Android - NullPointerException 尝试调用虚拟方法 'com.google.android.gms.tasks.Task答案

【问题标题】：Android - NullPointerException Attempt to invoke virtual method 'com.google.android.gms.tasks.TaskAndroid - NullPointerException 尝试调用虚拟方法 'com.google.android.gms.tasks.Task
【发布时间】：2018-08-11 07:22:53
【问题描述】：

尝试设置一个使用 Firebase 身份验证来处理用户注册/登录的简单应用。这个问题非常令人困惑，因为我的物理测试设备（HTC M8 7.1.1）和模拟器（5P 7.1.1）的结果不同。

在模拟器上，单击登录或注册按钮时出现以下错误。

                                                                --------- beginning of crash
03-02 03:24:20.625 3002-3002/com.mad.losesano E/AndroidRuntime: FATAL EXCEPTION: main
                                                                Process: com.mad.losesano, PID: 3002
                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.tasks.Task com.google.android.gms.common.api.GoogleApi.zzb(com.google.android.gms.common.api.internal.zzdd)' on a null object reference
                                                                    at com.google.android.gms.internal.zzdvv.zzb(Unknown Source)
                                                                    at com.google.android.gms.internal.zzdwc.zzb(Unknown Source)
                                                                    at com.google.firebase.auth.FirebaseAuth.signInWithEmailAndPassword(Unknown Source)
                                                                    at com.mad.losesano.LoginActivity.userLogin(LoginActivity.java:69)
                                                                    at com.mad.losesano.LoginActivity.onClick(LoginActivity.java:105)
                                                                    at android.view.View.performClick(View.java:5637)
                                                                    at android.view.View$PerformClick.run(View.java:22429)
                                                                    at android.os.Handler.handleCallback(Handler.java:751)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                    at android.os.Looper.loop(Looper.java:154)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

在我的物理设备上，当我注册用户时，它按预期工作。用户帐户可以在 firebase 控制台中看到。当我在此设备上单击“登录”时，没有任何反应。似乎它甚至没有进入 OnClick 方法（通过在 OnClick 方法中运行 Log.d 消息进行测试，当我单击按钮时它不显示）。

这是登录活动代码

package com.mad.losesano;

        import android.app.Activity;
        import android.content.Intent;
        import android.support.annotation.NonNull;
        import android.os.Bundle;
        import android.util.Log;
        import android.util.Patterns;
        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;

public class LoginActivity extends Activity implements View.OnClickListener {

    FirebaseAuth mAuth;
    EditText et_email, et_password;
    Button login_button;

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

        mAuth = FirebaseAuth.getInstance();

        et_email = (EditText) findViewById(R.id.email_et_login);
        et_password = (EditText) findViewById(R.id.password_et_login);

        findViewById(R.id.register_tv).setOnClickListener(this);
        login_button = (Button) findViewById(R.id.login_button);
        login_button.setOnClickListener(this);

    }

    private void userLogin() {
        String email = et_email.getText().toString().trim();
        String password = et_password.getText().toString().trim();

        if (email.isEmpty()) {
            et_email.setError("Email is required");
            et_email.requestFocus();
            return;
        }

        if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            et_email.setError("Please enter a valid email");
            et_email.requestFocus();
            return;
        }

        if (password.isEmpty()) {
            et_password.setError("Password is required");
            et_password.requestFocus();
            return;
        }

        if (password.length() < 6) {
            et_password.setError("Minimum lenght of password should be 6");
            et_password.requestFocus();
            return;
        }

        mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(LoginActivity.this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    finish();
                    Intent intent = new Intent(LoginActivity.this, LoggedInActivity.class);
                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(intent);
                } else {
                    Toast.makeText(getApplicationContext(), task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();

        if (mAuth.getCurrentUser() != null) {
            finish();
            startActivity(new Intent(this, LoggedInActivity.class));
        }
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.register_tv:
                finish();
                Log.d("LoSeSANO", "Register Button Clicked");
                startActivity(new Intent(LoginActivity.this, SignupActivity.class));
                break;

            case R.id.login_button:
                Log.d("LoSeSANO", "Login Button Clicked");
                userLogin();
                break;
        }
    }
}

这是 SignupActivity 代码

package com.mad.losesano;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.util.Log;
import android.util.Patterns;
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.FirebaseAuthUserCollisionException;

