android-Planning for Multiple Touchscreen Sizes,Providing Descendant and Lateral Navigation

> Planning for Multiple Touchscreen Sizes

 The exhaustive screen map from the previous lesson isn't tied to a particular device form factor, although it can generally look and work okay on a handset or similar-size device. But Android applications need to adapt to a number of different types of devices, from 3" handsets to 10" tablets to 42" TVs. 

   Note: Designing applications for television sets also requires attention to other factors, including interaction methods (i.e., the lack of a touch screen), legibility of text at large reading distances, and more.

 3 to 4-inch screens are generally only suitable for showing a single vertical pane of content at a time, be it a list of items, or detail information about an item, etc. Thus on such devices, screens generally map one-to-one with levels in the information hierarchy (categories → object list → object detail).

 Users are especially accustomed to multiple panes on larger screens from years and years of desktop application and desktop web site use. Many desktop applications and websites offer a left-hand navigation pane or use a master/detail two-pane layout.

Implementation Note: After deciding on the screen size at which to draw the line between single-pane and multi-pane layouts, you can provide different layouts containing one or multiple panes for devices in varying screen size buckets (such as large/xlarge) or varying minimum screen widths (such as sw600dp).

Implementation Note: While a single screen is implemented as an Activity subclass, individual content panes can be implemented as Fragment subclasses. This maximizes code re-use across different form factors and across screens that share content.

 Although we haven't begun arranging user interface elements on our screens yet, this is a good time to consider how your multi-pane screens will adapt to different device orientations. Multi-pane layouts in landscape work quite well because of the large amount of available horizontal space. However, in the portrait orientation, your horizontal space is more limited, so you may need to design a separate layout for this orientation.

> Providing Descendant and Lateral Navigation

 One way of providing access to the full range of an application's screens is to expose hierarchical navigation.

 There are two types of sibling screens: collection-related and section-related screens. Collection-related screens represent individual items in the collection represented by the parent. Section-related screens represent different sections of information about the parent.   

 There are some obvious immediate benefits of tabs over simpler list- and button-based navigation:

• Since there is a single, initially-selected tab, users have immediate access to that tab's content from the parent screen.
• Users can navigate quickly between related screens, without needing to first revisit the parent.

 Note: when switching tabs, it is important to maintain this tab-switching immediacy; do not block access to tab indicators by showing modal dialogs while loading content.

 For collection-related screens, horizontal paging is most intuitive when there is a natural ordered relationship between screens, for example if each page represents consecutive calendar days. For infinite collections (again, calendar days), especially those with content in both directions, this paging mechanism can work quite well.