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Parameters and World-level methods

Alice. Parameters and World-level methods. 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

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Parameters and World-level methods

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  1. Alice Parameters and World-level methods

  2. Our Dragon world • The dragon must to take off and fly, to carry the princess

  3. 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

  4. 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.

  5. 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

  6. Kinds of Parameters • Alice provides several kinds of parameters that can be used in your own methods.

  7. The storyboard Dragon.flyInAnyDirection Parameter: whichDirection Do together dragon move in whichDirection dragonflap its wings • In this example, we can write just one method and • use a parameter to specify: • which direction the dragon is to fly.

  8. 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

  9. 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.

  10. 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

  11. 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

  12. 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

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