Exception information

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lwm.myapplication/com.lwm.myapplication.MainActivity}

Java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.

Exception screenshot

Anomaly analysis

The exception means: you need to use a theme.appcompat theme (or descendant) with this activity. Why this happens is because Activity inherits AppCompatActivity, as follows:

public class MainActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

But the appTheme I use is the theme of the normal Activity, so an error will be reported. The error message requires us to use the theme (or descendant) that inherits theme.appcompat.

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@android:style/Theme.NoTitleBar.Fullscreen">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
 
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

Exception resolution

The first method: change the theme so that the theme inherits fromtheme.appcompat.xxx

 
This is an AppTheme that is automatically created when we create a new project. Note that it is inherited from Theme.AppCompat.xxx

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

The second method: change the inheritance of the class from AppCompatActivity to Activity or FragmentActivity.

public class MainActivity extends Activity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

Reprinted: