如何使用字符串索引属性？

Question

我有这样的代码：

type 
    TMyClass = class 
    private 
     procedure SetKeyValue(const Key: WideString; Value: Widestring); 
     function GetKeyValue(const Key: WideString): WideString; 
    public 
     // this works 
     property KeyValue[const Index: WideString] : WideString read GetKeyValue write SetKeyValue; 

     // this does not compile 
     // [Error]: Incompatible types: 'String' and 'Integer' 
     property Speed: WideString index 'SPEED' read GetKeyValue write SetKeyValue; 
    end; 

的Speed财产给我的错误：

Incompatible types: 'String' and 'Integer'

我需要的索引是字符串。 是否可以使用带有字符串值的index？

Answer 1

这是不可能的。索引属性仅支持整数作为索引常量。

见documentation（各有侧重）：

Index specifiers allow several properties to share the same access method while representing different values. An index specifier consists of the directive index followed by an integer constant between -2147483647 and 2147483647. If a property has an index specifier, its read and write specifiers must list methods rather than fields.

Answer 2

这是根本不可能与index符，因为它仅支持完整的索引。你将不得不使用一个单独的一套属性的getter/setter方法：

type 
    TMyClass = class 
    private 
    ... 
    procedure SetSpeed(const Value: WideString); 
    function GetSpeed: WideString; 
    public 
    ... 
    property Speed: WideString read GetSpeed write SetSpeed; 
    end; 

procedure TMyClass.SetSpeed(const Value: WideString); 
begin 
    KeyValue['SPEED'] := Value; 
end; 

function TMyClass.GetSpeed: WideString; 
begin 
    Result := KeyValue['SPEED']; 
end; 

Answer 3

它非常好

属性值[常量名称：字符串]：串读的GetValue写的SetValue;

{ClassName=class} 
private 
fArrayKey: Array of String;{1} 
fArrayValue: Array of String;{2} 
procedure Add(const Name, Value: string); 
function GetValue(const Name: string): string; 
procedure SetValue(const Name, Value: string); 
published 
property Values[const Name: string{1}]: string{2} read GetValue write SetValue; 

---

function {ClassName.}GetValue(const Name: string): string; 
Var I:integer; 
Begin 
Result := '#empty'; 
    for I := low(fArrayKey) to high(fArrayKey) do 
    if fArrayKey[i]=Name then 
     Begin 
     Result := fArrayValue[i]; 
     Break 
     End; 
If result='#empty' the Raise Exception.CreateFmt('Key %s not found',[name]); 
End; 
procedure {ClassName.}SetValue(const Name, Value: string); 
var i,j:integer 
Begin 
j:=-1; 
    for I := low(fArrayKey) to high(fArrayKey) do 
    if fArrayKey[i]=Name then 
     Begin 
     j:= i; 
     Break 
     End; 
If j=-1 then Add(name,value) else fArrayValue[i]:= Value; 
End; 
procedure {ClassName.}Add(const Name, Value: string); 
begin 
    SetLength(fArrayKey,Length(fArrayKey)+1); 
    SetLength(fArrayValue,Length(fArrayValue)+1); 
    fArrayKey [Length(fArrayKey) -1] := Name; 
    fArrayValue[Length(fArrayValue)-1] := Value; 
end; 

http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Properties_(Delphi)