Event-driven Design

An Event to Remember - A Two Act Play about Events

Act 1: On the Golf Course

Main Program

Role:

Get the system started

Responsibilities:

Main
```
  Initialize.
  Run taskmaster.
```

Type Mouse

Role:

Record student input from mouse. This can happen at any time.

Responsibilities:

RecordInput

  Record x,y position and type of event in mouseEvent.
  Put mouseEvent on EventQueue.

Type Taskmaster

Role:

Process events and schedule tasks

Responsibilities:

Run

  Repeat Forever
    Call ProcessEvent for GUI.
    Execute next task.

Type GUI

Role:

Display graphics on screen and arbitrate events

Responsibilities:

ProcessEvent

  Get next event from eventQueue and call it anEvent.
  Determine which widget was clicked on.
  If widget is a pushbutton and 
    a buttonPress is followed by a buttonRelease then
    Put task "activate anEvent" for widget on task Queue.
  else
    Put task (event_name _ " anEvent") for widget on taskQueue.

Type Pushbutton

Role:

Handle activate events when clicked on

Responsibilities:

activate anEvent

  Find the manager of the dialogbox which owns me.
  Send "activate anEvent" to manager.

Type Golfman

Role:

Process activities associated with golfing

Responsibilities:

activate anEvent

    Run my "eraseActivate" method (if it exists).

eraseActivate
```
erase the window associated with me.
```

Type Window

Role:

Display graphics and receive input events (button and key)

Responsibilities:

buttonPress anEvent

  Find the manager of the dialogbox which owns me.
  Send "buttonPress anEvent" to manager.

erase Erase the window.

Act 2: In the Club House

Type Figure

Role:

Process activities for shape/behavior objects

Responsibilities:

buttonPress anEvent

  Send "buttonPress anEvent" to its form.
  Send "buttonPress anEvent" to its action.

Type Click

Role:

Process a buttonClick by executing the associated method.

Responsibilities:

buttonPress anEvent
```
  Note time of buttonPress.
```

buttonRelease anEvent

  If time is < 300 ms then
    execute double-click method.
  else
    execute single-click method.

Type Manualman

Role:

Responsibilities:

buttonPress anEvent

  Find the figure containing coordinates of anEvent.
  Send "buttonPress anEvent" to the figure.