Author: Jonas Bilinkevicius

I'm using a component which is able to save the caption of components to a textfile 
and then retrieve it again. This works quite nice since if one wants another 
language one can just change some captions and load the desired language. The only 
problem is that it is using only the well known Windows controls and is also 
checking if a component is of a certain type. Of course I want to be able to use it 
for all components, so how would I be able to check all the components on a form 
for caption properties (even if it is e.g. in a item of a component) without having 
to do type checking etc.?

Answer:

You can use functions from the TypInfo unit. You'll need a GetPropInfo to get 
information about the property, GetStrProp and SetStrProp functions to read and set 
a new caption for components. The example below is a component which can save the 
captions of all components on a form to the text file and load them back after the 
form was loaded. There is also a design time component editor which you need to 
save and load captions (see a popup menu over the component).

1   {The main component}
2   TMyCaptionReader = class(TComponent)
3   protected
4     FFileName: string;
5     procedure Loaded; override;
6   public
7     constructor Create(AOwner: TComponent); override;
8     procedure ReadCaptions;
9     procedure WriteCaptions;
10  published
11    property FileName: string read FFileName write FFileName;
12  end;
13  
14  {The component editor}
15  TMyCaptionReaderEditor = class(TDefaultEditor)
16  public
17    procedure ExecuteVerb(Index: Integer); override;
18    function GetVerb(Index: Integer): string; override;
19    function GetVerbCount: Integer; override;
20  end;
21  
22  { ... }
23  
24  procedure TMyCaptionReaderEditor.ExecuteVerb(Index: Integer);
25  begin
26    case Index of
27      0: TMyCaptionReader(Component).WriteCaptions;
28      1: TMyCaptionReader(Component).ReadCaptions;
29    else
30      inherited ExecuteVerb(Index)
31    end;
32  end;
33  
34  function TMyCaptionReaderEditor.GetVerb(Index: Integer): string;
35  begin
36    case Index of
37      0: Result := 'Write Captions...';
38      1: Result := 'Read Captions...'
39    else
40      Result := inherited GetVerb(Index);
41    end;
42  end;
43  
44  function TMyCaptionReaderEditor.GetVerbCount: Integer;
45  begin
46    Result := 2;
47  end;
48  
49  constructor TMyCaptionReader.Create(AOwner: TComponent);
50  begin
51    inherited Create(AOwner);
52    FFileName := 'TheFile.txt';
53  end;
54  
55  procedure TMyCaptionReader.Loaded;
56  begin
57    inherited Loaded;
58    ReadCaptions;
59  end;
60  
61  procedure TMyCaptionReader.ReadCaptions;
62  var
63    XStrings: TStringList;
64    XComponent: TComponent;
65    XPropInfo: PPropInfo;
66    XName, XCaption: string;
67    i, XPos: integer;
68  begin
69    if not FileExists(FFileName) then
70      exit;
71    XStrings := TStringList.Create;
72    try
73      XStrings.LoadFromFile(FFileName);
74      for i := 0 to XStrings.Count - 1 do
75      begin
76        XPos := pos('=', XStrings[i]);
77        if XPos > -1 then
78        begin
79          XName := copy(XStrings[i], 0, XPos - 1);
80          XCaption := copy(XStrings[i], XPos + 1, length(XStrings[i]) - 1);
81          XComponent := Owner.FindComponent(XName);
82          if Assigned(XComponent) then
83          begin
84            XPropInfo := GetPropInfo(XComponent, 'Caption');
85            if Assigned(XPropInfo) then
86              SetStrProp(XComponent, 'Caption', XCaption);
87          end;
88        end;
89      end;
90    finally
91      XStrings.Free;
92    end;
93  end;
94  
95  procedure TMyCaptionReader.WriteCaptions;
96  var
97    XStrings: TStringList;
98    XComponent: TComponent;
99    XPropInfo: PPropInfo;
100   XCaption: string;
101   i: integer;
102 begin
103   XStrings := TStringList.Create;
104   try
105     if Assigned(Owner) then
106     begin
107       for i := 0 to Owner.ComponentCount - 1 do
108       begin
109         XComponent := Owner.Components[i];
110         if Assigned(XComponent) then
111         begin
112           try
113             XPropInfo := GetPropInfo(XComponent, 'Caption');
114             if Assigned(XPropInfo) then
115             begin
116               XCaption := GetStrProp(XComponent, 'Caption');
117               XStrings.Add(XComponent.Name + '=' + XCaption);
118             end;
119           except
120           end;
121         end;
122       end;
123     end;
124     XStrings.SaveToFile(FFileName);
125   finally
126     XStrings.Free;
127   end;
128 end;
129 
130 //Here's how the Register procedure could be:
131 
132 procedure register;
133 begin
134   RegisterComponents('My Components', [TMyCaptionReader]);
135   RegisterComponentEditor(TMyCaptionReader, TMyCaptionReaderEditor);
136 end;