PowerPoint Template

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Programming with Android Introduction
Programming with Android Layouts
Luca Bedogni Marco
Di Felice Dipartimento di
Scienze dellInformazione
Università di Bologna
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Views outline

• Main difference between a Drawable and a View is
  reaction to events
• Could be declared in an XML file
• Could also be declared inside an Activity
• Every view has a unique ID
• Use findViewById(int id) to get it
• Views can be customized

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Some useful methods

• getLeft()
• getTop()
• getMeasuredWidth()
• getMeasuredHeight()
• getWidth()
• getHeight()
• requestLayout()
• invalidate()

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ViewGroup and layout

• ViewGroup is a view container
• It is responsible for placing other views on the
  display
• Every layout must extend a ViewGroup
• Every view needs to specify
• androidlayout_height
• androidlayout_width
• A dimension or one of match_parent or
  wrap_content

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Layouts

• Some layouts are pre-defined by Android
• Some of these are
• LinearLayout
• RelativeLayout
• TableLayout
• FrameLayout
• AbsoluteLayout
• A layout could be declared inside another layout

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LinearLayout

• Dispose views on a single row or column,
  depending on androidlayout_orientation
• The orientation could also be declared via
  setOrientation(int orientation)
• orientation is one of HORIZONTAL or VERTICAL
• Has two other attributes
• gravity
• weight

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LinearLayout
lt?xml version"1.0" encoding"utf-8"?gt ltLinearLayo
ut xmlnsandroid"http//schemas.android.com/apk/r
es/android" androidlayout_width"fill_parent"
androidlayout_height"fill_parent"
androidorientation"vertical" gt lt!-- Also
horizontal --gt ltButton
androidid"_at_id/button1"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString1" /gt
ltButton androidid"_at_id/button2"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString2"
/gt lt/LinearLayoutgt
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LinearLayout
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LinearLayout
lt?xml version"1.0" encoding"utf-8"?gt ltLinearLayo
ut xmlnsandroid"http//schemas.android.com/apk/r
es/android" androidlayout_width"fill_parent"
androidlayout_height"fill_parent"
androidorientation"vertical" gt ltButton
androidid"_at_id/button1"
androidlayout_width"match_parent"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString1" /gt
ltButton androidid"_at_id/button2"
androidlayout_width"wrap_content"
androidlayout_height"match_parent"
androidtext"_at_string/buttonString2"
/gt lt/LinearLayoutgt
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LinearLayout
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LinearLayout weight
lt?xml version"1.0" encoding"utf-8"?gt ltLinearLayo
ut xmlnsandroid"http//schemas.android.com/apk/r
es/android" androidlayout_width"fill_parent"
androidlayout_height"fill_parent"
androidorientation"horizontal" gt ltButton
androidid"_at_id/button1"
androidlayout_width"match_parent"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString1"
androidlayout_weight"1" /gt ltButton
androidid"_at_id/button2"
androidlayout_width"match_parent"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString2"
androidlayout_weight"2"
/gt lt/LinearLayoutgt
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LinearLayout weight
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LinearLayout gravity
lt?xml version"1.0" encoding"utf-8"?gt ltLinearLayo
ut xmlnsandroid"http//schemas.android.com/apk/r
es/android" androidlayout_width"fill_parent"
androidlayout_height"fill_parent"
androidorientation"horizontal" gt ltButton
androidid"_at_id/button1"
androidlayout_width"match_parent"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString1"
androidlayout_weight"1" /gt ltButton
androidid"_at_id/button2"
androidlayout_width"match_parent"
androidlayout_height"wrap_content"
androidtext"_at_string/buttonString2"
androidlayout_weight"2"
androidlayout_gravity"center_vertical"
androidgravity"topcenter" /gt
lt/LinearLayoutgt
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LinearLayout gravity
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LinearLayout problem
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RelativeLayout

• Disposes views according to the container or
  according to other views
• The gravity attribute indicates what views are
  more important to define the layout
• Useful to align views

