Android - onClickListener NullPointerException

Question

Здравствуйте, пользователи Stackoverflow, Я пытаюсь создать намерение при нажатии кнопки, чтобы изменить свою активность в приложении для Android, которое я разрабатываю на Java. Однако я просто получаю исключение NullPointerException:

Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at .onCreate(MainActivity.java:32) - Line 32 is the Line with  "button_get_started.setOnClickListener(new View.OnClickListener(){"

Кто-нибудь знает, как решить эту проблему или как ее обойти? Спасибо за вашу помощь:)

Основной код:

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

//Splash Activity
public class MainActivity extends AppCompatActivity {

    //Attributes
    ImageView imageView_thisfit;
    ImageView imageView_logo;
    public Button button_get_started;




    //Methods

    //This method is executed while creating an instance of the Activity
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        imageView_thisfit = findViewById(R.id.imageView_thisfit);
        imageView_logo = findViewById (R.id.imageView_logo);
        button_get_started = findViewById(R.id.button_get_started);
        button_get_started.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openRegistrationActivity();
            }
        });

        setContentView(R.layout.activity_splash);
    } //onCreate



    public void openRegistrationActivity(){
        Intent intent = new Intent(MainActivity.this, RegistrationActivity.class);
        startActivity(intent);
    }

А вот мой XML-файл:

    <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background"
    tools:context=".MainActivity">

    <!-- thisFIT -->
    <ImageView
        android:id="@+id/imageView_thisfit"
        android:layout_width="205dp"
        android:layout_height="101dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.18"
        app:srcCompat="@drawable/thisfit" />

    <!-- Logo -->
    <ImageView
        android:id="@+id/imageView_logo"
        android:layout_width="218dp"
        android:layout_height="246dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView_thisfit"
        app:srcCompat="@drawable/logo" />

    <!-- GET STARTED -->
    <Button
        android:id="@+id/button_get_started"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:background="@drawable/bg"
        android:text="GET STARTED"
        android:textSize="20sp"
        android:textColor="#FFFFFFFF"
        android:fontFamily="@font/dosis"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.495"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView_logo"
        app:layout_constraintVertical_bias="0.23000002" />

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

Просто переместите эту строку

setContentView(R.layout.activity_splash);

при запуске метода onCreate ().

Как это: -

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_splash);

    imageView_thisfit = findViewById(R.id.imageView_thisfit);
    imageView_logo = findViewById (R.id.imageView_logo);
    button_get_started = findViewById(R.id.button_get_started);
    button_get_started.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            openRegistrationActivity();
        }
    });
}

Answer 2

Переместить линию setContentView(R.layout.activity_splash); ниже super.onCreate(savedInstanceState);

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splash);

        imageView_thisfit = findViewById(R.id.imageView_thisfit);
        imageView_logo = findViewById (R.id.imageView_logo);
        button_get_started = findViewById(R.id.button_get_started);
        button_get_started.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openRegistrationActivity();
            }
        });


    }