如何解决此问题：尝试调用虚拟方法 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)

Question

我是在 Android studio 上创建移动应用程序的新手。 我收到一个错误，如下所示

Logcat展示

引起：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)'

在 comm.example.login_logout.Login.onCreate(Login.java:64)

// 我转到这条线，但我不知道。

当我运行应用程序时，它可以构建，但仍然崩溃。

我的xml文件：activity_login.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"
tools:context=".Login"
android:orientation="vertical"
android:gravity="center"
android:padding="15dp">

<!--Login-->
<TextView
    android:id="@+id/textview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="20dp"
    android:gravity="center"
    android:text="@string/login"
    android:textSize="25sp"
    android:textStyle="bold" />

<!--Email-->
<com.google.android.material.textfield.TextInputLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >
    <com.google.android.material.textfield.TextInputEditText
        android:id="@+id/email"
        android:hint="@string/email"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</com.google.android.material.textfield.TextInputLayout>

<!--Password-->
<com.google.android.material.textfield.TextInputLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >
    <com.google.android.material.textfield.TextInputEditText
        android:id="@+id/password"
        android:hint="@string/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</com.google.android.material.textfield.TextInputLayout>

<ProgressBar
    android:id="@+id/progressBar"
    android:visibility="gone"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

<!--Button-->
<Button
    android:id="@+id/btn_login"
    android:text="@string/login"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

<TextView
    android:textStyle="bold"
    android:textSize="15sp"
    android:gravity="center"
    android:layout_marginTop="20dp"
    android:id="@+id/registerNow"
    android:text="@string/click_to_register"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>
</LinearLayout>

Java 文件： Login.java

    package com.example.login_logout;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import com.example.login_logout.R.id;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

import java.util.concurrent.CountedCompleter;

public class Login extends AppCompatActivity {

TextInputEditText editTextEmail, editTextPassword;
Button buttonLogin;
FirebaseAuth mAuth;
ProgressBar progressBar;
TextView textView;

@Override
public void onStart() {
    super.onStart();
    // Check if user is signed in (non-null) and update UI accordingly.
    FirebaseUser currentUser = mAuth.getCurrentUser();
    if(currentUser != null){
        Intent intent = new Intent(getApplicationContext(), MainActivity.class);
        startActivity(intent);
        finish();
    }
}


@SuppressLint("MissingInflatedId")
@Override
protected  void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);


    mAuth = FirebaseAuth.getInstance();
    editTextEmail = findViewById(R.id.email);
    editTextPassword = findViewById(R.id.password);
    buttonLogin = findViewById(R.id.btn_login);
    progressBar = findViewById(R.id.progressBar);
    textView = findViewById(R.id.registerNow);
    textView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(getApplicationContext(), Register.class);
            startActivity(intent);
            //finish();
        }
    });

    buttonLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            progressBar.setVisibility(View.VISIBLE);
            String email,password;
            email = String.valueOf(editTextEmail.getText());
            password = String.valueOf(editTextPassword.getText());

            // check it empty or not
            if (TextUtils.isEmpty(email)) {
                Toast.makeText(Login.this,"Enter email", Toast.LENGTH_SHORT).show();
                return;
            }
            if (TextUtils.isEmpty(password)) {
                Toast.makeText(Login.this,"Enter password", Toast.LENGTH_SHORT).show();
                return;
            }

            mAuth.signInWithEmailAndPassword(email, password)
                    .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {
                            progressBar.setVisibility(View.GONE);
                            if (task.isSuccessful()) {
                                Toast.makeText(getApplicationContext(), "Login Successful",Toast.LENGTH_SHORT).show();
                                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                                startActivity(intent);
                                finish();
                            } else {
                                Toast.makeText(Login.this, "Authentication failed.",
                                        Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
        }
    });
}
}

如何解决这个问题？

Answer 1

很明显您在登录活动中使用“R.layout.activity_register”。正如您在问题中提到的那样，它应该是“R.layout.activity_login”