在 case 语句中使用字符串

unit Unit1;

interface

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

type
TForm1 = class(TForm)
RadioGroup1: TRadioGroup;
Button1: TButton;
Button2: TButton;
Button3: TButton;
Button4: TButton;
Button5: TButton;
Button6: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
procedure Button4Click(Sender: TObject);
procedure Button5Click(Sender: TObject);
procedure Button6Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

uses TypInfo; {操作枚举用}

{初始化一个单选组, 用于测试}
procedure TForm1.FormCreate(Sender: TObject);
begin
RadioGroup1.Items.CommaText := 'a,bb,ccc,dddd';
RadioGroup1.ItemIndex := 0;
end;

{这是 case 语句比较常规的用法}
procedure TForm1.Button1Click(Sender: TObject);
begin
case RadioGroup1.ItemIndex of
0: Color := clRed;
1: Color := clYellow;
2: Color := clLime;
3: Color := clBlue;
end;
end;

{方法一: 假如要 case 的字符串的长度不同}
procedure TForm1.Button2Click(Sender: TObject);
var
str: string;
begin
str := RadioGroup1.Items[RadioGroup1.ItemIndex];
case Length(str) of
1 : Color := clRed;
2 : Color := clYellow;
3 : Color := clLime;
4 : Color := clBlue;
end;
end;

{方法二: 假如要 case 的字符串的第一个字母不同, case 是支持字符的}
procedure TForm1.Button3Click(Sender: TObject);
var
str: string;
begin
str := RadioGroup1.Items[RadioGroup1.ItemIndex];
case str[1] of
'a': Color := clRed;
'b': Color := clYellow;
'c': Color := clLime;
'd': Color := clBlue;
end;
end;

{方法三: 借用 TStringList}
procedure TForm1.Button4Click(Sender: TObject);
var
List: TStringList;
str: string;
begin
List := TStringList.Create;
List.Text := RadioGroup1.Items.Text;

str := RadioGroup1.Items[RadioGroup1.ItemIndex];
case List.IndexOf(str) of
0: Color := clRed;
1: Color := clYellow;
2: Color := clLime;
3: Color := clBlue;
end;

List.Free;
end;

{方法四: 借用枚举}
type
TMyEnum = (a, bb, ccc, dddd);

procedure TForm1.Button5Click(Sender: TObject);
var
MyEnum: TMyEnum;
str: String;
begin
str := RadioGroup1.Items[RadioGroup1.ItemIndex];

MyEnum := TMyEnum(GetEnumvalue(TypeInfo(TMyEnum), str));
case MyEnum of
a    : Color := clRed;
bb   : Color := clYellow;
ccc  : Color := clLime;
dddd : Color := clBlue;
end;
end;

{方法五: 利用对比字符串返回的整数, 这种方法并不太可靠, 但在某种情况下会更灵活}
procedure TForm1.Button6Click(Sender: TObject);
var
str: string;
begin
str := RadioGroup1.Items[RadioGroup1.ItemIndex];
case CompareStr(str, 'a') of
0: Color := clRed;
1: Color := clYellow;
2: Color := clLime;
3: Color := clBlue;
end;
end;

end.

object Form1: TForm1
Left = 0
Top = 0
Caption = 'Form1'
ClientHeight = 111
ClientWidth = 265
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
Position = poDesktopCenter
OnCreate = FormCreate
PixelsPerInch = 96
TextHeight = 13
object Button1: TButton
Left = 16
Top = 15
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 97
Top = 15
Width = 75
Height = 25
Caption = 'Button2'
TabOrder = 1
OnClick = Button2Click
end
object Button3: TButton
Left = 16
Top = 46
Width = 75
Height = 25
Caption = 'Button3'
TabOrder = 2
OnClick = Button3Click
end
object RadioGroup1: TRadioGroup
Left = 178
Top = 8
Width = 80
Height = 94
Caption = 'RadioGroup1'
TabOrder = 3
end
object Button4: TButton
Left = 97
Top = 46
Width = 75
Height = 25
Caption = 'Button4'
TabOrder = 4
OnClick = Button4Click
end
object Button5: TButton
Left = 16
Top = 77
Width = 75
Height = 25
Caption = 'Button5'
TabOrder = 5
OnClick = Button5Click
end
object Button6: TButton
Left = 97
Top = 77
Width = 75
Height = 25
Caption = 'Button6'
TabOrder = 6
OnClick = Button6Click
end
end