Using Delphi Xe's tdictionary

Originally used TList, the definition of a Record is stored in the TList, in order to be able to manage some objects, such as a class of n multiple instances, can be indexed, find, release, etc.

Today just saw the original has a call Tdictionary object, use it very convenient.  Pretty much like the Dictionary table we defined in db, Key, Value. And that regardless of key, Value is quite developed, allowing a variety of definitions of the class.

OK, the following official demo is very easy to understand, the methods are:

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:=' 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)ThenBeginWriteln(' Iasi is located in '+ City.Country+' With latitude = '+Floattostrf(City.Latitude, fffixed,4,2)+' and longitude = '+Floattostrf(City.Longitude, fffixed,4,2));EndElseWriteln(' Could not find Iasi in the dictionary ');{Remove the "Iasi" Key from Dictionary.} Dictionary.Remove(' Iasi ');{Make sure the dictionary ' s capacity are set to the number of entries.} Dictionary.TrimExcess;{Test If "Iasi" is a key in the dictionary.}If Dictionary.ContainsKey(' Iasi ')ThenWriteln(' The key ' Iasi ' is in the dictionary. ')ElseWriteln(' The key ' Iasi ' is not in the dictionary. ');{Test How (Kingdom, 51.5, -0.17) are a value in the dictionary but Containsvalue returns False if passed a differen T instance of tcity with the same data, as different instances has different references. }If Dictionary.ContainsKey(' London ')ThenBegin Dictionary.TryGetValue(' London ', City);If(City.Country=' Kingdom ')and(CompareValue(City.Latitude,51.5, EPSILON)= Equalsvalue)and(CompareValue(City.Longitude,-0.17, EPSILON)= Equalsvalue)ThenWriteln(' The value (kingdom, 51.5, -0.17) is in the dictionary. ')ElseWriteln(' Error:the value (kingdom, 51.5, -0.17) is not in the dictionary. '); City:= Tcity.Create; City.Country:=' Kingdom '; City.Latitude:=51.5; City.Longitude:=-0.17;If Dictionary.Containsvalue(City)ThenWriteln(' Error:a new instance of tcity with values (for Kingdom, 51.5, -0.17) matches an existing instance in the dictionary. ')ElseWriteln(' A new instance of tcity with values (for Kingdom, 51.5, -0.17) does not match any existing instance in the dictionary. ‘); City.Free;EndElseWriteln(' 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);ExceptOn ExceptionDoWriteln(' Could not add entry. Duplicates is not allowed. ');End;{Display all countries.}Writeln(' All countries: ');For ValueIn Dictionary.ValuesDoWriteln(Value.Country);{Iterate through all keys in the dictionary and display their coordinates.}Writeln(' All cities and their coordinates: ');For KeyIn Dictionary.KeysDoBeginWriteln(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 is 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. Freereadln; End              

Using the tdictionary of Delphi Xe