Android layouts

© 2012 Marty Hall
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Layouts:
Organizing the Screen
Originals of Slides and Source Code for Examples:
http://www.coreservlets.com/android-tutorial/
© 2012 Marty Hall
For live Android training, please see courses
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Topics in This Section
• LinearLayout
• Strategy of nesting layouts
• Using color files
– And preview of Localization
• Layout weights
• RelativeLayout
• TableLayout
• hierarchyviewer
5
© 2012 Marty Hall
Overview

Main Layout Strategies
• XML-based
– Declare layout in res/layouts/some_layout.xml
• Set various XML properties
• Use visual editor in Eclipse
– Load with setContentView(R.layout.some_layout)
• Java-based
– Instantiate layout, set properties, insert sub-layouts
• LinearLayout window = new LinearLayout(this);
• window.setVariousAttributes(…);
• window.addView(widgetOrLayout);
– Load with setContentView(window)
• This tutorial
– Uses XML-based approach. However, attributes can be
adapted for Java-based approach.7
XML Layout Attributes
• Idea
– Each Layout class has an inner class called LayoutParams that
defines general XML parameters that layout uses. These
parameters are always named android:layout_blah, and
usually have to do with sizes and margins.
– Layout classes define more specific attributes. Many inherited
from LinearLayout (which extends ViewGroup and View).
• Not named beginning with “layout_”
• Example
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:background="@color/color_1">…<LinearLayout>
8

Commonly Used Attributes
• Size
– android:layout_height, android:layout_width
• match_parent: fill the parent space (minus padding)
– Renamed from fill_parent in older versions
• wrap_content: use natural size (plus padding)
• An explicit size with a number and a dimension. See margins on next slide.
– android:layout_weight
• A number that gives proportional sizes. See example.
• Alignment
– android:layout_gravity
• How the View is aligned within containing View.
– android:gravity
• How the text or components inside the View are aligned.
– Possible values
• top, bottom, left, right, center_vertical, center_horizontal, center (i.e., center
both ways), fill_vertical, fill_horizontal, fill (i.e., fill both directions),
clip_vertical, clip_horizontal
9
(Continued)
• Margins (blank space outside)
– android:layout_marginBottom,
android:layout_marginTop, android:layout_marginLeft,
android:layout_marginRight
– Units (e.g., "14.5dp") – negative values are legal
• dp: density-independent pixels (scaled by device resol.)
• sp: scaled pixels (scaled based on preferred font size)
• px: pixels
• in: inches
• mm: millimeters
• Padding (blank space inside)
– android:paddingBottom, android:paddingTop,
android:paddingLeft, android:paddingRight
• Values are numbers with units as above10

(Continued)
• ID
– android:id
• Used if the Java code needs a reference to View
• Used in RelativeLayout so XML can refer to earlier ids
• Colors
– android:background (color or image, for any Layout)
– android:textColor (e.g., for TextView or Button)
– Common color value formats
• "#rrggbb", "#aarrggbb", "@color/color_name"
• Click handler
– android:onClick
• Should be a public method in main Activity that takes a
View (the thing clicked) as argument and returns void
11
© 2012 Marty Hall
LinearLayout Basics

LinearLayout
• Idea
– Put components in a single row or single column
– By nesting, can have rows within columns, etc.
• Most important XML attributes
– android:orientation
• "horizontal" (a row) or "vertical" (a column)
• horizontal is the default, so can be omitted for rows
– android:gravity
• How the Views inside are aligned.
• Possible values
– top, bottom, left, right, center_vertical, center_horizontal, center
(i.e., center both ways), fill_vertical, fill_horizontal, fill (i.e., fill both
directions), clip_vertical, clip_horizontal
13
Example Summary
(Highly Nested Layouts)
• General Approach
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android=
"http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_height="match_parent">

</LinearLayout>
14

Example Details
15
Horizontal LinearLayout with gravity of center_horizontal.
<LinearLayout
android:background="@color/color_1">
<Button android:text="These"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
<Button android:text="Buttons"
<Button android:text="Are"
<Button android:text="Centered"
</LinearLayout>
Horizontal LinearLayout with gravity of left. Otherwise
almost same as first row.
Remember that horizontal is the default for android:orientation, so this attribute was omitted
for these two rows The colors will be explained later in this tutorial
Example Details
16
Horizontal LinearLayout.
That Layout then contains two more horizontal LinearLayouts.
The first (yellow) has android:layout_width of "wrap_content"
and android:gravity of "left". The second (green) has
android:layout_width of "match_parent" and android:gravity of
"right".

