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Android Layouts

Android Layouts. Layouts. Define the user interface for an activity Layouts are defined in .xml files within /res/layout folder different layout can be designed for lanscape view placed within /res/layout-land folder Handful of layouts to choose from

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Android Layouts

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  1. Android Layouts

  2. Layouts • Define the user interface for an activity • Layouts are defined in .xml files • within /res/layout folder • different layout can be designed for lanscape view • placed within /res/layout-land folder • Handful of layouts to choose from • All derived from the class:android.view.ViewGroup

  3. View class • Any widget or ViewGroup placed as part of interface on an Activity is a View • 11 direct subclasses • 62 indirect subclasses • LinearLayout • TableLayout • EditText • Button • Others http://developer.android.com/reference/android/view/View.html

  4. View attributes • Apply to any instance of a View • syntax: android:layout_attribute_name=“value” • layout_height and layout_width • values: match_parent or wrap_content • fill_parent deprecated (renamed to match_parent as of 2.2) • layout_margin • extra space on all sides of item • layout_marginX (i.e. X= Top, Bottom, Right, Left) • layout_gravity • gravity • text (for labels, buttons, etc.)

  5. Sizing options • preferred units • dp or dip – device independent pixels • scales size according to screen density • 1 dp is equivalent to 1 pixel on 160 dpi screen • sp – scale-independent pixels • scales fonts according to user’s font size • other options • px • actual pixels • mm and in – millimeters and inches • pt – points (1/72”)

  6. Layouts • Available layouts • AbsoluteLayout • Deprecated as of 1.5 - allowed specific x, y coordinates • Common Layouts • LinearLayout • Default • Allows child items to be placed in a single row or column • TableLayout • Allows child items to be placed in multiple rows and columns • More sophisticated/specialized layouts • RelativeLayout • Allows child items to be placed relative to each other • FrameLayout • Allows child items to be stacked on one another

  7. LinearLayout • Child items placed in single row or column • Important attributes for LinearLayout • orientation • applies to parent • “vertical” = single column • “horizontal” = single row • layout_width and layout_height • decide if the layout should take up: • the entire width (height) of the screen • minimum width (height) needed • specific width (height) desired

  8. Sample .xml file <?xml version="1.0" encoding="utf-8"?> <LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width=“match_parent“ android:layout_height=“match_parent“ > <TextView android:layout_width=“match_parent" android:layout_height="wrap_content“ android:layout_margin="2dp“ android:text="View me" /> <Button android:layout_width=“match_parent" android:layout_height="wrap_content" android:layout_margin=“2dp" android:text="Push me" /> </LinearLayout>

  9. TableLayout • Places items in rows and columns • Important attributes • collapseColumns (hides columns) • =“*”, =“1”, =“0,3”, etc. • stretchColumns (displays columns) • layout_span • allows child to span multiple columns

  10. Sample .xml file <?xml version="1.0" encoding="utf-8"?> <TableLayoutxmlns:android=“http://schemas.android.com/apk/res/android” android:layout_width=“match_parent“ android:layout_height=“match_parent" android:stretchColumns=“*" > <TableRow> <Button android:text="Cell 1,1“/> <Button android:text="Cell 1,2”/> </TableRow> <TableRow> <Button android:text="Cell 2,1”/> <Button android:text="Cell 2,2”/> </TableRow> </TableLayout>

  11. RelativeLayout • Currently the default layout supplied in Eclipse • Tends to work the best with the visual editor • Where child items are in relation to: • parent • each other • Sometimes allows for one layout to be used instead of layouts within layouts • Many attributes • See documentation on RelativeLayout.LayoutParams class

  12. RelativeLayout • Important attributes • layout_X where X is: • centerInParent • centerHorizontal (or Vertical) • alignParentTop (or Bottom or Left or Right) • alignRight (or Left or Top or Bottom) • (=“@+id/childIdName”) • aligns specified edge of each child • often causes overlap • above (or below or toLeftOf or toRightOf) • (=“@+id/childIdName”) • aligns children relatively to each other accordingly

  13. Sample .xml file <?xml version="1.0" encoding="utf-8"?> <RelativeLayoutxmlns:android=“http://schemas.android.com/apk/res/android” android:layout_width=“match_parent“ android:layout_height="match_parent“ > <TextView android:id="@+id/tv1“ android:layout_width="wrap_content" android:layout_height="wrap_content“ android:layout_centerInParent="true“ android:text="View me“ /> <Button android:layout_width="wrap_content“ android:layout_height="wrap_content" android:layout_centerInParent="true" android:layout_toRightOf="@+id/tv1" android:text="Push me" /> </RelativeLayout>

  14. FrameLayout • Places items on top of each other <?xml version="1.0" encoding="utf-8"?> <FrameLayoutxmlns:android=“http://schemas.android.com/apk/res/android” android:layout_width="match_parent“ android:layout_height="match_parent“ > <TextView android:layout_width="wrap_content“ android:layout_height="wrap_content“ android:text="This is big text!“ android:textSize="20pt“ /> <TextView android:layout_width="wrap_content“ android:layout_height="wrap_content“ android:text="I am small...“ android:textSize="8pt" /> </FrameLayout>

  15. Layout Orientations • Portrait • Default view • Landscape • When device is rotated 90° • To set specific layouts for each • \res\layout\main.xml for portrait layout • layout folder is provided • \res\layout-land\main.xml for landscape layout • layout-land folder must be created • file name and variable names within file must match • not restricted to main.xml

  16. Layout Orientations • Orientation can be locked • screenOrientation attribute of Activity • android:screenOrientation="portrait" • Each Activity handled separately • can do any combination of locked and unlocked Activities • can lock all, but must do each individually

  17. Common Views • User-interface views placed within layouts • TextView • EditText • Button • CheckBox • RadioButton • Spinner • Many others

  18. Determining a given View’s .xml attributes • Use Android reference to find class • Example: Button • View XML attributes of the class • Button does not have any listed • View XML attributes of the Ancestor classes • In this case, TextView and View • Use eclipse pop-up help in .xml file

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