Search code examples
delphipascallazarus

How to get the object of a TList in a TList?

Assume that I have a multiple objects stored in TO1 : TList then I create multiple TO1 and put all of them in TO2: TList. How can I get the value of selected object in a selected TO1 within TO2 ?

Solution

  • Since TList gives you pointers for each item, you have to cast the items to the proper datatypes:

    var
  aList: TList;
  aItem: TMyObject;
begin

  aList := TList(TO2[selectedO2Index]);       // this cast isn't really needed
  aItem := TMyObject(aList[selectedO1Index]); // neither this one!

end;

    You can save one variable by doing like this:

    var
  aItem: TMyObject;
begin

  // Now the cast to TList is needed!
  aItem := TMyObject(TList(TO2[selectedO2Index])[selectedO1Index]);

end;

    Depending on the Delphi version you are using, it would be more comfortable to use either TList<T> or TObjectList<T> generic class. No casts will be needed!