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Model
• Defines and
manages the data
• Responds to the
controller requests
View
• Displays model to
the user
• Provides interface
for the controller
Controller
• Updates model in
response to events
• Updates view with
model changes
Model-View-Controller Pattern
Calls the
methods or
functions of
Division
can apply
to classes
or modules
A Standard GUI Application
Update the display
No major computation
Animates the
application,
like a movie
Check for user input
Process that user input
Update the models
Must We Write this Loop Each Time?
while program_is_running:
# Get information from mouse/keyboard
# Handled by OS/GUI libraries
# Your code goes here
# Draw stuff on the screen
# Handled by OS/GUI libraries
Must We Write this Loop Each Time?
while program_is_running:
# Get information from mouse/keyboard
# Handled by OS/GUI libraries
# Your code goes here
# Draw stuff on the screen
# Handled by OS/GUI libraries
Why do we need to
write this each time?
Would like to “plug in” code
Callback Functions
• Given : predefined code that
calls some function
§ But function not defined
§ You want to replace it with
your function
• You redefine that function
§ By overriding it in a subclass
(do this in A7)
§ Or by storing a reference to
your function somewhere
(“registering” your callback)
§ Works the same either way
while program_running:
# Get input
# Your code goes here
callback()
# Draw
See callback.py
Example: Animation
• Callback: animate(…)
§ Called 60x a second
§ Moves back and forth
• Animate is a method
§ Associated with an object
§ Object has changing state
• Examples of state
§ Ellipse position
§ Current velocity
§ Current animation step
def animate(self,dt): """Animate the ellipse back & forth""" if self._steps == 0:
Initialize
… elif self._steps > ANIMATION_STEPS/2:
Move away
x = self._ellipse.pos[0] y = self._ellipse.pos[1] self._ellipse.pos = (x+self._vx,y+self._vy) self._steps = self._steps - 1 else: # Move back x = self._ellipse.pos[0] y = self._ellipse.pos[1] self._ellipse.pos = (x-self._vx,y-self._vy) self._steps = self._steps - 1
State Across Multiple Callbacks
• Sometimes have more than
one callback function
• Example: touch events
§ on_touch_down:" User presses mouse (or a finger); does not release § on_touch_up:" Releases mouse (or finger) § on_touch_move:" Moves mouse (or finger)
• State needed to track
change in touch over time
See touch.py
Previous Touch Current Touch
State Across Multiple Callbacks
# None or previous touch
_anchor = None
def on_touch_down(self,touch):
# Track touch state
self._anchor = (touch.x,touch.y)
def on_touch_up(self,touch):
# Nothing to track
self._anchor = None
def on_touch_move(self,touch):
if not self._anchor is None:
self.drawLine(self._anchor[0], self._anchor[1],
touch.x,touch.y,LINE_COLOR)
self._anchor = (touch.x,touch.y)
See touch.py
Previous Touch Current Touch