Example Details
17
Horizontal LinearLayout.
That Layout then contains three vertical nested layouts. The first
(blue) is a LinearLayout with android:orientation of "vertical" and
four Buttons inside. The second (violet) is a RadioGroup (similar to
LinearLayout but specific to enclosing RadioButtons and making
them mutually exclusive), also with android:orientation of "vertical".
It has four RadioButtons inside. The third is a LinearLayout with
android:orientation of "vertical" and four nested LinearLayouts
inside (details on next slide).
The first two columns (nested layouts) have android:layout_width
of "wrap_content", and the third has android:layout_width of
"match_parent".
Example Details
18
Vertical LinearLayout.
That Layout then contains four horizontal nested layouts. The
first (red) has android:gravity of "center_horizontal". The second
(orange) has android:gravity of "left". The third (yellow) has
android:gravity of "right". The fourth contains two further nested
horizontal LinearLayouts. The first (green) has
android:layout_width of "wrap_content" and android:gravity of
"left". The second (blue) has android:layout_width of
"match_parent" and android:gravity of "right".

Example Details
19
Button
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dp"
Button
© 2012 Marty Hall
Setting Colors
(& Localization Preview)

Colors
• Idea
– Although colors can be defined explicitly within layout file
(e.g., background="#ff0000"), usually more flexible to define
color names in separate file, so they can be changed all at
once. Refer to color with "@color/color_name".
• Syntax
<resources>
<color name="color_name_1">#rrggbb</color>
… 
</resources>
• Convention
– Use res/values/colors.xml
• However, any file name is legal. Sometimes it makes more
sense to define all attributes (strings, arrays, colors) of a View in
a single file dedicated to that view.
21
Color File
(res/values/colors.xml)
<resources>
<color name="color_1">#ff0000</color>
<color name="color_2">#ffa500</color>
<color name="color_3">#ffff00</color>
<color name="color_4">#008000</color>
<color name="color_5">#0000ff</color>
<color name="color_6">#ee82ee</color>
</resources>
22

Layout File
(res/layouts/nested_layouts.xml)
<LinearLayout xmlns:android="…"
<LinearLayout
android:background="@color/color_1">
...
</LinearLayout>

</LinearLayout>
23
Result
24

Localization Preview
• Idea
– You can store colors or other files in res/values-xy
instead of res/values. If the Locale is set to xy, then that
file is loaded after the files in res/values.
• If names match, later file overrides value from earlier file
• Usual approach
– Locale is set for entire phone by end user
• Approach used here
– Locale is set programmatically
• Many more details
– In later lecture on localization
25
Setting Locale Programmatically
• Usual purpose
– If user sometimes wants to run app in one language and
other times in a different language.
• Again, more common for end user to set Locale for entire
phone, not for individual apps.
• Purpose here
– Set the Locale to a fake value ("qq") just so that we can
replace colors.xml with another version that makes all the
background colors be black.
26

Setting Locale Programmatically
• Steps
Locale locale = new Locale("es"); // Language code
Locale.setDefault(locale);
Configuration config = new Configuration();
config.locale = locale;
context.getResources().updateConfiguration(config,
null);
– context above is reference to the main Activity
• More details
– http://adrianvintu.com/blogengine/post/
Force-Locale-on-Android.aspx
27
Project Layout
28
Sets color_1, color_2, …, color_6 to red, orange,
yellow, green, blue, and violet. Full text of this file
shown on earlier slide. Used if Locale is anything
other than "qq".
Sets all of color_1, color_2, …, color_6 to black.
Full text of this file shown on next slide. Used only
if Locale is "qq".

