Author: Jonas Bilinkevicius

How to determine if an object has a particular property

Answer:

The first hasprop will return True if a property of name prop exists, eg. 
hasprop(MyLabel,'Caption') will return true while hasprop(MyEdit,'Caption') will 
return false. The second one will set property prop to string value s if it exists 
and is a string type property.

1   hasprop(comp: TComponent; const prop: string): Boolean;
2   var
3     proplist: PPropList;
4     numprops, i: Integer;
5   begin
6     result := false;
7     getmem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
8     try
9       NumProps := getproplist(comp.classInfo, tkProperties, proplist);
10      for i := 0 to pred(NumProps) do
11      begin
12        if comparetext(proplist[i]^.Name, prop) = 0 then
13        begin
14          result := true;
15          break;
16        end;
17      end;
18    finally
19      freemem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
20    end;
21  end;
22  
23  procedure setcomppropstring(comp: TComponent; const prop, s: string);
24  var
25    proplist: PPropList;
26    numprops, i: Integer;
27  begin
28    getmem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
29    try
30      NumProps := getproplist(comp.classInfo, tkProperties, proplist);
31      for i := 0 to pred(NumProps) do
32      begin
33        if (comparetext(proplist[i]^.Name, prop) = 0) and
34          (comparetext(proplist[i]^.proptype^.name, 'string') = 0 then
35          begin
36            setStrProp(comp, proplist[i], s);
37            break;
38          end;
39      end;
40    finally
41      freemem(proplist, getTypeData(comp.classinfo)^.propcount * Sizeof(Pointer));
42    end;
43  end;