Delphi, adding digets | 易学教程

问题

My textbook says I need to make a donation program with three buttons, each representing a certain amount of money. The "Amount donated" should be shown on a label after I press a button.

For instance if I press the $10 button, it will say The total amount raised so far is $10. And then if I press the $50 button, the label should caption The total amount raised so far is $60. I'm in need of 3 buttons, a $10, $20 and $50.

I don't even know where to start with the coding side!

Here's the starting code:

unit AIDSAWARENESS_U;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    btn10: TButton;
    btn50: TButton;
    btn20: TButton;
    lblOutput: TLabel;
  private
   {private declarations}
  public
   {public declarations}
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}


end.

If you wouldn't mind helping me, it would be much appreciated!

回答1:

Try this:

unit AIDSAWARENESS_U;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    btn10: TButton;
    btn50: TButton;
    btn20: TButton;
    lblOutput: TLabel;
    procedure btnClick(Sender: TObject);
  private
    {private declarations}
    Amount: Integer;
  public
    {public declarations}
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.btnClick(Sender: TObject);
begin
  Inc(Amount, TButton(Sender).Tag);
  lblOutput.Caption := Format('The total amount raised so far is $%d', [Amount]);
end;

end.

Then all you have to do is assign btnClick() as the OnClick event handler for all three buttons, and set each button's Tag property to the desired amount.

回答2:

Your application has to

contain 3 buttons with different values (let them name Value10_Button, Value20_Button and Value30_Button)
contain a label with the current amount (let it name Amount_Label)
RaiseAmount if one of the value button is pressed
UpdateAmount_Label if the amount value has changed

Following this we got straight to

type
  TForm1 = class( TForm )
    Value10_Button : TButton;
    Value20_Button : TButton;
    Value50_Button : TButton;
    Amount_Label : TLabel;
    procedure Value10_ButtonClick( Sender : TObject );
    procedure Value20_ButtonClick( Sender : TObject );
    procedure Value50_ButtonClick( Sender : TObject );
  private
    FAmount : Currency;
    procedure SetAmount( const Value : Currency );
    procedure UpdateAmount_Label;
    procedure RaiseAmount( const Value : Currency );
  public
    property Amount : Currency read FAmount write SetAmount;
  end;

procedure TForm1.RaiseAmount( const Value : Currency );
begin
  Amount := Amount + Value;
end;

procedure TForm1.SetAmount( const Value : Currency );
begin
  if FAmount <> Value then
  begin
    FAmount := Value;
    UpdateAmount_Label;
  end;
end;

procedure TForm1.UpdateAmount_Label;
begin
  Amount_Label.Caption := Format( 'The total amount raised so far is $%f', [Amount] );
end;

procedure TForm1.Value10_ButtonClick( Sender : TObject );
begin
  RaiseAmount( 10 );
end;

procedure TForm1.Value20_ButtonClick( Sender : TObject );
begin
  RaiseAmount( 20 );
end;

procedure TForm1.Value50_ButtonClick( Sender : TObject );
begin
  RaiseAmount( 50 );
end;

As suggested by Remy you can use the Tagproperty of the Buttons, but I prefer to use them in a different way

procedure TForm1.Value_ButtonClick( Sender : TObject );
begin
  case ( Sender as TComponent ).Tag of
    1 : RaiseAmount( 10 );
    2 : RaiseAmount( 20 );
    3 : RaiseAmount( 30 );
  end;
end;

In a real application I would have a lookup table to get the values from the tag property to get rid of that magic numbers

procedure TForm1.Value_ButtonClick( Sender : TObject );
begin
  RaiseAmount( GetAmountFromIndex( ( Sender as TComponent ).Tag ) );
end;

回答3:

You need to

Add a way to count the total value (hint field).
Add event handlers for the buttons, they need to update the value and show the total.

If you don't know how to do that, check your textbook.

来源：https://stackoverflow.com/questions/21721799/delphi-adding-digets

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