{"id":1704,"date":"2015-01-08T17:50:05","date_gmt":"2015-01-08T09:50:05","guid":{"rendered":"http:\/\/blog.qdac.cc\/?p=1704"},"modified":"2015-01-08T17:50:24","modified_gmt":"2015-01-08T09:50:24","slug":"delphi-%e4%b8%ad%e8%87%aa%e5%ae%9a%e4%b9%89-variant-%e7%b1%bb%e5%9e%8b%e6%8e%a5%e5%8f%a3","status":"publish","type":"post","link":"https:\/\/blog.qdac.cc\/?p=1704","title":{"rendered":"Delphi \u4e2d\u81ea\u5b9a\u4e49 Variant \u7c7b\u578b\u5b9e\u73b0\u65b9\u5f0f"},"content":{"rendered":"<p>Delphi \u4e2d\uff0c\u5bf9 Variant \u7c7b\u578b\u8fdb\u884c\u4e86\u589e\u5f3a\uff0c\u652f\u6301\u4e86\u81ea\u5df1\u7684 UnicodeString \u3001 AnsiString \u548c TBcd\uff0c\u90a3\u4e48\u6709\u4eba\u53ef\u80fd\u5947\u602a\u5b83\u662f\u600e\u4e48\u5b8c\u6210\u8fd9\u4e00\u652f\u6301\u7684\u5462\uff1f\u79d8\u5bc6\u5c31\u5728\u00a0TCustomVariantType \u8fd9\u4e2a\u7c7b\u578b\u3002<\/p>\n<p>\u6211\u4eec\u770b Variants \u5355\u5143\u5bf9\u5176\u5b9a\u4e49\uff1a<\/p>\n<pre class=\"lang:delphi decode:true \">TCustomVariantType = class(TObject, IInterface)\r\n  private\r\n    FVarType: TVarType;\r\n  protected\r\n    { IInterface }\r\n    function QueryInterface(const IID: TGUID; out Obj): HResult; virtual; stdcall;\r\n    function _AddRef: Integer; stdcall;\r\n    function _Release: Integer; stdcall;\r\n\r\n    procedure SimplisticClear(var V: TVarData);\r\n    procedure SimplisticCopy(var Dest: TVarData; const Source: TVarData;\r\n      const Indirect: Boolean = False);\r\n\r\n    procedure RaiseInvalidOp;\r\n    procedure RaiseCastError;\r\n    procedure RaiseDispError;\r\n\r\n    function LeftPromotion(const V: TVarData; const Operator: TVarOp;\r\n      out RequiredVarType: TVarType): Boolean; virtual;\r\n    function RightPromotion(const V: TVarData; const Operator: TVarOp;\r\n      out RequiredVarType: TVarType): Boolean; virtual;\r\n    function OlePromotion(const V: TVarData;\r\n      out RequiredVarType: TVarType): Boolean; virtual;\r\n    procedure DispInvoke(Dest: PVarData; [Ref] const Source: TVarData;\r\n      CallDesc: PCallDesc; Params: Pointer); virtual;\r\n\r\n    procedure VarDataInit(var Dest: TVarData);\r\n    procedure VarDataClear(var Dest: TVarData);\r\n\r\n    procedure VarDataCopy(var Dest: TVarData; const Source: TVarData);\r\n    procedure VarDataCopyNoInd(var Dest: TVarData; const Source: TVarData);\r\n\r\n    procedure VarDataCast(var Dest: TVarData; const Source: TVarData);\r\n    procedure VarDataCastTo(var Dest: TVarData; const Source: TVarData;\r\n      const AVarType: TVarType); overload;\r\n    procedure VarDataCastTo(var Dest: TVarData; const AVarType: TVarType); overload;\r\n    procedure VarDataCastToOleStr(var Dest: TVarData);\r\n\r\n    procedure VarDataFromStr(var V: TVarData; const Value: string);\r\n{$IFNDEF NEXTGEN}\r\n    procedure VarDataFromOleStr(var V: TVarData; const Value: WideString);\r\n    procedure VarDataFromLStr(var V: TVarData; const Value: AnsiString);\r\n{$ENDIF !NEXTGEN}\r\n    function VarDataToStr(const V: TVarData): string;\r\n\r\n    function VarDataIsEmptyParam(const V: TVarData): Boolean;\r\n    function VarDataIsByRef(const V: TVarData): Boolean;\r\n    function VarDataIsArray(const V: TVarData): Boolean;\r\n\r\n    function VarDataIsOrdinal(const V: TVarData): Boolean;\r\n    function VarDataIsFloat(const V: TVarData): Boolean;\r\n    function VarDataIsNumeric(const V: TVarData): Boolean;\r\n    function VarDataIsStr(const V: TVarData): Boolean;\r\n  public\r\n    constructor Create; overload;\r\n    constructor Create(RequestedVarType: TVarType); overload;\r\n    destructor Destroy; override;\r\n    property VarType: TVarType read FVarType;\r\n\r\n    function IsClear(const V: TVarData): Boolean; virtual;\r\n    procedure Cast(var Dest: TVarData; const Source: TVarData); virtual;\r\n    procedure CastTo(var Dest: TVarData; const Source: TVarData;\r\n      const AVarType: TVarType); virtual;\r\n    procedure CastToOle(var Dest: TVarData; const Source: TVarData); virtual;\r\n\r\n    \/\/ The following two procedures must be overridden by your custom\r\n    \/\/  variant type class.  