Saving a value even after program is closed and reopened

Question

I would like to know how to save the contents of a "variable" after program is closed and reopened.

for eg: iCount:=0; inc(iCount)=1;

when i close the program and reopen i want iCount to contain 1. Thank you.

Answer 1

There are many ways to do this. You need to save the value somewhere: in a file, in the Windows registry, in the cloud, ...

File

Perhaps the easiest approach is to use an INI file. Try this:

1. Create a new VCL application.

2. Add a field FMyNumber: Integer to the main form.

3. To the main form, add the following methods (and make sure to include IniFiles and IOUtils in the implementation section's uses list):

   function TForm1.GetSettingsFileName: TFileName;
   begin
     Result := TPath.GetHomePath + '\Fuzail\TestApp';
     ForceDirectories(Result);
     Result := Result + '\settings.ini';
   end;
   
   procedure TForm1.LoadSettings;
   var
     Ini: TMemIniFile;
   begin
     Ini := TMemIniFile.Create(GetSettingsFileName);
     try
       FMyNumber := Ini.ReadInteger('Settings', 'MyNumber', 0);
     finally
       Ini.Free;
     end;
   end;
   
   procedure TForm1.SaveSettings;
   var
     Ini: TMemIniFile;
   begin
     Ini := TMemIniFile.Create(GetSettingsFileName);
     try
       Ini.WriteInteger('Settings', 'MyNumber', FMyNumber);
       Ini.UpdateFile;
     finally
       Ini.Free;
     end;
   end;
   

4. Now make sure to call these when your application is starting and shutting down:

   procedure TForm1.FormCreate(Sender: TObject);
   begin
     LoadSettings;
   end;
   
   procedure TForm1.FormDestroy(Sender: TObject);
   begin
     SaveSettings;
   end;
   

   Now the value of FMyNumber is saved between the sessions!

Registry

Another common approach, probably, is to use the registry. Try this:

1. Create a new VCL application.

2. Add a field FMyNumber: Integer to the main form.

3. To the main form, add the following methods (and make sure to include Registry in the implementation section's uses list):

   procedure TForm1.LoadSettings;
   var
     Reg: TRegistry;
   begin
     Reg := TRegistry.Create;
     try
       Reg.RootKey := HKEY_CURRENT_USER;
       if Reg.OpenKey('\Software\Fuzail\TestApp', False) then
         try
           if Reg.ValueExists('MyNumber') then
             FMyNumber := Reg.ReadInteger('MyNumber')
         finally
           Reg.CloseKey;
         end;
     finally
       Reg.Free;
     end;
   end;
   
   procedure TForm1.SaveSettings;
   var
     Reg: TRegistry;
   begin
     Reg := TRegistry.Create;
     try
       Reg.RootKey := HKEY_CURRENT_USER;
       if Reg.OpenKey('\Software\Fuzail\TestApp', True) then
         try
           Reg.WriteInteger('MyNumber', FMyNumber);
         finally
           Reg.CloseKey;
         end;
     finally
       Reg.Free;
     end;
   end;
   

4. Now make sure to call these when your application is starting and shutting down:

   procedure TForm1.FormCreate(Sender: TObject);
   begin
     LoadSettings;
   end;
   
   procedure TForm1.FormDestroy(Sender: TObject);
   begin
     SaveSettings;
   end;
   

   Again the value of FMyNumber is saved between the sessions!