运行“RegistrationActivity”时出错：必须导出活动或包含意图过滤器

Question

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I can't run my registrationActivity as it gives me the error:

The activity must be exported or contain an intent-filter

And I don't know how to solve, what should I put in my android manifest?

Also, I'm getting java.lang.NullPointerException with the if below:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_registration);

    mAuth = FirebaseAuth.getInstance();
    firebaseAuStateListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            final FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
            if (user != null){
                Intent intent = new Intent(RegistrationActivity.this, MainActivity.class);
                startActivity (intent);
                finish();
                return;
            }
        }
    }
}

Answer 1

put it in your androidmanifest.xml

inside the application tag

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

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