访问TDictionary项目

Question

I am testing the TDictionary using the embarcadero sample ( http://docwiki.embarcadero.com/CodeExamples/XE5/en/Generics_Collections_TDictionary_%28Delphi%29 )

No problem for creating and adding key and value. However, when I try to access the table using key value 'London':

(1) Dictionary.Items['London'].Country -> gives the correct value "Dictionary.Items['London'].Country'

(2) input 'London' in Edit1.Text, then Dictionary.Items[Edit1.Text].Country -> gives error "the item not found'?

Could someone explain this?

Thanks in advance.

//////////////////////////////////// /// sample code

var Dictionary: TDictionary<String, TCity>;
    City, Value: TCity;
    Key: String;


begin
  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);

  showmessage(Dictionary.Items['London'].Country); // This One is OK

  // now using Edit1.Text where I put 'London'
  Showmessage(Dictionary.Items[Edit1.Text].Country); // This return to error message (Item not found)


  Dictionary.Clear;
  Dictionary.Free;
  City.Free;

end;

Answer 1

The explanation is that, contrary to what you claim, Edit1.Text does not equal 'London' . Perhaps the letter case does not match. Or there is leading or trailing whitespace.

Add an assertion to verify that I am correct:

Assert(Edit1.Text='London');