Examples Delphi

{
Q: Is there a way to associate a string with each component?
A: Since the Tag property is a longint, you can type cast it
as a Pointer or PChar. So, you can basically store a pointer
to a record by using the Tag property.
Note: You're not going to be able to store the string, or
pointer rather, at design time. This is something you'll have
to do at run time. Take a look at this example:
}
var
i: integer;
begin
for i := 0 to ComponentCount - 1 do
if Components[i] is TEdit then
Components[i].Tag := LongInt(NewStr('Hello '+IntToStr(i)));
end;
Here, I loop through the components on the form. If the
component is a TEdit, I assign a pointer to a string to its Tag
property. The NewStr function returns a PString (pointer to a
string). A pointer is basically the same as a longint or
better, occupies the same number of bytes in memory. Therefore,
you can type cast the return value of NewStr as a LongInt and
store it in the Tag property of the TEdit component. Keep in
mind that this could have been a pointer to an entire record.
Now I'll use that value:
var
i: integer;
begin
for i := 0 to ComponentCount - 1 do
if Components[i] is TEdit then begin
TEdit(Components[i]).Text := PString(Components[i].Tag)^;
DisposeStr(PString(Components[i].Tag));
end;
end;
Here, again I loop through the components and work on only the
TEdits. This time, I extract the value of the component's Tag
property by typecasting it as a PString (Pointer to a string)
and assigning that value to the TEdit's Text property. Of
course, I must dereference it with the caret (^) symbol. Once
I do that, I dispose of the string stored in the edit
component. Important note: if you store anything in the
TEdit's Tag property as a pointer, you are responsible for
disposing of it also.
FYI, Since Delphi objects are really pointers to class
instances, you can also store objects in the Tag property. As
long as you remember to Free them.
Three methods spring to mind to use Tags to access strings that
persist from app to app.
1. If your strings stay the same forever, create a string
resource in Resource Workshop (or equiv) and use the Tags as
indexes into your string resource.
2. Use TIniFile and create a section for your strings, and
give each string a name with number so that your ini file has a
section like this:
[strings]
string1=Aristotle
string2=Plato
string3=Well this is Delphi, after all
Then you can fetch them back out this way:
var s1: string;
...
s1 := IniFile1.ReadString('strings', 'string'+IntToStr(Tag), '');
3. Put your strings into a file, with each followed by a
carriage return. Read them into a TStringList. Then your Tags
become an index into this stringlist:
StringList1.LoadFromFile('slist.txt');
...
s1 := StringList1[Tag];
Given the way Delphi is set up, I think the inifile method is easiest.