Methods
Organizing common
actions
Copyright © 2005-2017 Curt Hill
A Problem
• The simple objects are just moved
• Those which have moving parts
should move them
– The fish should move its tail back and
forth, open and close its mouth
• Doing it once is not problem
• More than once gets real tedious
• We do not want to use the move
method but the swim method should
take this into account
Copyright © 2005-2017 Curt Hill
The Solution
• A method is a group of instructions
that are bundled together
• They can be created and then
executed like any of the predefined
methods that come with the actors
• The goal is now to create a swim
method that moves the fish forward
and wags the tail as it is moving
• Better yet it is easy to do
Copyright © 2005-2017 Curt Hill
Methods
• Three steps:
• Create a new method
– Uses the button in Details Pane
• Put the new statements in the
method
• Call the method from elsewhere
Copyright © 2005-2017 Curt Hill
Creation
• Next we look at the creation in three
screens
• In the first we have turtle selected
– The mouse is over the Create New Method
Button
– Notice the hint showing
• Second we name the method
– In this case swim
• Third we now have two method tabs
– The leftmost is the first method which starts
when the world starts
– The rightmost is the new empty method
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Put New Statements in Method
•
•
•
•
•
Same procedure as before
Drag statements in
In this case one move forward
One set of turns for each foot
A Do Together and four Do In Orders
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Calling the New Method
• User-defined methods are just like
predefined methods
• Using a predefined method is just
like using one you created
• Mostly
• Observe the following screen shot of
the turtle swim
• Notice:
– New one is above the button
– It also has an edit button
– It is used in the Method Edit pane
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Differences
•
•
•
•
Slightly different on the left
Somewhat different on the right
Most methods have a parameter
A parameter modifies how the action
occurs
• The move method has two obvious
parameters
– Direction
– Distance
• A move cannot be given without
these
Copyright © 2005-2017 Curt Hill
Parameters
• A parameter is a value that is
passed to the method when it is
executed
• Some methods have no parameters
• Many methods have required
parameters and optional parameters
• A required parameter must be given
• An optional parameter may be given
otherwise there is a good default
value
Copyright © 2005-2017 Curt Hill
Parameter for swim?
• Swim does a move but does not
allow the move distance to be set
• Let us make the distance a
parameter
• This will be plugged into the move
directly
• How is this done?
– Observe the swim method
– Create New Parameter button
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Create New Parameter
• The Create New Parameter button
brings up a dialog box
• In this box we choose a type and a
name
• The name is how the parameter is
referenced inside the method
• The type is the kind of data:
– Number, boolean, object, string
• Here is a shot of this:
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Using the Parameter
• Anywhere a constant number may
be used a numeric parameter may
now be used
• When a numeric is specified in a
drop down list there are three
options besides a constant
– Other – you specify on calculator
– Expression – a parameter or variable
– Math – a calculation using parameter
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Math
• Instead of a numeric we may also
use a calculation
• This gets somewhat tedious to
specify but we can make it work
• To get an expression like:
time / 4
we need to first specify the
expression time then specify math
• Here is the second half
Copyright © 2005-2017 Curt Hill
Copyright © 2005-2017 Curt Hill
Math Revisited
• The drag and drop approach gets to
be a problem in math expressions
that are somewhat complicated
• First step is set the item that is to left
of operator
• Second step is to specify a math and
then choose the operator and the
item to right
• We will see this in next exercise
Copyright © 2005-2017 Curt Hill
One More Thought
• We typically use methods in two
ways
• Capture a common action so that we
can use it again and again
– A swim or walk method
• Use it to organize our movie
– Each scene becomes a method
– The method is only called once, but it
organizes our movie
Copyright © 2005-2017 Curt Hill
Method Exercise
• In this exercise use a method to
make any type of motion more
natural
• Call the method several times
• Use parameters
Copyright © 2005-2017 Curt Hill