View source for ClassGroup pseudo-property of TDataModule

{{Parent|Creating and Editing Standard Data Modules}}
__TOC__

== Effects of the ClassGroup pseudo-property ==
[[lib_en:System.Classes.TDataModule|System.Classes.TDataModule]] and its descendant classes, such as [[lib_en:Web.HTTPApp.TWebModule|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 [[Setting the Framework Affinity for a Data Module|set a framework-specific value for '''ClassGroup''']] in the '''[[Object Inspector]]''' in order to enable framework-specific nonvisual components such as the following:
** '''[[lib_en:Vcl.ActnList.TActionList|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.)

Because the '''ClassGroup''' pseudo-property is used only by the IDE and is not a compiler-generated property (hence, 'pseudo-property'), '''ClassGroup''' is not documented in the compiler-generated [[lib_en:Main Page|Libraries Reference]]. The page you are reading is the documentation for '''ClassGroup'''.

{{Note| The two frameworks, '''VCL''' and '''FMX''', are not mutually compatible.  For this reason, combining VCL and FMX in an application is not supported.  See [[FireMonkey#VCL_Is_Incompatible_with_FireMonkey|FireMonkey Application Platform]].}}

== ClassGroup Values ==
Following are the '''ClassGroup''' values you can choose in the '''Object Inspector''', including the framework and the RTL elements that can be used with each framework-specific choice:

{| border="1" frame="hsides" rules="rows"
! '''ClassGroup'''
! '''Associated Framework '''
! '''Run-Time Library '''
|- valign="top"
|
{{Code|System.Classes.TPersistent}}
|
None (Framework-neutral)
|
{{Delphi}} RTL

(excluding unsupported framework-specific elements)
|- valign="top"
|
{{Code|Vcl.Controls.TControl}}
|
VCL framework
|
{{Delphi}} RTL

(excluding unsupported framework-specific elements)
|- valign="top"
|
{{Code|FMX.Controls.TControl}}
|
FMX framework
|
{{Delphi}} RTL 

(excluding unsupported framework-specific elements)
|}

== TDataModule is Initially Framework-Neutral; You Set Framework Affinity with ClassGroup ==

When you create a data module, the unit file initially contains a directive that sets the '''ClassGroup''' pseudo-property to a framework-neutral base value ('''System.Classes.TPersistent'''), as follows:

'''{{Delphi}}:'''
<source lang='delphi'> {%CLASSGROUP 'System.Classes.TPersistent'} </source>

'''C++:'''
<source lang='cpp'> #pragma classgroup "System.Classes.TPersistent" </source>

{{Note| This directive is used only by the IDE and indicates the data module's relationship with a particular component framework, if any. Then the IDE enforces the kinds of components that you can drop on the data module.  <br>
When you change the '''ClassGroup''' value, the directive is automatically changed in your code.
}}

Because '''[[lib_en:System.Classes.TDataModule|TDataModule]]''' is initally framework-neutral, you can use a data module with either the VCL or the {{FM}} framework. 
This also means that framework-specific classes and members (such as '''[[lib_en:Vcl.ActnList.TActionList|Vcl.ActnList.TActionList]]''' and '''[[lib_en:FMX.Types.TTimer|FMX.Types.TTimer]]''') are not available in the '''Tool Palette''' for a framework-neutral data module.  You can include the appropriate framework-specific classes and members by going to the '''Object Inspector''' and setting the '''ClassGroup''' property of your data module to indicate your correct framework, as one of the following:
* Vcl.Controls.TControl 
* FMX.Controls.TControl (OS X)

=== Examples of Framework-Specific Nonvisual Components ===
*'''[[lib_en:Vcl.ActnList.TActionList|TActionList]]''' is a VCL nonvisual component and as such it does not appear in the '''Tool Palette''' for a data module whose '''ClassGroup''' pseudo-property is '''System.Classes.TPersistent''' (framework-neutral) rather than '''Vcl.Controls.TControl''' (framework-specific). Likewise, TActionList is not available if the '''ClassGroup''' is set to '''FMX.Controls.TControl'''.

*'''TTimer''' has two framework-specific implementations, as follows: 
** [[lib_en:FMX.Types.TTimer|FMX.Types.TTimer]]
** [[lib_en:Vcl.ExtCtrls.TTimer|Vcl.ExtCtrls.TTimer]]
*:In both cases, '''TTimer''' is only available in the '''Tool Palette''' when the '''ClassGroup''' property is set to a framework-specific value, rather than the framework-neutral '''System.Classes.TPersistent'''. But because '''TTimer''' has both a VCL and an FMX implementation, make sure that you select the correct '''ClassGroup''' value for your data module, to match the application framework, or errors can occur.

* Examples of other framework-specific components that are affected by the '''ClassGroup''' value:
**''' TMainMenu:''' [[lib_en:Vcl.Menus.TMainMenu|Vcl.Menus.TMainMenu]] and [[lib_en:FMX.Menus.TMainMenu|FMX.Menus.TMainMenu]]
** '''TPopupMenu:''' [[lib_en:Vcl.Menus.TPopupMenu|Vcl.Menus.TPopupMenu]] and [[lib_en:FMX.Menus.TPopupMenu|FMX.Menus.TPopupMenu]]
** '''TOpenDialog:''' [[lib_en:Vcl.Dialogs.TOpenDialog|Vcl.Dialogs.TOpenDialog]] and [[lib_en:FMX.Dialogs.TOpenDialog|FMX.Dialogs.TOpenDialog]]

After you select the Classgroup you want, you might need to switch to the Edit tab and back to the Design tab in order to refresh the '''Tool Palette''' to reflect your Classgroup choice.

== Troubleshooting Error Situations ==
If you create a data module inside a Windows VCL Application, and set an FMX value for the '''ClassGroup''' property, the following message is displayed when you try to drop an FMX component on the data module:
 
: Class &lt;classname&gt; does not apply to this module.

This message occurs when the '''ClassGroup''' value of the data module does not match the framework of the application.

A similar message appears if you create a {{FM}} application, add a data module, select the '''ClassGroup''' value ''Vcl.Controls.TControl'', and try to drop a TTimer on the data module, because the [[lib_en:Vcl.ExtCtrls.TTimer|Vcl.ExtCtrls.TTimer]] nonvisual component is not compatible with the {{FM}} framework.

The following message might also be displayed by the IDE:

: The following component(s) are not available in the specified class group. 
: This is likely to cause compile or runtime errors.
:
: FMX.Types.TTimer

If you try to compile a project that has a '''ClassGroup''' value that is not compatible with the application framework, you might see compile errors for elements that are not supported in the current framework. Possible errors you might encounter include the following:
* [[X1026 File not found '%s' (Delphi)]]
* [[E2109 Not an allowed type (C++)]]
* [[E2209 Unable to open include file 'filename' (C++)]]
* [[Unresolved external 'symbol' referenced from 'module'|Unresolved external 'symbol' referenced from 'module' (C++ Linker)]]

== See Also ==
* [[lib_en:System.Classes.TDataModule_Properties|Properties of System.Classes.TDataModule]]
* [[Using Data Modules]]
* [[Setting the Framework Affinity for a Data Module]]

[[Category:Windows Developer's Guide]]
[[Category:{{Delphi}}]][[Category:C++]]

[[de:Pseudo-Eigenschaft ClassGroup von TDataModule]]
[[fr:Pseudo-propriété ClassGroup de TDataModule]]
[[ja:TDataModule の ClassGroup 疑似プロパティ]]