Question

我有.setOnClickListener按钮的问题。

每次我单击应用程序崩溃时都会遇到问题的按钮。

错误：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.xxx.uberclone.DriverLoginActivity.onCreate(DriverLoginActivity.java:75)

这是一段Java代码：

DriverLoginActivity.java：

package com.example.xxx.uberclone;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
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;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class DriverLoginActivity extends AppCompatActivity {

    private Button mLogin, mRegistration;
    private EditText mEmail, mPassword;

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener firebaseAuthListener;

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

        mAuth = FirebaseAuth.getInstance();

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

        mEmail = (EditText) findViewById(R.id.email);
        mPassword = (EditText) findViewById(R.id.password);

        mLogin = (Button) findViewById(R.id.driver);
        mRegistration = (Button) findViewById(R.id.registration);

        mRegistration.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final String email = mEmail.getText().toString();
                final String password = mPassword.getText().toString();
                mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(DriverLoginActivity.this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (!task.isSuccessful()){
                            Toast.makeText(DriverLoginActivity.this, "Sing-up error", Toast.LENGTH_SHORT).show();
                        }else{
                            String user_id = mAuth.getCurrentUser().getUid();
                            DatabaseReference current_user_db = FirebaseDatabase.getInstance().getReference().child("Users").child("Drivers");
                            current_user_db.setValue(true);
                        }
                    }
                });

            }
        });

        mLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final String email = mEmail.getText().toString();
                final String password = mPassword.getText().toString();
                mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(DriverLoginActivity.this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (!task.isSuccessful()) {
                            Toast.makeText(DriverLoginActivity.this, "Sing-up error", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
            }
        });


    }

    @Override
    protected void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(firebaseAuthListener);
    }

    @Override
    protected void onStop() {
        super.onStop();
        mAuth.removeAuthStateListener(firebaseAuthListener);
    }
}

下面是带有按钮的XML文件：

<?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=".MainActivity"
    android:orientation="vertical">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="I'm a driver"
        android:id="@+id/driver"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="I'm a costumer"
        android:id="@+id/customer"/>

</LinearLayout>

这是驱动程序XML代码：

<?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=".DriverLoginActivity"
    android:orientation="vertical">


    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="E-mail"
        android:id="@+id/email"/>
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Password"
        android:id="@+id/password"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Login"
        android:id="@+id/login"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Registration"
        android:id="@+id/registration"/>

</LinearLayout>

错误指向此行：

mLogin.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        final String email = mEmail.getText().toString();
        final String password = mPassword.getText().toString();
        mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(CustomerLoginActivity.this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if(!task.isSuccessful()){
                    Toast.makeText(CustomerLoginActivity.this, "sign in error", Toast.LENGTH_SHORT).show();
                }
            }
        });

    }
});

Answer 1

您的XML中没有ID为Button的{{1}}，只有R.id.registration和@+id/driver，因此将@+id/customer更改为R.id.registration用Java代码编写。

Android：.setOnClickListener上的java.lang.NullPointerException

1 个答案: