"You need to use a Theme.AppCompat theme (or descendant) with this activity." [duplicate]

Question

I am new to Android programming and I am running into a simple XML issue. I am in the process of trying to make one of my empty activities into a fullscreen activity. I tried adding this line of code android:theme="@android:style/Theme.NoTitleBar.Fullscreen" into my android manifest file, which ended up making my app crash on start.

If this also helps, my java file for the affected activity extends the AppCompatActivity. I saw some other posts that mentioned that this would create issues but I have not been able to fix my problem.

Please help me fix this issue while still making the activity fullscreen. Any help is appreciated. Thanks!

XML

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/Theme.AppCompat.Light">
    <activity android:name=".MainActivity"
        android:label="Marks Calculator">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.APP_CALCULATOR" />
        </intent-filter>
    </activity>
    <activity android:name=".Home_Activity"
        android:label="Finite Time Manager">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.HOME" />
        </intent-filter>
    </activity>
    <activity
        android:name=".Welcome_Activity"
        android:theme="@android:style/Theme.NoTitleBar.Fullscreen">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
        </activity>
</application>

Error logcat

12-22 12:21:30.214 32475-32475/com.managergmail.time.finite.finitemanager02 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.managergmail.time.finite.finitemanager02, PID: 32475
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.managergmail.time.finite.finitemanager02/com.managergmail.time.finite.finitemanager02.Welcome_Activity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2581)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2647)
    at android.app.ActivityThread.-wrap11(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1502)
    at android.os.Handler.dispatchMessage(Handler.java:111)
    at android.os.Looper.loop(Looper.java:207)
    at android.app.ActivityThread.main(ActivityThread.java:5763)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)
    Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
    at android.support.v7.app.AppCompatDelegateImplV9.createSubDecor(AppCompatDelegateImplV9.java:359)
    at android.support.v7.app.AppCompatDelegateImplV9.ensureSubDecor(AppCompatDelegateImplV9.java:328)
    at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289)
    at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
    at com.managergmail.time.finite.finitemanager02.Welcome_Activity.onCreate(Welcome_Activity.java:17)
    at android.app.Activity.performCreate(Activity.java:6280)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1116)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2534)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2647)
    at android.app.ActivityThread.-wrap11(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1502)
    at android.os.Handler.dispatchMessage(Handler.java:111)
    at android.os.Looper.loop(Looper.java:207)
    at android.app.ActivityThread.main(ActivityThread.java:5763)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)

Answer 1

Your Welcome_Activity probably extends AppCompatActivity so the theme should be appcompat theme.

In your styles.xml file put this:

<style name="AppTheme.FullScreen" parent="@style/Theme.AppCompat.Light">
    <item name="windowNoTitle">true</item>
    <item name="windowActionBar">false</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowContentOverlay">@null</item>
</style>

Now you can use this theme:

<activity
    android:name=".Welcome_Activity"
    android:theme="@style/AppTheme.FullScreen">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

This will apply fullscreen theme for this particular activity. If you want full screen for whole application you can just replace the application theme in manifest with this theme.

Answer 2

The theme you currently selected (in the welcome activity) isn´t a appcompat theme. This one should for example work: '

@style/Theme.AppCompat.Light.NoActionBar.FullScreen