Extended Example: Steering the Car Using a Mouse | 193Note that the new interface turns the car in discrete steps (50 degrees on each key
press). Therefore, to make a hard turn right, the right arrow key should be pressed
and held down (to generate multiple key down events). A quick press and release of
the appropriate keys results in small turns.
Extended Example: Steering the Car Using a Mouse
If the target interface is designed with flexibility and future use in mind, the adapter
can be used in multiple contexts. Because steering is accomplished in discrete steps
using theturnMoreToTheLeft( ),turnMoreToTheRight( ), andgoStraight( )methods
implemented in the adapter, it can be used with different input devices such as a joy-
stick or mouse. Let’s look at how a client can use mouse input to steer the car. For
example, we can use a mouse click to straighten the steering and make the car go
straight. How can a left and right turn be accomplished using the mouse? One way is
by keeping track of the horizontal movement of the mouse as shown in Figure 5-6. If
the mouse moves to the left, we can callturnMoreToTheLeft( ). If the mouse moves to
the right, we can callturnMoreToTheRight( ).
The basic client is similar to theMainclass (Example 5-12) that used keyboard input
to steer the car. The following changes need to be made to theMainclass in order to
steer the car using the mouse. We need to add a new property to keep track of the
previous horizontal location of the mouse on the stage, to figure out if the mouse
moved to the left or right. The initial horizontal location will be zero.
private var oldMouseStageX:Number = 0;An additional change is to attach different listener functions that respond to mouse
events rather than keyboard events. Instead of attaching a listener function to
Figure 5-6. The interface showing mouse input
Ignition keyfunction start() :voidfunction goStraight() :void
Mouse moves to
the left
function turnMoreToTheRight() :voidfunction turnMoreToTheLeft() :voidMouse clickMouse moves to
the right