Storing the value of variable using TRadioGroup

Question

I want to change the value of T according to a particular selection but it's not changing. Please have a look. The variable T has been declared along with Form1:TForm1 before 'implementation'. Basically, T should get assigned a linear or non linear equation depending upon the the selection of the respected radio buttons. I put a TEdit in the form so as to get an idea whether it is working or not. The last part is just a way to check by taking an example of Integer values.

Also, if I am not able to give a clear idea then just suggest me how to store a value of the concerned value using the Radiobuttons of the RadioGroup.

procedure TForm1.RadioGroup1Click(Sender: TObject);
begin

 if RadioGroup1.Items[RadioGroup1.ItemIndex] = 'Linear Tension' then
    T:= 5;
  if RadioGroup1.Items[RadioGroup1.ItemIndex] = 'Non-Linear tension' then
    T:= 10;
end;

procedure TForm1.Edit1Change(Sender: TObject);

var
code: Integer;
value: Real;
begin
  Val(Edit1.Text,value,code);
  Edit1.Text := formatfloat('#.0', T);

end;

end.

Answer 1

Do not compare the captions because you will have magic values in your code.

Declare a ValueObject containing the Value and the Name

type
  TTensionValue = record
  private
    FValue : Integer;
    FName : string;
  public
    constructor Create( AValue : Integer; const AName : string );
    class function EMPTY : TTensionValue;
    property Value : Integer read FValue;
    property Name : string;
  end;

  TTensionValues = TList<TTensionValue>;

class function TTensionValue.EMPTY : TTensionValue;
begin
  Result.FValue := 0;
  Result.FName := '';
end;

constructor TTensionValue.Create( AValue : Integer; const AName : string );
begin
  // Validation of AValue and AName
  if AName = '' then
    raise Exception.Create( 'AName' );
  if AValue < 0 then
    raise Exception.Create( 'AValue' );

  FValue := AValue;
  FName := AName;
end;

Prepare a List with valid entries

type
  TForm1 = class( TForm )
  ...
    procedure RadioGroup1Click( Sender: TObject );
  private
    FTensions : TTensionValues;
    procedure PopulateTensions( AStrings : TStrings );
  public
    procedure AfterConstruction; override;
    procedure BeforeDestruction; override;
  end;

procedure TForm1.AfterConstruction;
begin
  inherited;
  FTensions := TTensionValues.Create;

  FTensions.Add( TTensionValue.Create( 5, 'Linear Tension' ) );
  FTensions.Add( TTensionValue.Create( 10, 'Non-Linear tension' ) );
end;

procedure TForm1.BeforeDestruction;
begin
  FTenstions.Free;
  inherited;
end;

Populate that list to the RadioGroup

procedure TForm1.PopulateTensions( AStrings : TStrings );
var
  LValue : TTensionValue;
begin
  AStrings.BeginUpdate;
  try
    AStrings.Clear;
    for LValue in FTensions.Count - 1 do
      AStrings.Add( LValue.Name );
  finally
    AStrings.EndUpdate;
  end;
end;

procedure TForm1.FormShow( Sender.TObject );
begin
  PopulateTensions( RadioGroup1.Items );
end;

Now you only ask the TensionList for the value

procedure TForm1.RadioGroup1Click( Sender: TObject );
begin
  T := FTensions[RadioGroup1.ItemIndex].Value;
end;

The selected value now only rely on the chosen ItemIndex and not on the caption text.