xml


Using styles on Android layouts 1

A very cool feature of Android that many developers do not know (at least me 6 months ago) is the possibility of using “styles” on Android XML layouts. This thing is similar to CCS on HTML and provides a method to simplify the XML design.

First, let’s see an example of a XML layout without styles, you can notice the need to repeat attributes and the difficulty of reading the XML:

<LinearLayout
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:orientation="vertical">
 <TextView
  android:text="@string/text1"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:textStyle="bold"
  android:textColor="@color/white"
 />
 <TextView
  android:text="@string/text2"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:textStyle="bold"
  android:textColor="@color/red"
 />
</LinearLayout>

But we can define styles grouping this attributes on the file res/values/styles.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <style name="VerticalLinearLayout">
  <item name="android:layout_width">wrap_content</item>
  <item name="android:layout_height">wrap_content</item>
  <item name="android:orientation">vertical</item>
 </style>
 <style name="WhiteText">
  <item name="android:layout_width">wrap_content</item>
  <item name="android:layout_height">wrap_content</item>
  <item name="android:orientation">vertical</item>
  <item name="android:textStyle">bold</item>
  <item name="android:textColor">@color/white</item>
 </style>
 <style name="RedText" parent="@style/WhiteText">
  <item name="android:textColor">@color/red</item>
 </style>
</resources>

Note te possibility of  inheriting styles, in this example “RedText” is inherited from the “WhiteText” style changing only the text color.

Our XML layout, with styles, gets reduced to:

<LinearLayout style="@style/VerticalLinearLayout"/>
 <TextView style="@style/WhiteText"
  android:text="@string/text1"
 />
 <TextView style="@style/RedText"
  android:text="@string/text2"
 />
</LinearLayout>

Finally,  you can see that I’m using colors (@color/white and @color/red) which must be defined on the file res/values/colors.xml (in a similar way to strings):

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <color name="white">#ffffffff</color>
 <color name="red">#ffff0000</color>
</resources>