如何将属性与字符串索引一起使用？

Question

我有这个代码：

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;

Speed 属性给我错误：

Incompatible types: 'String' and 'Integer'

我需要索引为字符串。是否可以将 index 与字符串值一起使用？

Answer 1

那是不可能的。索引属性仅支持整数作为索引常量。

见documentation（自己强调）：

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

这对于 index 说明符来说根本不可能，因为它只支持整数索引。您将不得不使用一组单独的属性 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

效果很好

属性 Values[const Name: string]: string read GetValue write 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)

如何将属性与字符串索引一起使用？

How to use property with string index?

delphi

delphi-7

如何将 属性 与字符串索引一起使用？

How to use property with string index?

delphi

delphi-7

如何将属性与字符串索引一起使用？