AdvancedCharacterControl (Delphi)

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Description

The following example demostrates the use of some advanced method in the Character unit. An edit box is configured to allow 2 unicode characters (since there may be surrogate pairs).

Code

procedure TMainForm.edtCharChange(Sender: TObject);
var
  U4: UCS4Char;
  Cat: TUnicodeCategory;
  Value: String;
begin
  Value := edtChar.Text;

  { Do nothing on empty edit }
  if Value = '' then
    Exit;

  { Note that 2 characters may represent a surrogate pair! }
  { Only allow control codes and alpha-numeric values in }
  if (not IsLetterOrDigit(Value[1])) and
     (not Character.IsControl(Value[1]) and
     (not IsSurrogate(Value[1])))
     then Exit;

  { Covert the entered char to UCS4 }
  U4 := ConvertToUtf32(Value, 1);

  { And now convert back }
  if (ConvertFromUtf32(U4) <> Value) then
    MessageDlg('Cannot happen!', mtError, [mbOK], 0);

  MessageDlg('The numeric value of the character is ' +
    FloatToStr(GetNumericValue(Value[1])), mtInformation, [mbOK], 0);

  { Get the unicode category of the character }
  Cat := GetUnicodeCategory(Value[1]);

  MessageDlg(Format('The character "%s" category is: %s ',
    [Value[1], GetEnumName(TypeInfo(TUnicodeCategory), Ord(Cat))]),
    mtInformation, [mbOK], 0);
end;

procedure TMainForm.FormCreate(Sender: TObject);
begin
  { Allow two characters to be typed into
    the edit box. In case of Unicode surrogates,
    2 characters represent one real character.
  }
  edtChar.MaxLength := 2;
end;

Uses

See Also

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