Localized Color File
(res/values-qq/colors.xml)
<resources>
</resources>
29
Main Java Code
public class NestedLayoutsActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.nested_layouts);
}
...
// Event handlers for bottom two Buttons
}
30
There are two buttons on initial screen that invoke this
same Activity. But, one sets the Locale to "qq" first.

Results
31
Locale set to
anything other than
"qq".
Locale set to "qq".
© 2012 Marty Hall
Layout Weight

Using android:layout_weight
• Idea
– Assign numbers for android:layout_weight. Sizes given are
proportional to those values.
• Steps (for heights)
– Assign android:layout_height to 0dp
– Use relative values for android:layout_weight
• For example, if you have three nested entries with
android:layout_weights of 1, 1, and 2, then they take up 25%,
25%, and 50% of the height of the parent.
– Analogous approach to set widths
• Common strategy
– Make the layout weights add up to 100, then treat them as
percents. So, use 25, 25, and 50 instead of 1, 1, and 2 in the
previous example. (Same effect, but clearer.)
33
Layout File
(res/layouts/layout_weights.xml)
<LinearLayout xmlns:android="…"
<TextView android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="30"
.../>
.../>
.../>
</LinearLayout>
34

Java Code
public class LayoutWeightsActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout_weights);
}
}
35
Results
36

© 2012 Marty Hall
RelativeLayout
RelativeLayout
• Idea
– Give ids to 1 or more key components (id="@+id/blah")
– Position other components relative to those components
• Most important XML attributes
– Aligning with container
• android:layout_alignParentBottom (and Top, Right, Left)
• android:layout_centerInParent (and centerHorizontal,
centerVertical)
– These all take "true" or "false" as values
– Aligning with other component
• android:layout_alignBottom (and Top, Right, Left)
• android:layout_toLeftOf (and toRightOf), android:layout_above
(and below)
– These all take existing ids as values
» android:layout_alignBlah="@id/existing_id" (@id, not @+id)
38

Referring to Existing IDs
• First component
– <Button id="@+id/button_1"
android:layout_alignParentRight="true" …/>
• Second component
– <Button android:layout_toLeftOf="@id/button_1" …/>
• Result
39
@+id for assigning a new id
@id (no +) for referring to an existing id
Button 1Button 2
Example Summary
40
<RelativeLayout
xmlns:android=

</RelativeLayout>

Example Details
41
TextView with width of match_parent and specific height.
Goes at top since I didn't say otherwise. Has id.
<TextView android:id="@+id/behind"
android:background="#ff0000"
android:textColor="#ffff00"
android:textSize="42dp"
android:text="Behind"
android:gravity="center"/>
<TextView android:layout_alignTop="@id/behind"
android:background="#00ffff"
android:textColor="#000000"
android:textSize="18dp"
android:text="On Top"
android:layout_marginTop="25dp"
android:layout_centerHorizontal="true"/>
TextView with android:layout_alignTop referring to first
component. Moved down via android:layout_marginTop
Example Details
42
Button with android:layout_alignParentBottom="true" and
android:layout_alignParentRight="true". Has an id. Has width of
wrap_content. This is the first Button defined.
Button with android:layout_alignBottom and android:layout_toLeftOf
referring to image button. Has width of wrap_content.
EditText with android:layout_above referring to image
button. Has width of match_parent.
<Button android:id="@+id/image_button"
android:text="Search Images"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"/>
<Button android:layout_alignBottom="@id/image_button"
android:layout_toLeftOf="@id/image_button"
android:text="Search Web"/>
<EditText android:layout_width="match_parent"
android:layout_above="@id/image_button"
android:layout_alignRight="@id/image_button"/>

© 2012 Marty Hall
TableLayout
TableLayout
• Idea
– Put widgets or nested layouts in a grid. No borders.
– Like HTML tables, the number of rows and columns is
determined automatically, not explicitly specified.
– Components are usually placed inside TableRow
• Most important XML attributes (TableLayout)
– android:stretchColumns
• An index or comma-separated list of indexes. Specifies the
column or columns that should be stretched wider if the table is
narrower than its parent. Indexes are 0-based.
– android:shrinkColumns
• Column(s) that should be shrunk if table is wider than parent.
– android:collapseColumns
• Column(s) to be totally left out. Can be programmatically put
back in later.
44

