右滾動文本

Question

我有一個Delphi XE2項目顯示滾動文本（更好的「選框文本」）。 在我的項目中，我有Timer1,Timer2,Button1,Button2,Label1和Label2。 我的目標是在Label1之後顯示一些左滾動文本Button1.Click使用Timer1和一些右滾動文本在Label2之後Button1.Click使用Timer2。

我定義了下面的代碼：

unit Unit1; 

interface 

uses 
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, 
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls; 

type 
    TForm1 = class(TForm) 
    Label1: TLabel; 
    Label2: TLabel; 
    Button1: TButton; 
    Button2: TButton; 
    Timer1: TTimer; 
    Timer2: TTimer; 
    procedure FormCreate(Sender: TObject); 
    procedure Button1Click(Sender: TObject); 
    procedure Button2Click(Sender: TObject); 
    procedure Timer1Timer(Sender: TObject); 
    procedure Timer2Timer(Sender: TObject); 
    private 
    { Private declarations } 
    public 
    { Public declarations } 
    end; 

var 
    Form1: TForm1; 

implementation 

{$R *.dfm} 

procedure TForm1.Button1Click(Sender: TObject); 
begin 
    Timer1.Enabled := true; 
    Timer2.Enabled := true; 
end; 

procedure TForm1.Button2Click(Sender: TObject); 
begin 
    Timer1.Enabled := false; 
    Timer2.Enabled := false; 
end; 

procedure TForm1.FormCreate(Sender: TObject); 
begin 
    Timer1.Interval := 100; 
    Timer2.Interval := 100; 
end; 

procedure TForm1.Timer1Timer(Sender: TObject); 
const 
{$WRITEABLECONST ON} 
    ScrollingText : string = 'This is left scrolling text '; 
{$WRITEABLECONST OFF} 
var 
    ScrollPosition: Integer; 
begin 
    Label1.Caption := ScrollingText; 
    for ScrollPosition := 1 to (Length(ScrollingText) - 1) do 
    begin 
     ScrollingText[ScrollPosition] := Label1.Caption[ScrollPosition + 1]; 
     ScrollingText[Length(ScrollingText)] := Label1.Caption[1]; 
    end; 
end; 

procedure TForm1.Timer2Timer(Sender: TObject); 
const 
{$WRITEABLECONST ON} 
    ScrollingText : string = 'This is right scrolling text '; 
{$WRITEABLECONST OFF} 
var 
    ScrollPosition: Integer; 
begin 
    Label2.Caption := ScrollingText; 
    for ScrollPosition := (Length(ScrollingText) - 1) to 1 do 
    begin 
     ScrollingText[ScrollPosition] := Label2.Caption[ScrollPosition - 1]; 
     ScrollingText[Length(ScrollingText)] := Label2.Caption[1]; 
    end; 
end; 

end.  

我的問題是沒有發生使用Timer2是，Left Scrolling使用Timer1但Right Scrolling發生。

Answer 1

的for環路Timer2Timer應該往下跑，而不是向上：

procedure TForm1.Timer2Timer(Sender: TObject); 
const 
{$WRITEABLECONST ON} 
    ScrollingText : string = 'This is right scrolling text '; 
{$WRITEABLECONST OFF} 
var 
    ScrollPosition: Integer; 
begin 
    Label2.Caption := ScrollingText; 
    for ScrollPosition := (Length(ScrollingText) - 1) downto 2 do 
    begin 
     ScrollingText[ScrollPosition] := Label2.Caption[ScrollPosition - 1]; 
     ScrollingText[1] := Label2.Caption[Length(ScrollingText) - 1]; 
    end; 
end; 

但我建議不要使用可寫的常量，也沒有使用for循環都：

procedure TForm1.FormCreate(Sender: TObject); 
begin 
    ... 
    Label2.Caption := 'This is right scrolling text '; 
end; 

procedure TForm1.Timer2Timer(Sender: TObject); 
var 
    S: String; 
begin 
    S := Label2.Caption; 
    S := S[Length(S)] + Copy(S, 1, Length(S) - 1); 
    Label2.Caption := S; 
end;