Simplistic versions of Clear and Copy are\r\n    \/\/  available in the protected section of this class but depending on the\r\n    \/\/  type of data contained in your custom variant type those functions\r\n    \/\/  may not handle your situation.\r\n    procedure Clear(var V: TVarData); virtual; abstract;\r\n    procedure Copy(var Dest: TVarData; const Source: TVarData;\r\n      const Indirect: Boolean); virtual; abstract;\r\n\r\n    procedure BinaryOp(var Left: TVarData; const Right: TVarData;\r\n      const Operator: TVarOp); virtual;\r\n    procedure UnaryOp(var Right: TVarData; const Operator: TVarOp); virtual;\r\n    function CompareOp(const Left, Right: TVarData;\r\n      const Operator: TVarOp): Boolean; virtual;\r\n    procedure Compare(const Left, Right: TVarData;\r\n      var Relationship: TVarCompareResult); virtual;\r\n  end;<\/pre>\n<p>\u8981\u5b9e\u73b0\u81ea\u5df1\u7684 Variant \u7c7b\u578b\uff0c\u9700\u8981\u505a\u7684\u5c31\u662f\u7ee7\u627f\u5e76\u91cd\u8f7d\u5b83\u3002\u5982\u679c\u8981\u4e86\u89e3\u8fdb\u4e00\u6b65\u7684\u8be6\u7ec6\u5b9e\u73b0\u65b9\u6cd5\uff0c\u53ef\u4ee5\u53c2\u8003 fmtbcd.pas \u91cc\u5bf9\u00a0TFMTBcdVariantType \u7c7b\u578b\u7684\u5b9e\u73b0\u3002<\/p>\n<pre class=\"lang:delphi decode:true\">\/\/variants.pas\r\nTInvokeableVariantType = class(TCustomVariantType, IVarInvokeable)\r\n  protected\r\n    function FixupIdent(const AText: string): string; virtual;\r\n    procedure DispInvoke(Dest: PVarData; [Ref] const Source: TVarData;\r\n      CallDesc: PCallDesc; Params: Pointer); override;\r\n  public\r\n    { IVarInvokeable }\r\n    function DoFunction(var Dest: TVarData; const V: TVarData;\r\n      const Name: string; const Arguments: TVarDataArray): Boolean; virtual;\r\n    function DoProcedure(const V: TVarData; const Name: string;\r\n      const Arguments: TVarDataArray): Boolean; virtual;\r\n    function GetProperty(var Dest: TVarData; const V: TVarData;\r\n      const Name: string): Boolean; virtual;\r\n    function SetProperty(const V: TVarData; const Name: string;\r\n      const Value: TVarData): Boolean; virtual;\r\n  end;\r\n\/\/typinfo.pas\r\nTPublishableVariantType = class(TInvokeableVariantType, IVarInstanceReference)\r\n  protected\r\n    { IVarInstanceReference }\r\n    function GetInstance(const V: TVarData): TObject; virtual; abstract;\r\n  public\r\n    function GetProperty(var Dest: TVarData; const V: TVarData;\r\n      const Name: string): Boolean; override;\r\n    function SetProperty(const V: TVarData; const Name: string;\r\n      const Value: TVarData): Boolean; override;\r\n  end;\r\n\/\/fmtbcd.pas\r\nTFMTBcdVariantType = class(TPublishableVariantType)\r\n  protected\r\n    function GetInstance(const V: TVarData): TObject; override;\r\n  public\r\n    procedure Clear(var V: TVarData); override;\r\n    procedure Copy(var Dest: TVarData; const Source: TVarData; const Indirect: Boolean); override;\r\n    procedure Cast(var Dest: TVarData; const Source: TVarData); override;\r\n    procedure CastTo(var Dest: TVarData; const Source: TVarData; const AVarType: TVarType); override;\r\n    procedure BinaryOp(var Left: TVarData; const Right: TVarData; const Operator: TVarOp); override;\r\n    procedure Compare(const Left, Right: TVarData; var Relationship: TVarCompareResult); override;\r\n  end;<\/pre>\n<p>\u66f4\u8be6\u7ec6\u7684\u5206\u6790\u6211\u5c31\u4e0d\u591a\u9610\u8ff0\u4e86\uff0c\u4ee3\u7801\u662f\u7a0b\u5e8f\u5458\u6700\u597d\u7684\u8001\u5e08\uff0c\u662f\u6700\u51c6\u786e\u7684\u8868\u8ff0\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Delphi \u4e2d\uff0c\u5bf9 Variant \u7c7b [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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