Free pascal tstrings.addstrings11/28/2022 Procedure TForm1.ButtonAddClick(Sender: TObject) begin Procedure TForm1.FormCreate(Sender: TObject) beginĪ button of the form adds a random date to the list (of course, I've included in the project the unit containing the date component built in the previous chapter): This list object is created when the form itself is created: Its form has a private variable, holding a list of dates: It also shows the pitfalls of this approach. The ListDemo example demonstrates just this. When you need a list of any kind of data, you can generally declare a TList object, fill it with the data, and then access the data while casting it to the proper type. We can write an example focusing on the use of the generic TList class. ShowMessage ('String found') finally sl.Free end end Using Lists of Objects #FREE PASCAL TSTRINGS.ADDSTRINGS CODE#To fill a string list with items and later check whether one is present, you can write code like this: var sl: TStringList idx: Integer īegin sl := TStringList.Create try sl.Add ('one') sl.Add ('two') sl.Add ('three') // later idx := sl.IndexOf ('two') if idx >= 0 then In Delphi 6, the TList class has an Assign method that, besides copying the source data, can perform set operations on the two lists, including and, or, and xor. There is a Count property, as well as typical access methods, such as Add, Insert, Delete, Remove, and search methods (for example, IndexOf). You can operate on lists using the array notation (" ") both to read and to change elements. All these lists have a number of methods and properties. To loop through a list, you can use a simple for statement based on its index, as if the list were an array. The two classes of lists of strings also have ready-to-use methods to store or load their contents to or from a text file, SaveToFile and LoadFromFile. For example, you can use them for dictionaries of associated objects or to store bitmaps or other elements to be used in a list box. This opens up a number of different uses for these classes. TStringList and TStrings objects have both a list of strings and a list of objects associated with the strings. You can use this class to define a list of strings in a program. TStringList, a subclass of TStrings, defines a list of strings with their own storage.For this reason, TStrings objects are used only as properties of components capable of storing the strings themselves, such as a list box. This class defines an abstract list of strings. TStrings is an abstract class to represent all forms of string lists, regardless of their storage implementations.The advantage of dynamic arrays over a TList, instead, is that dynamic arrays allow you to indicate a specific type for contained objects and perform the proper compile-time type checking. A TList is more flexible than a dynamic array, because it is expanded automatically, simply by adding new items to it. TList defines a list of pointers, which can be used to store objects of any class.Mastering Delphi Lists are represented by the generic list of objects, TList, and by the two lists of strings, TStrings and TStringList:
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