ActionBar 空指针异常

1. 加载完视图后，再去获取：

写在setContentView()后面。

2.sdk版本：

Actionbar的主题在3.0以后才有，使用的时候要确保，最低的版本不能小于3.0。

<uses-sdk
        android:minSdkVersion="11"
        android:targetSdkVersion="17" />

3.配置清单中，添加的主题：

android:theme="@style/AppTheme" >

其父主题要具有ActionBar，例如：

<style name="AppTheme" parent="@android:style/Theme.Holo.Light">

或者：

    <!--
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Light">
        <!--
            Theme customizations available in newer API levels can go in
            res/values-vXX/styles.xml, while customizations related to
            backward-compatibility can go here.
        -->
    </style>

    <!-- Application theme. -->
    <style name="AppTheme" parent="AppBaseTheme">
        <!-- All customizations that are NOT specific to a particular API-level can go here. -->
    </style>

4.活动类及其父类中，不要设置为全屏：

//getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

5.没有引用到v11+包中的主题。

所以，如果遇到报空的问题，你看看你的工程中有没有values-v11或者v14的包，没有的话就去其他工程中copy一份过来，改下就可以了。

1）values      --> styles.xml
  <!--
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Light">
        <!--
            Theme customizations available in newer API levels can go in
            res/values-vXX/styles.xml, while customizations related to
            backward-compatibility can go here.
        -->
    </style>

2）values-v11  --> styles.xml
   <!--
        Base application theme for API 11+. This theme completely replaces
        AppBaseTheme from res/values/styles.xml on API 11+ devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Holo.Light">
        <!-- API 11 theme customizations can go here. -->
    </style>

3）values-v14  --> styles.xml
  <!--
        Base application theme for API 14+. This theme completely replaces
        AppBaseTheme from BOTH res/values/styles.xml and
        res/values-v11/styles.xml on API 14+ devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Holo.Light.DarkActionBar">
        <!-- API 14 theme customizations can go here. -->
    </style>