在 case 语句中使用字符串

非常遗憾 Delphi 的 case 语句不支持字符串, 但我觉得这也可能是基于效率的考量;
如果非要在 case 中使用字符串, 也不是不可以变通, 这里提供了五种方法.

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