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CHAPTER 11 CASE STUDY 1: A SYSTEM BROWSER
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Figure 11-6. The class diagram of the system s top-level classes The class diagram looks incomplete, because there are no relationships between any of the classes. I didn t forget the relationships: There simply are none. I designed the system so that all its top-level classes are decoupled from each other. The only classes missing from the diagram are those related to the infrastructure: the LifecycleCoordinators, the builder, and the binder, which I ll discuss shortly. The classes are all pretty simple, but the class diagram tells you almost nothing about how the system is really structured, because you can t see how the parts interact when the system is running. A more useful way to show the system is with a wiring diagram, as shown in Figure 11-7. The diagram depicts the system in the cruising state, which is the normal running state entered after system startup. There s a lot going on in the diagram, so later I ll describe important parts of it with separate use cases and partial-wiring diagrams. The shaded area enclosing the signals between NavigatorSearch and CoordinatorSearch represents a background operation. NavigatorSearch runs searches in a background thread, because you don t want the UI to freeze up while a search is in progress. The system requirements also specify that a search in progress must be interruptible using the Stop button. Using a separate thread to run the search on makes it easy to stop the search at any time, without the need to constantly poll the user interface for stop commands. CoordinatorSearch controls the threading, and there is no thread-related code anywhere in the system except in CoordinatorSearch. When the user clicks the Search button, NavigatorSearch fires a SearchRequested event to CoordinatorSearch, which spawns a background thread to run the search on. By keeping all the threading logic in the Coordinator, you can keep the NavigatorSearch Worker relatively simple.
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StatusBar Messages
OnViewIcons
Message
ViewIcons
Viewing Mode
ViewIcons ViewDetails Message
OnViewDetails ViewDetails
ViewIcons ViewDetails
W3 W2
Clear Add ItemFound OnItemFound
ShowIcons ShowIcons ShowDetails OnMessage ShowDetails OnMessage
SearchRequested OnSearchRequested
Populate
OnFolderDoubleClicked
FormMenuToolBar ContentFileList ContentSearchResults
CoordinatorSearch
OnAddressChanged
AddressChanged
OnMessage
Message
ShowAddress
SearchRequested
W4 W5
OnSearchRequested
FolderChanged
SearchRequested StartSearch ItemFound Message
StartSearch OnSearchStart ItemFound FireMessage
SelectedFolder
SelectFolder
OnStartSearch OnItemFound OnMessage
OnFolderChanged OnUpSelected ParentSelected SelectParentFolder
Background Thread NavigatorSearch
StatusBar
Message Message
ViewFolders
OnMessage Message
FormMain
ShowSearch
ShowFolders
ViewSearch
NavigatorFolders
Title
Folder/Search Selection
UserSettings
Company Author Document Date
SystemBrowser Main Wiring Diagram
ShowSearch
ShowFolders
Ted Faison MainWiringDiagram.vsd 2005-11-25
Version
Page
CHAPTER 11 CASE STUDY 1: A SYSTEM BROWSER
Figure 11-7. The wiring diagram on the main parts of the system
CHAPTER 11 CASE STUDY 1: A SYSTEM BROWSER
Although the system uses a Builder and Binder, those two classes don t appear in the wiring diagram, because they don t participate in the ordinary operation of the system. They set up the various parts, wire them together, and then step out of the picture. Since the Builder and Binder work directly with all the top-level classes in the system, they are also at the center of the system s coupling diagram, shown in Figure 11-8.
FormMain
NavigatorFolders
NavigatorSearch
StatusBar
FormMenuToolBar
Builder
FormSplash
ContentFileList
CoordinatorSearch
UserSettings
ContentSearchResults
Figure 11-8. The coupling diagram on the main parts of the system The star pattern tells you that the system coupling is ideal: One class is coupled to all the others, and the classes in the periphery are decoupled from each other. The diagram only shows the Builder at the center. The Binder is also at the center, but I omitted it to keep the diagram easier to read.
Life-Cycle Management
From the life-cycle perspective, SystemBrowser is like many systems because it has three modes of operation: startup, cruise, and shutdown. In the startup state, it displays a splash screen with a progress bar while the system is initialized. The splash screen is shown in Figure 11-9.
Figure 11-9. The splash screen displayed by SystemBrowser
CHAPTER 11 CASE STUDY 1: A SYSTEM BROWSER
During startup, the user s settings are read from a local file. In the cruise state, the main user interface is shown. The system spends most of its time in the cruise state. In the shutdown state, the UI is hidden to prevent further user interaction with the system. During shutdown, the user s settings are persisted to disk. SystemBrowser uses a dedicated LifecycleCoordinator to manage its life-cycle states. Each state has its own Coordinator, as shown in the wiring diagram in Figure 11-10.
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