Problem: commands with state and undo support How do applications - PowerPoint PPT Presentation

Problem: commands with state and undo support ● How do applications with “undo” options (e.g., formatting in word processors) support the undo? ● How can a command, e.g., load files, find line numbers, be encapsulated into a class/object? ● How can commands be combined into macro-commands or command-sequences (e.g., load files, find occurrences of str)? ➤ use the Command pattern: an abstract class with a receiver that knows how to execute the command and, when necessary, has state to support undo operations ReadCommand rc(myController); rc.execute(); ➤ macro command’s execute iterates over all commands in Vector<Command *> myCommands; ➤ This is a command that contains commands: Composite 13. 1 Duke CPS 108

Lots of command classes, what to do? ● Store command classes in a subdirectory (for the project), then use #include “commands/readcommand.h” ● Use templated commands when possible to factor out common, simple commands, e.g., that invoke certain member functions ● In small programs, using the Command pattern may not make sense, but it will pay off in larger programs and when porting code to a new language or environment ➤ often pattern payoff is not immediately apparent, but the rewards wil com 13. 2 Duke CPS 108

What about libraries? ● for both static and dynamic/shared libraries you need to specify where the library is located and what library is used ➤ -L , link/load option, takes directory as “argument” ➤ -L. -L/afs/acpub/users/o/l/ola/cps108/lib ➤ also specify -lscandir , -ltapestry , these refer to either libscandir.a or libscandir.so (similarly libtapestry.*) ➤ on Solaris, shared libraries linked by default if they exist, can override with -static option ➤ what about libiberty.a? ● You can supply both .a and .so libraries, let the user have an option. Header files must be supplied as well, typically these are in path/lib and path/include directories. 13. 3 Duke CPS 108

Some Qt info ● All slot/signal and otherwise Q-able classes must include a macro Q_OBJECT at the top of the class declaration, before public: ➤ macro/preprocessor flag is changed by CPP, the C-pre- processor (e.g., #define) ➤ any foo.h file with Q_OBJECT needs to be run through MOC to generate a MOCfoo.cc file (or fooMOC.cc ), this is in addition to the normal foo.cc file ➤ the mocdepend.perl script automatically generates the MOCfoo.cc files by grepping for Q_OBJECT ● If you have trouble, remove all .o files, especially MOC*.o files and recompile ● examples in ~ola/cps108/qtlink/examples on acpub 13. 4 Duke CPS 108