怎么使用V7包中ActionBar

============问题描述============

本人严格按照android官网的步骤 导入 android-support-v7-appcompat 库项目，再新建了一个工程，引入这个库项目，编译没问题。

但是一运行却报如下问题 ，

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.actionbarlower/com.example.actionbarlower.MainActivity}: java.lang.NullPointerException

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)

at android.app.ActivityThread.access$700(ActivityThread.java:159)

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)

at android.os.Handler.dispatchMessage(Handler.java:99)

at android.os.Looper.loop(Looper.java:176)

at android.app.ActivityThread.main(ActivityThread.java:5419)

at java.lang.reflect.Method.invokeNative(Native Method)

at java.lang.reflect.Method.invoke(Method.java:525)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)

at dalvik.system.NativeStart.main(Native Method)

Caused by: java.lang.NullPointerException

at android.support.v7.app.ActionBarImplICS.setDisplayShowHomeEnabled(ActionBarImplICS.java:169)

at android.support.v7.app.ActionBarImplJB.setDisplayShowHomeEnabled(ActionBarImplJB.java:20)

at com.example.actionbarlower.MainActivity.onCreate(MainActivity.java:20)

at android.app.Activity.performCreate(Activity.java:5372)

at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)

... 11 more

代码如下：

public class MainActivity extends ActionBarActivity {

private ActionBar supportActionBar;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

supportActionBar = getSupportActionBar();

supportActionBar.setDisplayShowHomeEnabled(true);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

getMenuInflater().inflate(R.menu.main, menu);

return super.onCreateOptionsMenu(menu);

}

}

manifest如下 :

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.example.actionbarlower"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk

android:minSdkVersion="8"

android:targetSdkVersion="9" />

<application

android:allowBackup="true"

android:icon="@drawable/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

<activity

android:name="com.example.actionbarlower.MainActivity"

android:label="@string/app_name"

android:theme="@style/Theme.AppCompat.Light" >

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

</manifest>

空指针指向的是 ： supportActionBar.setDisplayShowHomeEnabled(true); 这行，但是我在前面打印supportActionBar 并不是空的。

============解决方案1============

android:minSdkVersion和android:targetSdkVersion分别换成10和15试试看