Declare receiver here

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:dist="http://schemas.android.com/apk/distribution"
   package="com.demo.widgets">

   <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/AppTheme">
       <receiver android:name=".MyWidget">
           <intent-filter>
               <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
           </intent-filter>

           <meta-data
               android:name="android.appwidget.provider"
               android:resource="@xml/my_widget_info" />
       </receiver>

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

</manifest>