Basic GUI programming

Components in Android

• View - simple GUI elements

• ViewGroup - a group of Views which can contain other ViewGroups

How can you create a component?

Programmatically

XML

<TextView 
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

new TextView(
    new LayoutParams(MATCH_PARENT, 
                     MATCH_PARENT))

Components attributes

Important

• layout_width - required
• layout_height - required
• layout_<something> - defines layout properties
• ID - referenced as int
  • @ - to expand the rest of the string and identify it as a resource
  • + means that it is a new resource and must be created
  • android has built-in ids- 

    @android:id/empty

• gravity vs. layout_gravity - inside vs. outside

Layout Params (layout_<something>)

wrap_content vs match_parent

What is a View?

A view has a location (top and left coordinates) and dimensions (width and height).

View Dimensions

• dp - Density-independent Pixels - An abstract unit that is based on the physical density of the screen.
• sp - Scale-independent Pixels - This is like the dp unit, but it is also scaled by the user's font size preference.
• pt
• px
• mm
• in

Containers

LinearLayout

RelativeLayout

WebView

FrameLayout

Linear vs Relative

+ layout_weight

+ vertical/horizontal

+ faster performance

- low flexibility

+ great flexibility

+ overlay with ease

+ support for different screens

- lots of ids declaration

- slow performance

Input controls

Buttons

EditText

Checkboxes

Toggle

Radio

Spinner

Pickers

Something more about controls

• inputType - phone
  • bitwise operations
• imeOptions - actions to be done
• imeLabel
• hint
• AutoCompleteTextView

EditText

ToggleButton

• onCheckedChangeListener
• onToggleListener

Toast - another way for debugging

new Toast(context, "Test", Toast.LENGHT_SHORT)
.show()

Let's code!

ListViews & Adapters

What is a ListView?

• Sublclass of AdapterView - populate the layout with views at runtime.

• Needs an Adapter to populate the components

• The adapter is a middleman between the data source and the AdapterView layout - it adapts the data and creates each listview entry

ArrayAdapter

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, myStringArray);

• Context
• XML layout for a single row
• List of data

To create an adapter you need:

Let's try it!

Custom Adapters

• extend BaseAdapter - SOURCE
• override getView
• override getItem
• override getCount
• override getItemId

Reusing views to get a custom look

Let's try it!

GridView

Just replace ListView with GridView

• Determine columns count
• Determine cell size
• More scalable than ListView
• Cells better than rows
• Takes more screen space

Let's try it!