Question

我正在使用Theme.AppCompat.Light.DarkActionBar，并且在扩展AppCompatActivity的主要活动中，我得到的ActionBar完全符合预期。在另一个也延伸AppCompatActivity的活动中，我在活动加载时遇到这些错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{activity2}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setBackgroundDrawable(android.graphics.drawable.Drawable)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2306)
        at     android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366)
        at android.app.ActivityThread.access$800(ActivityThread.java:149)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5290)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setBackgroundDrawable(android.graphics.drawable.Drawable)' on a null object reference
        at com.nick.simplequiz.TabletGallery.onCreate(TabletGallery.java:53)
        at android.app.Activity.performCreate(Activity.java:6020)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2259)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366)
            at android.app.ActivityThread.access$800(ActivityThread.java:149)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5290)

错误是由以下行引起的：

ActionBar bar = getActionBar();
    bar.setBackgroundDrawable(new ColorDrawable(0xff01579b));
    bar.setDisplayShowTitleEnabled(false);
    bar.setDisplayShowTitleEnabled(true);

如果没有这些行导致错误，活动将会运行并且操作栏不可见。为什么使用此主题时操作栏不可见？

Answer 1

使用getSupportActionBar()在AppCompatActivity：

中获取ActionBar

ActionBar bar = getSupportActionBar();
bar.setBackgroundDrawable(new ColorDrawable(0xff01579b));
bar.setDisplayShowTitleEnabled(false);
bar.setDisplayShowTitleEnabled(true);

使用Theme.AppCompat.Light.DarkActionBar时不会出现ActionBar

1 个答案: