Enumerating Published Properties and Sub-Properties in Delphi

Question

Sorry if the question was asked before. I have some definition of some components as follows (please guide me if this is wrong, because I'm a newbie). What I'm trying to do is list all published properties of derived components, especially sub-properties. I can list property names, however, is it possible to list published properties for which I can access elements (as in sub-properties) at runtime? something like returning properties one by one, like getfirst / getnext, to the end?

type TStringArray = array of string; TGenericColumnDef = class(TPersistent) private fColumnName : String; fColumnNumber : Integer; fColumnDisplay : string; fColumnDescription : string; fColumnDataType : integer; fColumnEditorType : integer; // fMyEvent: TNotifyEvent; protected public constructor create(AOwner: TComponent); virtual; published property ColumnName : String read fColumnName write fColumnName; property ColumnNumber : integer read fColumnNumber write fColumnNumber; //property MyEvent: TNotifyEvent read fMyEvent write fMyEvent; end; TGenericAsset = class(Tcomponent) //TPersistent private { Private declarations } fCiteID : TGenericColumnDef; fCiteType : TGenericColumnDef; fTitle : TGenericColumnDef; fAuthor : TGenericColumnDef; fPropertyCount : integer; function GetPropertyCount : integer; function GetNextPropertyIndex: integer; property CountProperties : integer read GetPropertyCount;// write fPropertyCount protected { Protected declarations } FOwner: TObject; public { Public declarations } constructor Create(AOwner: TComponent); override; destructor destory ; virtual; function GetColumnNameByColumnNumber(ColumnNumber : Integer) : String; function GetColumnNames : TStringArray; // function GetFirst : TGenericColumnDef; published property CiteID : TGenericColumnDef read fCiteID write fCiteID; property CiteType : TGenericColumnDef read fCiteType write fCiteType; property Title : TGenericColumnDef read fTitle write fTitle; property Author : TGenericColumnDef read fAuthor write fAuthor; //property Nthproperty ......... end; //derived from TGenericAsset type TEditedBook = class(TGenericAsset) private protected public published property CiteID : TGenericColumnDef read fCiteID write fCiteID; property Title : TGenericColumnDef read fTitle write fTitle; property Author : TGenericColumnDef read fAuthor write fAuthor; end; 

Any points or recommendations (sample code) are highly appreciated. Thanks in advance.

Answer 1

While he does not specifically answer your question, the code below (donated by old Peter Borland Delphi newsgroups several years ago by Dr. Peter Below "TeamB") shows how to use RTTI to clone another component. It shows how to get (and set) sub-properties, such as other objects, enumerated types, etc. That should be enough to get you started. I left Peter's comments in the code, as well as a sample of using it as some example code below the function. (I also kept its code formatting and the weird letter shell of some keywords. :)

 // Unfortunately there is no easy way to "clone" a component in a way that // will also preserve event handlers. It can be done using run-time type // information and routines form the TypInfo unit, though. Try the following // routine. It is only superficially tested. Uses TypInfo; {-- CloneComponent ----------------------------------------------------} {: Make a copy of a component. @Param anObj is the component to copy @Param cloneChildren if true and anObj is a TWincontrol then all its child controls will also be copied. @Param aParent is the parent to use if anObj is a TControl. @Returns the new object reference. It will have the same owner as anObj and passes into the responsibility of the caller. @Precondition anObj <> nil @Desc The method creates a new object of the same class as anObj and then uses TypInfo routines to copy all published properties. The logic used for object properties is similar to what the form loading code uses: if a property refers to a TComponent the component reference is copied. If it refers to a TPersistent descendent the Assign method is used to copy the objects contents. Currently TCollections do not receive any special treatment, which may be necessary. <BR> Note: the routine will not copy any objects *owned* by anObj, so it cannot be used as is to clone a top-level container like a form, frame, or datamodule. Those can be copied using WriteComponent and ReadComponent with a TMemoryStream. }{ Created 12.4.2002 by P. Below -----------------------------------------------------------------------} Function CloneComponent( anObj: TComponent; cloneChildren: Boolean = false; aParent: TWinControl = nil ): TComponent; Var numProps, I : Integer; props: PPropList; PropInfo: PPropInfo; obj, obj2: TObject; Begin { CloneComponent } Assert( Assigned( anObj )); Result := TComponentClass( anObj.ClassType ).Create( anObj.Owner ); Try numProps := GetPropList(anObj, props ); Try For I := 0 To numProps - 1 Do Begin PropInfo := props^[I]; Case PropInfo^.PropType^.Kind Of tkInteger, tkChar, tkEnumeration, tkSet, tkWChar: SetOrdProp( Result, propinfo, GetOrdProp( anObj, propinfo )); tkFloat: SetFloatProp( Result, propinfo, GetFloatProp( anObj, propinfo )); tkString, tkLString: If not SameText( propinfo^.name, 'Name' ) Then SetStrProp( Result, propinfo, GetStrProp( anObj, propinfo )); tkWString: SetWideStrProp( Result, propinfo, GetWideStrProp( anObj, propinfo )); tkMethod: SetMethodProp( Result, propinfo, GetMethodProp( anObj, propinfo )); tkInt64: SetInt64Prop( Result, propinfo, GetInt64Prop( anObj, propinfo )); tkVariant: SetVariantProp( Result, propinfo, GetVariantProp( anObj, propinfo )); tkInterface: SetInterfaceProp( Result, propinfo, GetInterfaceProp( anObj, propinfo )); tkClass: Begin obj := GetObjectProp( anObj, propinfo ); If Assigned( obj ) Then Begin If obj Is TComponent Then SetObjectProp( Result, propinfo, obj ) Else If obj Is TPersistent Then Begin obj2 := GetObjectProp( result, propinfo, TPersistent); If Assigned( obj2 ) Then TPersistent( obj2 ).Assign( TPersistent(obj)); End; { If } End; { If } End; { Case tkClass } Else // we don't handle these property types: // tkArray, tkRecord, tkDynArray End; { Case } End; { For } Finally FreeMem( props ); End; { Finally } If anObj Is TControl Then TControl( result ).Parent := aParent; If cloneChildren and (anObj Is TWinControl ) Then For i:= 0 To TWinControl( anObj ).ControlCount-1 Do CloneComponent( TWinControl( anObj ).Controls[i], true, TWinControl( Result ) ); Except Result.Free; raise End; { Except } End; { CloneComponent } procedure TForm1.GroupBox1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer); begin memo1.lines.add('Click on groupbox '+(sender as TComponent).Name ); end; procedure TForm1.Button1Click(Sender: TObject); Var ctrl: TWinControl; begin ctrl := CloneComponent( groupbox1, true, self ) as TWincontrol; With ctrl Do SetBounds( left, top+height+8, width, height ); memo1.Lines.add( Format('Controlcount: %d', [ctrl.controlcount])); end;