TableRow
• Idea
– Goes inside TableLayout to define a row.
• Technically, elements between rows are permitted, but you can
achieve same effect with a TableRow and android:layout_span.
• Most important XML attributes of elements
inside a TableRow
– android:layout_column
• Normally, elements are placed in left-to-right order. However,
you can use android:layout_column to specify an exact column,
and thus leave earlier columns empty.
– android:layout_span
• The number of columns the element should straddle.
Like colspan for HTML tables.
• There is nothing equivalent to HTML’s rowspan; you must use
nested tables instead. See example.
45
Example Summary
46
<TableLayout
xmlns:android=
android:layout_height="match_parent"
android:stretchColumns="1">
<TableRow>…</TableRow>
…
</TableLayout>
This is why the middle
column is wider than the
other two columns.

Example Details
47
Two TableRows, each with 3 Buttons. No special options.
<TableRow>
<Button android:text="Button 0"/>
</TableRow>
<TableRow>
</TableRow>
Example Details
48
Button 7 uses android:layout_column="2". So, there is no
entry at all for the middle column.
<TableRow>
<Button android:text="Button 7"
android:layout_column="2"/>
</TableRow>
<TableRow>
android:layout_span="2"/>
</TableRow>
Button 9 uses android:layout_span="2".

Example Details
49
A nested table. Uses android:layout_span="2" so that it straddles
two columns of the main table. Uses android:stretchColumns="1"
so that the second column fills available space.
A Button. android:layout_height is match_parent so that it is the
same height as table to its left. There is no option similar to HTML’s
colspan, so nested tables are needed to achieve this effect.
<TableRow>
<TableLayout xmlns:android="…"
android:layout_span="2"
android:stretchColumns="1">
<TableRow>
</TableRow>
<TableRow>
</TableRow>
</TableLayout>
android:layout_height="match_parent"/>
</TableRow>
© 2012 Marty Hall
The Hierarchy Viewer

Hierarchy Viewer
• Idea
– The Android distribution includes a program called
hieararchyviewer that will show a graphical
representation of Views and sub-Views. Useful for
debugging and understanding nested layouts.
• Details
– Start app in emulator. Go to screen of interest.
– Go to android-sdk/tools (or, put this in your PATH)
– Type hierarchyviewer
– Click on Focused Window,
then press Load View
Hierarchy button
– Explore!
51
Hierarchy View for
RelativeLayout Example
52
Click on an entry to show which part of screen it corresponds to,
and to get details about the XML attributes.
Details: http://developer.android.com/guide/developing/debugging/debugging-ui.html

© 2012 Marty Hall
Wrap-Up
Other Layouts
• AbsoluteLayout
– From older versions; now deprecated; use RelativeLayout
• FrameLayout
– For formatting a single item. Usually used explicitly with
TabHost. Used internally by other layouts.
• TabHost
– Combines tabs with switching Activities. Covered in later
lecture on Intents and Activity switching.
• ListView and GridView
– Not generalized layouts, but have somewhat similar role.
Covered in later lecture.
54

More Reading
• Tutorial: Declaring Layout
– http://developer.android.com/guide/topics/ui/
declaring-layout.html
• Tutorial: Hello Views
– http://developer.android.com/resources/tutorials/views/
• Has sub-sections on LinearLayout, RelativeLayout, and
TableLayout
• Chapter: Working with Containers
– From The Busy Coder’s Guide to Android Development
by Mark Murphy.
• http://commonsware.com/Android/
• Chapter: User Interface Layout
– From The Android Developer’s Cookbook by Steele & To55
Summary
• LinearLayout
– Ideas
• One row or one column.
• Nesting is key window-layout strategy
– Key XML attributes
• android:orientation, android:layout_weight
• RelativeLayout
– Idea
• Position later component relative to earlier one
– Key XML attributes
• android:layout_alignBottom (and similar),
android:layout_toLeftOf (and similar)
• TableLayout
– Idea
• Put components in a grid
– Key XML attributes for entries inside TableRow
• android:layout_column, android:layout_span56

© 2012 Marty Hall
Questions?
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Android layouts

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