Chapter 14. Other SWT Listeners
In many
of the examples so far you have seen that to respond to user events
such as button clicking, you develop code using a listener. Until
now, these listeners have been specific to the widget to which they
were attached (i.e., attaching a SelectionListener
to a button to respond to the click event). The SWT provides other
Listener classes that are useful in making our
user interfaces respond to other types of user actions. To understand
event types, you must
begin with the proposition that for every action a user can take in
your application, an event will be generated by the operating system.
This means that each time the user moves the mouse, or presses a
mouse button or a key on the keyboard, an event, or multiple events,
will occur.
Most of these events go unhandled by your application. After all, for most applications do you really need to know that the user moved the mouse from point A to point B within a window? Probably not. You need only know whether the user moved the mouse into a critical area or whether the user pressed a mouse button while pointing at a widget.
For those events which you do need to capture and take action on, you
must add a Listener to your code. A
Listener must be attached to some user interface
element—the Shell,
MenuItem, or Composite, or one
of the widgets placed in one of the container-type classes. There is
no such thing as a “free-standing”
Listener.
Earlier, you were exposed to how to add the most common listeners ...
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