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RelativeLayout
lt?xml version"1.0" encoding"utf-8"?gt ltRelativeLa
yout xmlnsandroid"http//schemas.android.com/apk
/res/android" androidlayout_width"match_pare
nt" androidlayout_height"match_parent" gt
ltEditText androidid"_at_id/username"
androidtext"username"
androidinputType"text"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidlayout_alignParentRight"true"
androidlayout_toRightOf"_at_id/usernameLabel" gt
lt/EditTextgt ltTextView
androidid"_at_id/usernameLabel"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidlayout_alignBaseline"_at_id/username"
androidtext"Username" /gt
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RelativeLayout
ltEditText androidid"_at_id/password"
androidtext"password"
androidinputType"textPassword"
androidlayout_below"_at_id/username"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidlayout_alignLeft"_at_id/username"
androidlayout_alignParentRight"true"
androidlayout_toRightOf"_at_id/usernameLabel" gt
lt/EditTextgt ltTextView
androidid"_at_id/passwordLabel"
androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidlayout_alignBaseline"_at_id/password"
androidtext"Password" /gt lt/RelativeLayoutgt
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RelativeLayout
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TableLayout

• As the name say, similar to a Table
• Has some attributes to customize the layout
• androidlayout_column
• androidlayout_span
• androidstretchColumns
• androidshrinkColumns
• androidcollapseColumns
• Each row is inside a ltTableRowgt element

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TableLayout
lt?xml version"1.0" encoding"utf-8"?gt ltTableLayou
t androidlayout_width"fill_parent" androidlayo
ut_height"fill_parent" xmlnsandroid"http//sche
mas.android.com/apk/res/android" androidid"_at_id/
tableLayout"gt ltTableRow androidlayout_width
"wrap_content" androidlayout_height"wrap_content
androidid"_at_id/firstRow"gt
ltButton androidid"_at_id/button1 androidlayo
ut_width"wrap_content androidlayout_height"
wrap_content androidtext"Button" /gt
ltButton androidid"_at_id/button2
androidlayout_width"match_parent"
androidlayout_height"match_parent"
androidtext"Button" /gt ltButton
androidid"_at_id/button3"
androidlayout_width"match_parent"
androidlayout_height"match_parent"
androidtext"Button" /gt lt/TableRowgt
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TableLayout
ltTableRow androidlayout_width"wrap_con
tent" androidlayout_height"wrap_conten
t" androidid"_at_id/secondRow"gt
ltButton androidlayout_column"1" android
layout_span"2" androidid"_at_id/button4
" androidlayout_width"wrap_content"
androidlayout_height"wrap_content"
androidtext"Button"gt
lt/Buttongt lt/TableRowgt lt/TableLayoutgt
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TableLayout
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FrameLayout and AbsoluteLayout

• FrameLayout
• Adds an attribute, androidvisibility
• Makes the user able to define layouts managing
  the visibility of views
• AbsoluteLayout
• Deprecated
• Specify position with x and y
• Pay attention to different resolutions

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Adapters

• Used to visualize data
• Make a ViewGroup to interact with data
• Some methods
• isEmpty()
• getItem(int position)
• getCount()
• getView()

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AdapterView

• A ViewGroup subclass
• Its subchilds are determined by an Adapter
• Some subclasses
• ListView
• GridView
• Spinner
• Gallery

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ListView example
public class HelloAndroidActivity extends
Activity _at_Override public void
onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState)
setContentView(R.layout.list) String
data "First", "Second", "Third"
ListView lv (ListView)findViewById(R.id.list)
lv.setAdapter(new
ArrayAdapterltStringgt(this, android.R.layout.simple
_list_item_1, data)) lt?xml
version"1.0" encoding"utf-8"?gt ltListView
xmlnsandroid"http//schemas.android.com/apk/res/
android" androidlayout_width"match_parent"
androidlayout_height"match_parent"
androidorientation"vertical"
androidid"_at_id/list" /gt
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ListView
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Other views/adapters

• Spinner, selection of multiple items
• Gallery, images
• ExpandableListView, list with hidden values
• TabWidget, tabbed layouts

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