Presentation on theme: "Parameters and World-level methods Alice. Our Dragon world The dragon must to take off and fly, to carry the princess."— Presentation transcript:
Parameters and World-level methods Alice
Our Dragon world The dragon must to take off and fly, to carry the princess
Storyboards We can make the dragon takeOff and fly. Dragon.takeOff Do together dragon move up 1 meter dragon flap its wings Dragon.fly Do together dragon move forward 1 meter dragon flap its wings Note that we would need very similar methods to get the dragon to land (by flying down) or to fly in other directions
A Better Solution Multiple versions of very similar code seems a bit tedious. The only things that change is the direction the dragon is to fly. A better solution is to write a more flexible method.
Parameters Built-in methods provide flexibility by providing parameters such as distance and direction. Parameters allow you to pass in values (arguments). Example Parameters: direction, distance, duration Arguments: left, 0.05 revolutions, 0.5 seconds
Kinds of Parameters Alice provides several kinds of parameters that can be used in your own methods.
The storyboard Dragon.flyInAnyDirection Parameter: whichDirection Do together dragon move in whichDirection dragon flap its wings In this example, we can write just one method and use a parameter to specify: which direction the dragon is to fly.
Demo Concepts illustrated Enter name and select the type of each parameter whichDirection is a Direction parameter A parameter acts as a placeholder in the instruction Arguments are passed to the parameter in the call to the method
A Number parameter Add a Number parameter to specify the distance the dragon travels as it is flying. Note that the call to the method must now include an argument for the distance.
World-level methods It is also possible to create world-level methods These are used when there are references to multiple objects in the world
Example Consider our dragon world The dragon has taken off Now it must fly to the princess. Such a method will involve 2 objects: the dragon and the princess
Demo: Starting a new method First, to associate the new method with the World select the World tile in the Object Tree select the methods tab in the details area click on the "create new method" button