Mastering Delphi Programming: A Complete Reference Guide

Command-based editor

A command pattern has many moving parts, so it is not a surprise that the example for this pattern is one of the more complicated ones in this book.

The Editor project in the Command folder implements a very simple text editor that internally uses the command pattern. Although it offers only primitive editing capabilities, the example implements both an undo system and a simple macro recorder.

The client part of the pattern is represented by the TfrmCommand form in the EditorMain unit. The command receiver is a TMemo field, which is for reasons of simplicity part of the main form. As we'll see later, the code actually implements two editors, each with its own memo component as a receiver.

The command hierarchy starts ...