原本一直使用 TList， 将定义的一个个 Record 保存在TList 里面， 为了能把某些对象管理起来， 例如一个类的 n 多实例，可以进行索引、查找、释放等

今天刚看到原来已经有了一个叫 TDictionary 对象，用起来挺方便。 挺像我们在DB中定义的 Dictionary 表，Key、Value。  而那个不管Key、Value 都挺发达，允许各种定义的类。 

ok，下面官方Demo很通俗易懂，各方法都在：

type  TCity = class    Country: String;    Latitude: Double;    Longitude: Double;  end; const  EPSILON = 0.0000001; var  Dictionary: TDictionary<String, TCity>;  City, Value: TCity;  Key: String; begin  { Create the dictionary. }  Dictionary := TDictionary<String, TCity>.Create;  City := TCity.Create;  { Add some key-value pairs to the dictionary. }  City.Country := ‘Romania‘;  City.Latitude := 47.16;  City.Longitude := 27.58;  Dictionary.Add(‘Iasi‘, City);   City := TCity.Create;  City.Country := ‘United Kingdom‘;  City.Latitude := 51.5;  City.Longitude := -0.17;  Dictionary.Add(‘London‘, City);   City := TCity.Create;  City.Country := ‘Argentina‘;  { Notice the wrong coordinates }  City.Latitude := 0;  City.Longitude := 0;  Dictionary.Add(‘Buenos Aires‘, City);   { Display the current number of key-value entries. }  writeln(‘Number of pairs in the dictionary: ‘ +  IntToStr(Dictionary.Count));   // Try looking up "Iasi".  if (Dictionary.TryGetValue(‘Iasi‘, City) = True) then  begin    writeln(    ‘Iasi is located in ‘ + City.Country +    ‘ with latitude = ‘ + FloatToStrF(City.Latitude, ffFixed, 4, 2) +    ‘ and longitude = ‘ + FloatToStrF(City.Longitude, ffFixed, 4, 2)    );  end  else    writeln(‘Could not find Iasi in the dictionary‘);   { Remove the "Iasi" key from dictionary. }  Dictionary.Remove(‘Iasi‘);   { Make sure the dictionary‘s capacity is set to the number of entries. }  Dictionary.TrimExcess;   { Test if "Iasi" is a key in the dictionary. }  if Dictionary.ContainsKey(‘Iasi‘) then    writeln(‘The key "Iasi" is in the dictionary.‘)  else    writeln(‘The key "Iasi" is not in the dictionary.‘);   { Test how (United Kingdom, 51.5, -0.17) is a value in the dictionary but    ContainsValue returns False if passed a different instance of TCity with the    same data, as different instances have different references. }  if Dictionary.ContainsKey(‘London‘) then  begin    Dictionary.TryGetValue(‘London‘, City);    if (City.Country = ‘United Kingdom‘) and (CompareValue(City.Latitude, 51.5, EPSILON) = EqualsValue) and (CompareValue(City.Longitude, -0.17, EPSILON) = EqualsValue) then      writeln(‘The value (United Kingdom, 51.5, -0.17) is in the dictionary.‘)    else      writeln(‘Error: The value (United Kingdom, 51.5, -0.17) is not in the dictionary.‘);    City := TCity.Create;    City.Country := ‘United Kingdom‘;    City.Latitude := 51.5;    City.Longitude := -0.17;    if Dictionary.ContainsValue(City) then      writeln(‘Error: A new instance of TCity with values (United Kingdom, 51.5, -0.17) matches an existing instance in the dictionary.‘)    else      writeln(‘A new instance of TCity with values (United Kingdom, 51.5, -0.17) does not match any existing instance in the dictionary.‘);    City.Free;  end  else    writeln(‘Error: The key "London" is not in the dictionary.‘);   { Update the coordinates to the correct ones. }  City := TCity.Create;  City.Country := ‘Argentina‘;  City.Latitude := -34.6;  City.Longitude := -58.45;  Dictionary.AddOrSetValue(‘Buenos Aires‘, City);   { Generate the exception "Duplicates not allowed". }  try    Dictionary.Add(‘Buenos Aires‘, City);  except    on Exception do      writeln(‘Could not add entry. Duplicates are not allowed.‘);  end;   { Display all countries. }  writeln(‘All countries:‘);  for Value in Dictionary.Values do    writeln(Value.Country);   { Iterate through all keys in the dictionary and display their coordinates. }  writeln(‘All cities and their coordinates:‘);  for Key in Dictionary.Keys do  begin    writeln(Key + ‘: ‘ + FloatToStrF(Dictionary.Items[Key].Latitude, ffFixed, 4, 2) + ‘, ‘ +    FloatToStrF(Dictionary.Items[Key].Longitude, ffFixed, 4, 2));  end;   { Clear all entries in the dictionary. }  Dictionary.Clear;   { There should be no entries at this point. }  writeln(‘Number of key-value pairs in the dictionary after cleaning: ‘ + IntToStr(Dictionary.Count));   { Free the memory allocated for the dictionary. }  Dictionary.Free;  City.Free;  readln;end.

使用 Delphi Xe 的 TDictionary