移除theme.material中的动作栏时出错

Question

我是开发移动应用程序的新手，我正在使用android studio。我试图删除操作栏，但每次我试图将主题更改为NoActionBar时，出现以下错误:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ruleteacher/com.example.ruleteacher.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.hide()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.hide()' on a null object reference
at com.example.ruleteacher.LoginActivity.onCreate(LoginActivity.java:38)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:193) 
at android.app.ActivityThread.main(ActivityThread.java:6669) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

我试过使用getSupportActionBar().hide();，它确实删除了操作栏，但仍然有这个空白的空间分配给操作栏。帮我把这个地方移开，谢谢。主题XML文件

<resources xmlns:tools="http://schemas.android.com/tools">
<!-- Base application theme. -->
<style name="Theme.RULETeacher" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
<!-- Primary brand color. -->
<item name="colorPrimary">@color/purple_500</item>
<item name="colorPrimaryVariant">@color/purple_700</item>
<item name="colorOnPrimary">@color/white</item>
<!-- Secondary brand color. -->
<item name="colorSecondary">@color/teal_200</item>
<item name="colorSecondaryVariant">@color/teal_700</item>
<item name="colorOnSecondary">@color/black</item>
<!-- Status bar color. -->
<item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
<!-- Customize your theme here. -->
</style>
</resources>

android manifest文件'

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.RULETeacher">
<activity android:name=".MainActivity3"></activity>
<activity android:name=".MainActivity2" />
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".SignUpActivity" />
<activity
android:name=".MainActivity"
android:label="@string/app_name" />
</application>

Answer 1

use

<style name="Theme.RULETeacher" parent="Theme.MaterialComponents.DayNight.NoActionBar">

不是

<style name="Theme.RULETeacher" parent="Theme.MaterialComponents.DayNight.DarkActionBar">

并将其从代码

中删除

getSupportActionBar().hide();

不要放任何与操作栏相关的方法