How to fix You need to use a Theme AppCompat theme or descendant with this activity

Question

I am having trouble running my Android app in a fullscreen mode per instructions of a video  When it tries to run  the app crashes with the error    You need to use a Theme AppCompat theme  or descendant  with this activity  Manifest File   lt  xml version  1 0  encoding  utf-8   gt   lt manifest xmlns android  http   schemas android com apk res android  package  com djsg38 hikerswatch  gt    lt uses-permission android name  android permission ACCESS FINE LOCATION    gt   lt uses-permission android name  android permission ACCESS COARSE LOCATION    gt   lt uses-permission android name  android permission INTERNET    gt    lt application     android allowBackup  true      android icon   mipmap ic launcher      android label   string app name      android supportsRtl  true      android theme   style AppTheme  gt       lt activity android name   MainActivity          android theme   android style Theme NoTitleBar Fullscreen   gt           lt intent-filter gt               lt action android name  android intent action MAIN    gt                lt category android name  android intent category LAUNCHER    gt           lt  intent-filter gt       lt  activity gt   lt  application gt    lt  manifest gt    Styles File   lt resources gt    lt  -- Base application theme  -- gt   lt style name  AppTheme  parent  Theme AppCompat Light DarkActionBar  gt       lt  -- Customize your theme here  -- gt       lt item name  colorPrimary  gt  color colorPrimary lt  item gt       lt item name  colorPrimaryDark  gt  color colorPrimaryDark lt  item gt       lt item name  colorAccent  gt  color colorAccent lt  item gt   lt  style gt      Partial MainActivity that may be useful  public class MainActivity extends AppCompatActivity

User · Accepted Answer

Your application has an AppCompat theme

<application
    android:theme="@style/AppTheme">

But, you overwrote the Activity (which extends AppCompatActivity) with a theme that isn't descendant of an AppCompat theme

<activity android:name=".MainActivity"
    android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >

You could define your own fullscreen theme like so (notice AppCompat in the parent=)

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

Then set that on the Activity.

<activity android:name=".MainActivity"
    android:theme="@style/AppFullScreenTheme" >

Note: There might be an AppCompat theme that's already full screen, but don't know immediately

User · Answer

u should add a theme to ur all activities  u should add theme for all application in ur  lt application gt  in ur manifest  but if u have set different theme to ur activity u can use     android theme   style Theme AppCompat    or each kind of AppCompat theme

User · Answer

Used to face the same problem  The reason was in incorrect context passing to AlertDialog Builder here   use like AlertDialog Builder Homeactivity this

User · Answer

If you add the android theme   style Theme AppCompat Light  to  lt application gt  in AndroidManifest xml file  problem is solving

[android] How to fix: "You need to use a Theme.AppCompat theme (or descendant) with this activity"

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