

Enables framework-specific nonvisual components in the Tool Palette. You need to set a framework-specific value for ClassGroup in the Object Inspector in order to enable framework-specific nonvisual components such as the following:

TActionList is VCL-only, and so to enable TActionList in the Tool Palette, you must set ClassGroup to the VCL setting.

TTimer exists in both FMX and VCL. To enable TTimer for the correct framework, you must set ClassGroup to either FMX or VCL, to match the framework of the parent application. (TTimer and TActionList are further discussed later in this topic.)

Interknit answered 31/12, 2012 at 10:16 Comment(0)

This (buggy) behavior in

unit Unit2;

interface

uses
  System.SysUtils, System.Classes;

type
  TDataModule2 = class(TDataModule)
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  DataModule2: TDataModule2;

implementation

{%CLASSGROUP 'System.Classes.TPersistent'}

{$R *.dfm}

end.

is caused by the line

{%CLASSGROUP 'System.Classes.TPersistent'}

To get rid of just delete or modify the line into

{.%CLASSGROUP 'System.Classes.TPersistent'}

After switch to Design View you will see all the components as you expect.

(Delphi XE2 16.0.4504.48759)

Inhumation answered 31/12, 2012 at 7:52 Comment(8)

Perfecto! I knew it had to be something simple, as always. – Garland 31/12, 2012 at 8:17

PS - The hard part was figuring out how to create the data module in a way that it could be used throughout the app with common components - I wound up creating/destroying it in a try..finally block in the project's main dpr file, wrapping the form creation and Run. – Garland 31/12, 2012 at 8:37

See also #11250519 – Bucksaw 31/12, 2012 at 9:32

We have no problems in an app that was migrated from D2007 to XE2 (TImageList, TcxSchedulerStorage etc), but its good to know this when we add another data module. – Bucksaw 31/12, 2012 at 9:36

You can do this right inside the Object Inspector: select the datamodule and set its ClassGroup property accordingly. Then close and reopen the damodule unit. – Landowska 31/12, 2012 at 9:38

There's nothing buggy here. And the right solution for Jerry is to set the ClassGroup to VCL. – Interknit 31/12, 2012 at 10:25

Now that it's solved, I'm pondering why would TPersistent make the data module only allow database related components? How does that work? A TComponent is a TPersistent. – Garland 31/12, 2012 at 10:41

It doesn't just allow database controls. It blocks VCL and FMX components. In XE3 actions are allowed because they are no longer VCL specific. And as for TPersistent. It's just a name. Thr docs make it clear what it means. – Interknit 31/12, 2012 at 11:0

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