В чем может быть проблема с этим кодом Java и XML?

Question

Получаю исключение нулевого указателя после установки прослушивателей onclick для просмотра текста и кнопки. Где может быть ошибка, пожалуйста?

Файл MainActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:gravity="center"
    android:orientation="vertical"
    android:background="@drawable/background_design"
    tools:context=".MainActivity">


    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="Login"
                android:textAppearance="?android:textAppearanceLarge"
                android:textColor="#ffffff"></TextView>

            <EditText
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="Enter your email..."
                android:textColorHint="@android:color/white"
                android:textColor="#ffffff"
                android:background="@drawable/ed_design"
                android:padding="10dp"
                android:inputType="textEmailAddress"
                android:layout_margin="10dp"
                android:id="@+id/email_login"></EditText>

            <EditText
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="Enter your password..."
                android:textColorHint="@android:color/white"
                android:textColor="#ffffff"
                android:background="@drawable/ed_design"
                android:padding="10dp"
                android:layout_margin="10dp"
                android:inputType="textPassword"
                android:id="@+id/pass_login"></EditText>

            <Button
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:id="@+id/login_button"
                android:text="Login"
                android:textAllCaps="false"
                android:background="@drawable/ed_design"
                android:padding="10dp"
                android:textColor="@android:color/white"
                android:textAppearance="?android:textAppearanceMedium"
                android:layout_margin="10dp"></Button>

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:textAppearance="?android:textAppearanceSmall"
                android:text="don't have an account? REGISTER here"
                android:id="@+id/toRegisterActivity"
                android:gravity="center"
                android:textColor="@android:color/white"
                android:padding="5dp"></TextView>

        </LinearLayout>
    </ScrollView>

</LinearLayout>

Файл MainActivity.java

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;

public class MainActivity extends AppCompatActivity {

    private EditText email, pass;
    private Button login_button;
    private TextView toRegisterActivity;
    private ProgressDialog progressDialog;

    private FirebaseAuth mAuth;

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

        email = findViewById(R.id.email_login);
        pass = findViewById(R.id.pass_login);
        login_button = findViewById(R.id.login_button);
        toRegisterActivity = findViewById(R.id.toRegisterActivity);
        progressDialog = new ProgressDialog(this);

        mAuth = FirebaseAuth.getInstance();

        toRegisterActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent registerIntent  = new Intent(MainActivity.this, RegistrationActivity.class);
                startActivity(registerIntent);
            }
        });

        login_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                String mEmail = email.getText().toString().trim();
                String mPass = pass.getText().toString().trim();

                if (TextUtils.isEmpty(mEmail)){
                    email.setError("Email required!");
                    return;
                }
                if (TextUtils.isEmpty(mPass)){
                    pass.setError("Password required!");
                    return;
                }
                else {
                    progressDialog.setTitle("Login in ...");
                    progressDialog.setMessage("please wait as we log you in.");
                    progressDialog.setCanceledOnTouchOutside(false);
                    progressDialog.show();
                    mAuth.signInWithEmailAndPassword(mEmail,mPass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {

                            if (task.isSuccessful()){
                                Toast.makeText(MainActivity.this, "Login Successful", Toast.LENGTH_SHORT).show();
                                Intent homeIntent = new Intent(MainActivity.this, HomeActivity.class);
                                homeIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK |Intent.FLAG_ACTIVITY_CLEAR_TASK);
                                startActivity(homeIntent);
                                finish();
                                progressDialog.dismiss();
                            }else {
                                String errorMsg = task.getException().toString();
                                Toast.makeText(MainActivity.this, "Login Failed, please try again."+ errorMsg, Toast.LENGTH_SHORT).show();
                                progressDialog.dismiss();
                            }



                 }
                });
            }
        }
    });
}
}

StackTrace

11-04 21:25:31.840 16416-16416/com.example.checkmydailyspend E/Zygote: MountEmulatedStorage()
11-04 21:25:31.840 16416-16416/com.example.checkmydailyspend E/Zygote: v2
11-04 21:25:31.840 16416-16416/com.example.checkmydailyspend E/SELinux: [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL
11-04 21:25:33.202 16416-16416/com.example.checkmydailyspend E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.checkmydailyspend, PID: 16416
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.checkmydailyspend/com.example.checkmydailyspend.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3160)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3275)
        at android.app.ActivityThread.access$1000(ActivityThread.java:218)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1744)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:145)
        at android.app.ActivityThread.main(ActivityThread.java:7007)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.checkmydailyspend.MainActivity.onCreate(MainActivity.java:43)
        at android.app.Activity.performCreate(Activity.java:6609)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1134)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3113)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3275) 
        at android.app.ActivityThread.access$1000(ActivityThread.java:218) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1744) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:145) 
        at android.app.ActivityThread.main(ActivityThread.java:7007) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)

Answer 1

Изменить setContentView(R.layout.activity_registration); на setContentView(R.layout.MainActivity);