03A Fragments and MVC

Question 1

Fragments

Answer 1

• A fragment is an independent module with its own user interface
• You can create a fragment without a UI to
handle background tasks, but this is not the usual case
• Fragments exist only when embedded within an Activity

Question 2

Creating Fragments

Answer 2

• Within Android Studio you can right-click on the “app” root, select New, and select
Fragment
• You’ll be presented with three choices:
– Fragment (blank)
– Fragment (list)
– Fragment (with a +1 button)
• Your fragment will have a layout defined in the XML
• The code for your fragment will be an inner class within the main class
• Your fragment extends the Fragment class
• If you have a UI, override the
onCreateView method to inflate it

Question 3

The Fragment Lifecycle

Answer 3

Fragment.onAttach->Fragment.onCreate-> Fragment.onCreateView-> Fragment.onActivityCreated (Visible) Fragment.onStart-> (Active)
Fragment.onResume->Fragment->onPause-> Fragment->onPause-> Fragment.onDestroyView-> Fragment-> onDestroy->Fragment->onDetach

Question 4

Fragments and Activities

Answer 4

• You can get a reference to the activity in
which the fragment exists:
MainActivity main = (MainActivity)getActivity();

Question 5

Compound Controls

Answer 5

• Compound controls are self-contained View Groups that contain multiple child views
• These can be treated as a single control

Question 6

Model-View-Controller (intro)

Answer 6

• This paradigm is used for many controls, but in particular, you’ll need it for lists
• The Model is the actual data
• The View is how the data are displayed
• The Controller gets input

Question 7

MVC (JList)

Answer 7

• JList does not have an “add” method
• Therefore, to add something to the list on the screen, you must add it to the model
• The View implements ActionListener to get events from the model when the data changes
• Views can show the data in different ways, depending upon the renderer

Question 8

JSpinner Models

Answer 8

• The JSpinner control has several models:
• SpinnerDateModel to cycle through dates • SpinnerNumberModel for numbers (default)
• SpinnerListModel cycles through the items in a list

Question 9

The JList Control Revisited

Answer 9

• The appearance of JList is controlled by the
Cell Renderer
• These implement the ListCellRenderer
interface, which defines the
getListCellRendererComponent method
• Thus the appropriate Cell Renderer can
display anything in a list
• ListCellRenderer subclasses should handle the cases where the cell is selected and where it is not, and whether it has the focus
• These attributes are passed as parameters to the getListCellRenderer method