The TypeInfo unit of Delphi declares several types and functions that gives you
easy access to the puplished properties of an object and other informations.
You can obtain a list of the published properties of a class and get the name an
type of each property.
The TypeInfo funtion returns a pointer to a type information record. The TypInfo
unit declares a real type, that is, a pointer to a TTypeInfo record :
1
2 PTypeInfo = ^TTypeInfo;
3 TTypeInfo = record
4 Kind: TTypeKind;
5 Name: ShortString;
6 end;
7
The TTypeKind datatype describes the Datatype , returned by the GetTypeData
function.
8
9 TTypeKind = (tkUnknown, tkInteger, tkChar, tkEnumeration, tkFloat,
10 tkString, tkSet, tkClass, tkMethod, tkWChar, tkLString, tkWString,
11 tkVariant, tkArray, tkRecord, tkInterface, tkInt64, tkDynArray);
12 TTypeKinds = set of TTypeKind;
13
14
Well ... for our first step to access the objects published properties we need to
use the PPropInfo-pointer.
15
16 PPropInfo = ^TPropInfo;
17 TPropInfo = packed record
18 PropType: PPTypeInfo;
19 GetProc: Pointer;
20 SetProc: Pointer;
21 StoredProc: Pointer;
22 Index: Integer;
23 default: Longint;
24 NameIndex: SmallInt;
25 Name: ShortString;
26 end;
To clarify it, please take a look at this example :
27
28 function GetFontSize(Obj:TPersistent):Integer;
29 {
30 in this Procedure we want to get the pPropInfo-pointer - pointing
31 on the Font-Property from an arbitrary TPersistent-Class.
32 The return-value in this instance will be the font-size ( if the font
33 property exists , if not -> the return value will be -1 )
34 }
35 var PropInfo:PPropInfo;
36 begin
37 RESULT:=-1;
38 // Get the PPropInfo-Pointer for Font of the TPersistent obj
39 PropInfo:=GetPropInfo(Obj,'Font');
40 // At first we will find out if the property FONT exists
41 if PropInfo=nil then
42 EXIT; // The Property doesn't exists
43 {
44 TFont is not an ordinal-Type - therefore will have to control if
45 Typekind of the TypeInfo-Class is set to tkClass
46 }
47 if PropInfo.PropType^.Kind <>tkClass then
48 EXIT; // property isn't a tkClass type
49 {
50 now, we now that the TypeKind of die PropInfo-pointer is a class .
51 last but not least we will use the GetObjectProp, the return-value
52 of this function is a TObject. Subsequently, we will use this object as
53 a TFont to get the Size value.
54 }
55 RESULT:=( (GetObjectProp(Obj,PropInfo)) as TFont).Size;
56 end;
But to get the complete list of all properties of a TPersistent-Class we will need
the pPropList-Type . This type is a simple pointer-array and the magic key to all
Property-Informations and their structures.
Take a look at this :
57
58 procedure TForm1.Button1Click(Sender: TObject);
59
60 const tkOrdinal = [tkEnumeration,tkInteger,tkChar,tkSet,tkWChar]; //Filter
61
62 begin
63 {
64 in this method of the mainform-class we are seeking for all ordinal-type
65 properties of the edit1-component. The from the GetPropertyList method
66 returned list of all properties will be written into the Listbox1. You can
67 replace the obj parameter with an arbitrary TObject ( but usually TPersistent
68 objects ).
69 For another filter please take a look at the TTypeKinds-set.
70 }
71 GetPropertyList(Edit1,ListBox1.Items,tkOrdinal);
72 end;
73
74 procedure GetPropertyList(Obj:TObject ;List: TStrings;Filter: TTypeKinds);
75 var PropList:pPropList;
76 count,i : Integer;
77 begin
78 List.Clear;
79 // Here we'll get the count of the given properties, ...
80 Count := GetPropList(Obj.ClassInfo, Filter, nil);
81 // ...and create room for the PropList,...
82 GetMem(PropList,Count * SizeOf(PPropInfo));
83 // ...get the Proplist-Data,...
84 GetPropList(Obj.ClassInfo, Filter, PropList);
85 // ...and write the property-names into the StringList
86 for i:=0 to Count -1 do
87 List.Add(Proplist[i].Name);
88 end;
That's it ---- actually easy , or?
best regards
Boris Benjamin Wittfoth
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