Android studio Default Activity not found

Question

After i have created my own appplication class:

package com.example.bezzabarovaa.myapplication;
import android.app.Application;
import android.content.Context;

/**
 * Created by bezzabarovaa on 04.08.2017.
 */

public class app extends Application {
public static Context context;

@Override public void onCreate() {
    super.onCreate();
    context = getApplicationContext();
}

}

and have changed manifest.xml (changed application to app class)

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.bezzabarovaa.myapplication">

<app
    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">
    <activity android:name=".MainActivity"
        android:label = "@string/app_name">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

I`ve got a message Error running Unnamed: Default Activity not found

If I will change my classapp back to application in manifest.xml - everything is ok. Where is a problem? Thank you.

Answer 1

This <app is supposed to be <application you specify your custom app in here:

<application android:name=".app" ...

Check the documentation the name section says:

The fully qualified name of an Application subclass implemented for the application. When the application process is started, this class is instantiated before any of the application's components. The subclass is optional; most applications won't need one. In the absence of a subclass, Android uses an instance of the base Application class.

Full example (with your code):

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.bezzabarovaa.myapplication">

<application
    android:name=".app"
    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">
    <activity android:name=".MainActivity"
        android:label = "@string/app_name">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

Answer 2

Solved by clicking the "Sync project with gradle files"