CHAPTER 4 Fragments ActionBar Menus

Explore how to build applications that use an ActionBar and Fragments Understand the Fragment lifecycle Learn to configure the ActionBar Implement Fragments with Responsive Design Techniques Explore animation in Fragment Transactions Experiment with Fragments, ListViews, and ArrayAdapters

4.1 Fragmentation and Android Fragments There are many shapes and screen sizes and different performance characteristics Multiple versions of Android are being used This translates into a wider audience to build applications for When designing and coding layouts, there are several factors to consider, such as spacing, positioning, size, and the grouping of user interface controls Layouts must be compatible with many physical screens

A Fragment is modeled as a subdivision of an Activity Fragment is integrated into an Activity, and needs an Activity to run The advantage of building applications that use Fragments is their ability to easily present a consistently well- designed user interface Fragments are particularly helpful in adapting a user experience across a wide range of devices.

4.2 The Fragment Lifecycle Fragments are associated with an activity and can be created, added or removed while the activity is running Similar to an Activity, a Fragment has its own lifecycle, as well as its own user interface The Fragment’s lifecycle is connected to the activity that owns it Each fragment has its own callback methods in the standard Activity lifecycle.

Callbacks used in the lifecycle of a Fragment. onCreateView() – bring a fragment to resumed state, interacting with user onInflate() – called every time fragment is inflated onActivityCreated() – called when fragment’s activity has been created and this fragment’s view hierarchy is instantianted onAttach() – called after the fragment has been attached to an activity onDestroyView() – informs the fragment that its view is being destroyed so that it can clean up any associated resources. Called after onStop() and before onDestroy() onDetach() – called when fragment is no longer attached to its activity, after on Destroy(). This is the final call before the fragment object is released to garbage collector

4.3 Action Bar The action bar provides information and displays control elements to the user. In a basic configuration, the action bar displays the application icon and a title The title often identifies the running activity Users are given an indication of where they are and a consistent identity from which to recognize the application

Action bar features: Application Icon Action Items Action overflow

4.4 ActionBar Configurations Control elements that appear directly on the action bar as an icon and/or text are known as action buttons When an Activity starts, its associated layout is inflated on the screen and the action bar is populated with action buttons The activity's onCreateOptionsMenu() method is responsible for inflating a menu hierarchy from a specified XML resource file

4.4.1 Overflow on the Action Bar Narrow devices can often require the use of the overflow button When creating layouts on devices with a narrow screen, use ifRoom to request that an item appear in the action bar Allow the system to move elements into the overflow when there is not enough room

4.4.2 Adding an Action View An action view is simply a widget that appears in the action bar as a substitute for an action button An action view provides quick access to heavily used actions Consider a collapsible search view widget. A search action view can be added as an embedded search view widget in the action bar To declare an action view, the actionLayout or actionViewClass attribute can be added to an item to specify either a layout resource or a widget class

4.5 Responsive Design with Fragments Responsive design works across different screens sizes Responsive design techniques should also be applied to Android applications for solving interactive design and layout problems Responsive design is used for heavy data driven content. Adaptive design is primarily used for the re- arrangement of fixed user interface elements in an application

Responsive design revolves around a master/detail flow interface design pattern The user is provided with a list of items Upon selecting one of the items, additional information relating to that item is then presented to the user

This design concept is called responsive in the sense that list and detail panels of the app can change based on the width of the device On a large tablet-sized Android device, the screen is large enough to display both panels The master list can appear as a narrow vertical panel along the left hand edge of the screen while the remainder of the screen can display the detail panel This arrangement is referred to as two- pane mode.

Responsive design makes use of Fragments A user interface can be divided into multiple panes using Fragments and reused in more than one screen of an application, as shown in the following figure Fragments can be combined or separated on a device When building an application that follows a similar master/detail design pattern, the application often needs a set of Java and XML layout resource files

4.6 Animation in Fragment Transactions Transition animations can be applied directly to fragments that are entering and exiting a transaction The FragmentManager provides the structure that handles transactions between fragments A transaction refers to the sequence of steps that add, replace, or remove fragments. Operations performed by the FragmentManager will occur inside a transaction

4.7 ListViews and Dynamic Data A ListView is similar to a ScrollView A ScrollView is an extension of the FrameLayout, and is suitable for holding a single control element It provides the user with the scroll mechanism to reveal more content than can be displayed on the screen at once A LinearLayout, containing multiple View items, can be placed within a ScrollView

A ListView is a specialized control that is optimized for displaying long lists of items When the data content for the layout is dynamic or not pre-determined, it is possible to use a layout that subclasses an AdapterView to populate the layout with views at runtime

4.8 Handling Click Events in a ListView A ListView might be populated with items that need to respond to a click event You can respond to click events on an item in an AdapterView by implementing the AdapterView.OnItemClickListener interface The onItemClick () callback method will always be invoked when an item in the AdapterView has been clicked.