1. Organizing common actions
Methods
Organizing common actions
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2. 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
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3. 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
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4. 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
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5. 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
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9. 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
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11. 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
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13. 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
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14. 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
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15. 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
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17. 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:
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19. 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
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21. 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
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23. 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
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24. 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
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25. Method Exercise
In this exercise use a method to make any type of motion more natural
Call the method several times
Use parameters
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