delphi – 在TObjectDictionary中使用对象作为键

当我使用TObjectDictionary时,TKey是对象,我的应用程序工作不正确.
我有两个单元,它包含两个类.第一单元：

unit RubTerm;

interface

type
  TRubTerm = Class(TObject)
  private
    FRubricName: String;
    FTermName: String;
  public
    property RubricName: String read FRubricName;
    property TermName: String read FTermName;
    constructor Create(ARubricName,ATermName: String);
  end;

implementation

constructor TRubTerm.Create(ARubricName,ATermName: String);
begin
  Self.FRubricName := ARubricName;
  Self.FTermName := ATermName;
end;

end;

第二单元：

unit ClassificationMatrix;

interface

uses
  System.Generics.Collections,System.Generics.Defaults,System.SysUtils,RubTerm;

type
TClassificationMatrix = class(TObject)
  private
    FTable: TObjectDictionary<TRubTerm,Integer>;
  public
    constructor Create;
    procedure TClassificationMatrix.AddCount(ADocsCount: Integer; ARubName,ATermName: String);
    function TClassificationMatrix.GetCount(ARubName,ATermName: String): Integer;
  end;

implementation

constructor TClassificationMatrix.Create;
begin
  FTable := TObjectDictionary<TRubTerm,Integer>.Create;
end;

procedure TClassificationMatrix.AddCount(ADocsCount: Integer; ARubName,ATermName: String);
var
  ARubTerm: TRubTerm;
begin
  ARubTerm := TRubTerm.Create(ARubName,ATermName);
  FTable.Add(ARubTerm,ADocsCount);
end;

function TClassificationMatrix.GetCount(ARubName,ATermName: String): Integer;
var
  ARubTerm: TRubTerm;
begin
  ARubTerm := TRubTerm.Create(ARubName,ATermName);
  FTable.TryGetValue(ARubTerm,Result);
end;

end;

但是这段代码工作不正常：

procedure TestTClassificationMatrix.TestGetCount;
var
  DocsCountTest: Integer;
begin
  FClassificationMatrix.AddCount(10,'R','T');
  DocsCountTest := FClassificationMatrix.GetCount('R','T');
end;
// DocsCountTest = 0! Why not 10? Where is problem?

谢谢！

解决方法

字典取决于键值.您正在存储对键中对象的引用.如果您创建两个设置相同的对象,则具有不同的值,因此具有不同的键.

var
  ARubTerm1: TRubTerm;
  ARubTerm2: TRubTerm;
begin
  ARubTerm1 := TRubTerm.Create('1','1');
  ARubTerm2 := TRubTerm.Create('1','1');
 //  ARubTerm1 = ARubTerm2 is not possible here as ARubTerm1 points to a different address than ARubTerm2
end;

相反,您可以使用String作为TObjectDictonary中的第一个类型参数,该参数基于RubricName和TermName.有了这个,你就可以得到相同的价值.

还应该注意,XE2中的上述代码会产生两个内存泄漏.必须释放创建的每个对象.因此这部分代码也是泄漏内存

function TClassificationMatrix.GetCount(ARubName,Result);
end;

鉴于所有这些.如果要将Object用作Key,可以使用Custom Equality Comparer执行此操作.以下是您的示例已更改为实现IEqualityComparer< T>,并修复了一些内存泄漏.

unit ClassificationMatrix;

interface

uses
  Generics.Collections,Generics.Defaults,SysUtils,Integer>;
  public
    constructor Create;
    procedure AddCount(ADocsCount: Integer; ARubName,ATermName: String);
    function GetCount(ARubName,ATermName: String): Integer;
  end;

implementation

constructor TClassificationMatrix.Create;
var
 Comparer : IEqualityComparer<RubTerm.TRubTerm>;
begin
  Comparer := TRubTermComparer.Create;
  FTable := TObjectDictionary<TRubTerm,Integer>.Create([doOwnsKeys],TRubTermComparer.Create);
end;

procedure TClassificationMatrix.AddCount(ADocsCount: Integer; ARubName,ATermName);
  try
   if Not FTable.TryGetValue(ARubTerm,Result) then
      result := 0;
  finally
    ARubTerm.Free;
  end;
end;

end.

还有RubTerm.pas单元

unit RubTerm;

interface
uses Generics.Defaults;

type
  TRubTerm = Class(TObject)
  private
    FRubricName: String;
    FTermName: String;
  public
    property RubricName: String read FRubricName;
    property TermName: String read FTermName;
    constructor Create(ARubricName,ATermName: String);
    function GetHashCode: Integer; override;
  end;

  TRubTermComparer = class(TInterfacedObject,IEqualityComparer<TRubTerm>)
  public
    function Equals(const Left,Right: TRubTerm): Boolean;
    function GetHashCode(const Value: TRubTerm): Integer;
  end;


implementation

constructor TRubTerm.Create(ARubricName,ATermName: String);
begin
  Self.FRubricName := ARubricName;
  Self.FTermName := ATermName;
end;


{ TRubTermComparer }

function TRubTermComparer.Equals(const Left,Right: TRubTerm): Boolean;
begin
  result := (Left.RubricName = Right.RubricName) and (Left.TermName = Right.TermName);
end;

function TRubTermComparer.GetHashCode(const Value: TRubTerm): Integer;
begin
  result := Value.GetHashCode;
end;

//The Hashing code was taken from David's Answer to make this a complete answer.    
{$IFOPT Q+}
  {$DEFINE OverflowChecksEnabled}
  {$Q-}
{$ENDIF}
function CombinedHash(const Values: array of Integer): Integer;
var
  Value: Integer;
begin
  Result := 17;
  for Value in Values do begin
    Result := Result*37 + Value;
  end;
end;
{$IFDEF OverflowChecksEnabled}
  {$Q+}
{$ENDIF}

function GetHashCodeString(const Value: string): Integer;
begin
  Result := BobJenkinsHash(PChar(Value)^,SizeOf(Char) * Length(Value),0);
end;

function TRubTerm.GetHashCode: Integer;

begin
  Result := CombinedHash([GetHashCodeString(Value.RubricName),GetHashCodeString(Value.TermName)]);    
end;

end.