安卓报错：java.lang.RuntimeException: Unable to start activity ComponentInfo---getSupportActionBar()为null

叁歲伎倆 2022-11-27 06:29 184阅读 0赞

报错信息：

E/AndroidRuntime: FATAL EXCEPTION: main
        Process: com.example.edm, PID: 16919
        java.lang.RuntimeException: Unable to start activity ComponentInfo{ com.example.edm/com.example.edm.StudentActivity.TimeTable.ui.editcourse.EditActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3773)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3952)
            at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
            at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
            at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2386)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:213)
            at android.app.ActivityThread.main(ActivityThread.java:8169)
            at java.lang.reflect.Method.invoke(Native Method)
            at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101)
         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at com.example.edm.StudentActivity.TimeTable.ui.editcourse.EditActivity.setActionBar(EditActivity.java:248)
            at com.example.edm.StudentActivity.TimeTable.ui.editcourse.EditActivity.onCreate(EditActivity.java:75)
            at android.app.Activity.performCreate(Activity.java:8086)
            at android.app.Activity.performCreate(Activity.java:8074)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1313)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3746)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3952) 
            at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91) 
            at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149) 
            at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2386) 
            at android.os.Handler.dispatchMessage(Handler.java:107) 
            at android.os.Looper.loop(Looper.java:213) 
            at android.app.ActivityThread.main(ActivityThread.java:8169) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101)

错误原因：

private void setActionBar() { 
            ActionBar actionBar = getSupportActionBar();
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setTitle(R.string.course_edit);
        }

代码中actionBar为空指针。

解决方案：检查AndroidManifest.xml文件中相关Activity的theme是否为:

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

将其改为：

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