* Small observer demo from Graeme Geldenhuys (bug ID 23329)

git-svn-id: trunk@23092 -

.gitattributes

@@ -1782,6 +1782,7 @@ packages/fcl-base/examples/crittest.pp svneol=native#text/plain
 packages/fcl-base/examples/dbugsrv.pp svneol=native#text/plain
 packages/fcl-base/examples/debugtest.pp svneol=native#text/plain
 packages/fcl-base/examples/decodeascii85.pp svneol=native#text/plain
+packages/fcl-base/examples/dobserver.pp svneol=native#text/plain
 packages/fcl-base/examples/doecho.pp svneol=native#text/plain
 packages/fcl-base/examples/dparser.pp svneol=native#text/plain
 packages/fcl-base/examples/dsockcli.pp svneol=native#text/plain

packages/fcl-base/examples/dobserver.pp

@@ -0,0 +1,67 @@
+{ This demo is very basic, but shows the Observer support in the RTL }
+program dobserver;
+
+{$mode objfpc}{$h+}
+{$ifdef mswindows}{$apptype console}{$endif}
+
+uses
+ Classes, SysUtils, typinfo;
+
+type
+  TMyObserver = class(TObject, IFPObserver)
+  private
+    procedure FPOObservedChanged(ASender : TObject; Operation : TFPObservedOperation; Data : Pointer);
+  end; 
+  
+{ TMyObserver }
+
+procedure TMyObserver.FPOObservedChanged(ASender: TObject;
+               Operation: TFPObservedOperation; Data: Pointer);
+
+  function OperationToString(AOperation: TFPObservedOperation): string;
+  begin
+    result := GetEnumName(TypeInfo(TFPObservedOperation),
+                         Ord(AOperation));
+  end;
+var
+  intf: IFPObserved;
+begin
+  if Operation = ooFree then
+  begin
+    writeln('[ooFree] detected so we should detach ourselves');
+    if Supports(ASender, IFPObserved, intf) then
+      intf.FPODetachObserver(self);
+  end
+  else
+  begin
+    writeln(ASender.ClassName + ' has changed ['+
+      OperationToString(Operation) + ']');
+  end;
+end;
+  
+var
+  sl: TStringList;
+  observer: TMyObserver;
+  intf: IFPObserved;
+begin
+  { This stringlist will be the subject (observed) }
+  sl := TStringList.Create;
+  { this instance will be the observer - notified when StringList changes }
+  observer := TMyObserver.Create;
+
+  { attach observer }  
+  if Supports(sl, IFPObserved, intf) then
+  begin
+    intf.FPOAttachObserver(observer);
+  end;
+  
+  { Do something to the stringlist }
+  sl.Add('Item one');
+  sl.Add('Item two');
+  sl.Delete(0);
+  
+  { Clean-up code - also shows ooFree operation }
+  sl.Free;
+  observer.Free;
+end.
+