无法在 android studio 上启动应用程序是否显示 java.lang.NullPointerException：

Question

应用程序未启动。我看过 youtube 的启动画面教程

<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"
    tools:context=".MainActivity"
    android:background="#fece2f">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginTop="104dp"
        android:layout_marginEnd="10dp"
        android:contentDescription="@string/todo"
        android:src="@drawable/logo"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="496dp"
        android:fontFamily="@font/bangers"
        android:text="@string/TARZERA"
        android:textAlignment="center"
        android:textSize="70sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="@font/antic"
        android:text="@string/Manifacturer_of_Scarves_Stoles"
        android:textAlignment="center"
        android:textSize="18sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

这里是主要活动

</androidx.constraintlayout.widget.ConstraintLayout>


    {
   private static int SPLASH_SCREEN = 5000;

    //variables
    Animation topAnim, bottomAnim;
    ImageView imageView;
    TextView logo, slogan;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.activity_main);

        //Animations
        topAnim  = AnimationUtils.loadAnimation(this,R.anim.top_animation);
        bottomAnim = AnimationUtils.loadAnimation(this,R.anim.bottom_animation);

        //Hooks

        imageView = findViewById(R.id.imageView);
        logo = findViewById(R.id.textView);
        slogan = findViewById(R.id.textView2);

        imageView.setAnimation(topAnim);
         logo.setAnimation(bottomAnim);
        slogan.setAnimation(bottomAnim);

        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent intent = new Intent(MainActivity.this,Dashboard.class);
                startActivity(intent);
                finish();
            }
        },SPLASH_SCREEN);
    }
}


    <?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">

    <translate
        android:fromXDelta="0%"
        android:fromYDelta="-50%"
        android:duration="2000"/>
    <alpha
        android:fromAlpha="0.1"
        android:toAlpha="1.0"
        android:duration="1500"/>
</set>




  <?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">

    <translate
        android:fromXDelta="0%"
        android:fromYDelta="100%"
        android:duration="1500"/>
    <alpha
        android:fromAlpha="0.1"
        android:toAlpha="1.0"
        android:duration="1500"/>
</set>

主要问题是我现在无法在模拟器中启动应用程序，也尝试了一切以使其工作但仍然无法成功。启动应用程序时，它显示一长串错误，但没有一个是任何编码错误，而是启动问题

Answer 1

在您的 xml 文件中，您将 textviews 的 ID 指定为 textView2 和 textView3。但是在您的 java 文件中，您将 id 设置为 textView 和 textView2。所以，改变那两行。

logo = findViewById(R.id.textView2);
slogan = findViewById(R.id.textView3);