在Android中使用主题(Theme)和风格(Style)

主题是由一组应用到整个应用程序中的风格构成的。主题定义了应用程序中的各种外观。android中引入了主题和风格的概念。风格可以被应用到一个视图(View)，而主题只能用到整个应用程序。

风格(Styles):

Styles are defined as xml resources files in  directory of your project.

consider this definition of a TextView:

风格(Styles)用xml文件的格式定义，这些文件存放在工程项目中的res/values目录下。

以下是一个TextView的定义：

 

  

   

    Cpp代码  
    
   
  
  
<TextView    android:layout_width="fill_parent"  
     android:layout_height="wrap_content"  
     android:textColor="#FFF"  
     android:typeface="monospace"  
     android:text="First Text View"  
     android:background="#00F"  
     />  
 
 

以上代码定义了一个TextView，包括文本框的宽度和高度，字体大小，字体格式，并且设置了蓝背景。

如果我们想用风格来实现同样的效果，我们首先要定义一个

this defines a text view with width and height equal to wrap_content, white font color, font type “monospace” and blue back ground.

if we want to have the same results using a style: we first create a xml file (call it styles.xml) inres/values directory and it would be like this:

 

  

   

    Xml代码  
    
   
  
  
<?xml version="1.0" encoding="utf-8"?>  
<resources>  
<style name="BlueLabel">  
<item name="android:layout_width">fill_parent</item>  
<item name="android:layout_height">wrap_content</item>  
<item name="android:typeface">monospace</item>  
<item name="android:background">#00F</item>  
<item name="android:textColor">#FFF</item>  
</style>  
</resources>  
 
 

then redefine the TextView like this:

 

  

   

    Xml代码  
    
   
  
  
<TextView android:text="First Text View"  
     style="@style/BlueLabel"  
     />  
 
 

and you will receive the same results.
the attributes in the <item>tag can be any layout property.

Inheriting Styles:

Styles in Android has an interesting feature which is the ability to inherit styles in a fashion similar to that in CSS. consider this example:

we have a style for a button like this:

 

  

   

    Xml代码  
    
   
  
  
<style name="ButtonStyle">  
<item name="android:layout_width">wrap_content</item>  
<item name="android:layout_height">wrap_content</item>  
<item name="android:textSize">15px</item>  
<item name="android:typeface">serif</item>  
</style>  
 
 

the button will appear like this:

we can make this style inherit from BlueLabel defined previously by adding the parent attribute to the <style*gt; tag:

 

  

   

    Xml代码  
    
   
  
  
<style name="ButtonStyle" parent="BlueLabel">  
 
 

then the button will be like this:

the button inherited the background color from the parent style.

another interesting feature in styles inheritance is the ability to inherit from the platform built-in styles defined in the android.R.style namespace. to know more about the platform styles check this link

or you can type in your editor (Eclipse) android.R.style and let the intelli-sense list you the complete list of platform styles, if you want to use them in your xml just replace the undrscores with a period like this:
Widget_Button becomes @android:style/Widget.Button.

In the previous button style example we will set the parent of the style to be@android:style/Widget.Button.Small
and the button will be like this:

Note: if you apply a style to a ViewGroup widget, it’s child widgets will not inherit that style.

Using Themes:

you can apply styles as themes on an activity level or application level.

if you apply a theme on an activity level then all widgets within that activity will inherit from that theme.
to do so, open the AndroidManifest.xml and go the <activity> tag and add theandroid:theme attribute:

 

  

   

    Xml代码  
    
   
  
  
<activity android:name=".StylesDemo"  
                  android:label="@string/app_name" android:theme="@style/BlueLabel">  
 
 

to apply a theme on the application level so that the style will be applied to all activities within your application, open the AndroidManifest.xml and go the <application> tag and add theandroid:theme attribute:

<application android:icon="@drawable/icon" android:label="@string/app_name" android:theme="@style/BlueLabel">

to set the theme of an activity programmatically call this line in the onCreate method

this.setTheme(R.style.BlueLabel);

and that’s was all about using themes and styles in Android, stay tuned for another topic next week.