search a Generic list

Question

I \'m trouble understanding in modifying the solution from GENERIC SEARCH as my class is more complex and I need to create several different search functions

pro         


        

Answer 1

In your place I would write a subclass of TObjectList and add a custom Search method that would look like this:

TSearchableObjectList = class(TObjectList)
public
  function Search(aFound: TPredicate): T;
end;

The implementation for that method is

function TSearchableObjectList.Search(aFound: TPredicate): T;
var
  item: T;
begin
  for item in Self do
    if aFound(item) then
      Exit(item);
  Result := nil;
end;

An example of this method is

var
  myList: TSearchableObjectList;
  item: TActivitycategory;
  searchKey: string;
begin
  myList := TSearchableObjectList.Create;
  // Here you load your list
  searchKey := 'WantedName';
  // Let´s make it more interesting and perform a case insensitive search,
  // by comparing with SameText() instead the equality operator
  item := myList.Search(function(aItem : TActivitycategory): boolean begin
            Result := SameText(aItem.FirstName, searchKey);
          end);
  // the rest of your code
end;

The TPredicate type used above is declared in SysUtils, so be sure to add it to your uses clause.

I believe this is the closest we can get to lambda expressions in Delphi.