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

Duke CPS 108

• 13. 1

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

Duke CPS 108

• 13. 2

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

Duke CPS 108

• 13. 3

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
• ption. Header files must be supplied as well, typically these

are in path/lib and path/include directories.

Duke CPS 108

• 13. 4

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