java Android后退按钮

Question

我试图在左上角的操作栏中创建一个back，但它一直让我出现空指针异常，我不知道为什么这里有我的代码

这是显示后屏幕的类

    ActionBar bar = getActionBar();
    //for color
    bar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#5c7afe")));


    // TODO Auto-generated method stub

    super.onCreate(savedInstanceState);
    setContentView(R.layout.company_info1);
     // get the action bar
    安卓.app.ActionBar actionBar = getActionBar();


    // Enabling Back navigation on Action Bar icon
    actionBar.setDisplayHomeAsUpEnabled(true);

这是我的清单文件

      <activity 安卓:name="com.example.hotlinesegypt.company_info"
        安卓:parentActivityName="com.example.hotlinesegypt.Company" >

这是我的原木猫

08-21 15:51:32.614: E/AndroidRuntime(16777): FATAL EXCEPTION: main
08-21 15:51:32.614: E/AndroidRuntime(16777): Process: mo.hot.hotlinak, PID: 16777
08-21 15:51:32.614: E/AndroidRuntime(16777): java.lang.RuntimeException: Unable to start activity ComponentInfo{mo.hot.hotlinak/com.example.hotlinesegypt.Company}: java.lang.NullPointerException
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread.access$900(ActivityThread.java:161)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.os.Handler.dispatchMessage(Handler.java:102)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.os.Looper.loop(Looper.java:157)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread.main(ActivityThread.java:5356)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at java.lang.reflect.Method.invokeNative(Native Method)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at java.lang.reflect.Method.invoke(Method.java:515)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at dalvik.system.NativeStart.main(Native Method)
08-21 15:51:32.614: E/AndroidRuntime(16777): Caused by: java.lang.NullPointerException
08-21 15:51:32.614: E/AndroidRuntime(16777):    at com.example.hotlinesegypt.Company.onCreate(Company.java:46)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.Activity.performCreate(Activity.java:5426)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
08-21 15:51:32.614: E/AndroidRuntime(16777):    at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269)

Answer 1

在我看来，您刚刚在这一行混淆了变量名，您创建了名为bar的ActionBar变量

ActionBar bar = getActionBar();

然后在这里将其称为actionBar：

actionBar.setDisplayHomeAsUpEnabled(true);

将此行更改为：

bar.setDisplayHomeAsUpEnabled(true);

这看起来像是什么，但你们需要检查公司的第46行，看看它是否符合我的建议