在TObjectDictionary中使用对象作为键 [英] Use objects as keys in TObjectDictionary

问题描述

当我使用TObjectDictionary，TKey是对象的时候，我的应用程序工作不正确。
我有两个单位，它们包含两个类。第一单位：

When I use TObjectDictionary, where TKey is object, my application work uncorrectly. I have two units, thats contain two classes. First unit:

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！

推荐答案

字典取决于键值。您正在密钥中存储对象的引用。如果您创建两个相同的对象，具有不同的值，因此具有不同的键。

A Dictionary depends on a key value. You are storing a reference to an object in the key. If you create two objects that are setup identically the have different values and hence different keys.

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，您可以在TObjectDictonary中使用基于RubricName和TermName的String作为First Type参数。这样你就可以得到相同的值。

Instead you could uses a String as the First Type Parameter in the TObjectDictonary that is based on RubricName and TermName. With this you would then get back the same value.

还应该注意的是，XE2中的代码创建了两个内存泄漏。创建的每个对象都必须被释放。因此这段代码也是泄漏记忆

It should also be noted, that above code in XE2 creates two memory leaks. Every object created must be freed. Hence this section of code also is leaking memory

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

给出所有这些。如果你想使用一个对象作为一个关键，你可以使用自定义平等比较器。这是您的示例更改为实现 IEqualityComparer< T> ，并修复了一些内存泄漏。

Given all of that. If you want to use an Object as a Key you can do it with a Custom Equality Comparer. Here is your example changed to implement IEqualityComparer<T>, and fix a few memory leaks.

unit ClassificationMatrix;

interface

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

type
TClassificationMatrix = class(TObject)
  private
    FTable: TObjectDictionary<TRubTerm, 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: 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);
  try
   if Not FTable.TryGetValue(ARubTerm, Result) then
      result := 0;
  finally
    ARubTerm.Free;
  end;
end;

end.

和RubTerm.pas单元

And the RubTerm.pas unit

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.

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