/**
 * Created by oshau on 01/03/2018.
 */

public class SignupActivity extends Activity implements View.OnClickListener {

    EditText et_email, et_password;
    Button register_button;
    private FirebaseAuth mAuth;

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

        et_email = (EditText) findViewById(R.id.email_et_login);
        et_password = (EditText) findViewById(R.id.password_et_login);

        mAuth = FirebaseAuth.getInstance();

        register_button = (Button) findViewById(R.id.register_button);
        register_button.setOnClickListener(this);
        findViewById(R.id.login_tv).setOnClickListener(this);

    }

    private void registerUser() {
        Log.d("LoSeSANO", "Email Address: " + et_email.getText().toString());
        String email = et_email.getText().toString().trim();
        String password = et_password.getText().toString().trim();

        if (email.isEmpty()) {
            et_email.setError("Email is required");
            et_email.requestFocus();
            return;
        }

        if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            et_email.setError("Please enter a valid email");
            et_email.requestFocus();
            return;
        }

        if (password.isEmpty()) {
            et_password.setError("Password is required");
            et_password.requestFocus();
            return;
        }

        if (password.length() < 6) {
            et_password.setError("Minimum lenght of password should be 6");
            et_password.requestFocus();
            return;
        }

        mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(SignupActivity.this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    finish();
                    startActivity(new Intent(SignupActivity.this, LoginActivity.class));
                } else {

                    if (task.getException() instanceof FirebaseAuthUserCollisionException) {
                        Toast.makeText(getApplicationContext(), "You are already registered", Toast.LENGTH_SHORT).show();

                    } else {
                        Toast.makeText(getApplicationContext(), task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                    }

                }
            }
        });

    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.register_button:
                registerUser();
                break;

            case R.id.login_tv:
                finish();
                startActivity(new Intent(SignupActivity.this, LoginActivity.class));
                break;
        }
    }
}

如果需要，这是我的 login_activity.xml 和 signup_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    >

    <TextView
        android:id="@+id/welcome_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif-light"
        android:text="@string/welcome_string"
        android:textColor="#f0eeec"
        android:textSize="40dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        tools:layout_editor_absoluteY="80dp" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="202dp"
        android:layout_height="62dp"
        android:layout_marginTop="8dp"
        android:fontFamily="sans-serif-light"
        android:gravity="center"
        android:text="@string/sub_welcome_string"
        android:textColor="#f0eeec"
        android:textSize="14dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/welcome_tv" />

    <EditText
        android:id="@+id/email_et_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:backgroundTint="@android:color/holo_green_light"
        android:ems="10"
        android:fontFamily="sans-serif-light"
        android:inputType="textPersonName"
        android:text="@string/register_et_string"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

    <EditText
        android:id="@+id/password_et_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:backgroundTint="@android:color/holo_green_light"
        android:ems="10"
        android:fontFamily="sans-serif-light"
        android:hint="Password"
        android:inputType="textPassword"
        android:text="Password"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/email_et_login" />

    <Button
        android:id="@+id/login_button"
        android:layout_width="151dp"
        android:layout_height="55dp"
        android:layout_marginTop="16dp"
        android:backgroundTint="#6c8c0e"
        android:fontFamily="sans-serif-light"
        android:text="@string/login_register_button_string"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/password_et_login" />

    <TextView
        android:id="@+id/register_tv"
        android:layout_width="wrap_content"
        android:layout_height="22dp"
        android:layout_marginTop="8dp"
        android:backgroundTint="#6c8c0e"
        android:fontFamily="sans-serif-light"
        android:text="@string/register_tv_string"
        android:textColor="#f0eeec"
        android:textSize="16dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/login_button" />

    <TextView
        android:id="@+id/password_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:backgroundTint="#6c8c0e"
        android:fontFamily="sans-serif-light"
        android:text="@string/forgot_password_tv_string"
        android:textColor="#f0eeec"
        android:textSize="16dp"
        app:layout_constraintHorizontal_bias="0.501"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/register_tv" />

</android.support.constraint.ConstraintLayout>

注册活动

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    >

    <TextView
        android:id="@+id/welcome_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif-light"
        android:text="@string/welcome_string"
        android:textColor="#f0eeec"
        android:textSize="40dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        tools:layout_editor_absoluteY="80dp" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="202dp"
        android:layout_height="62dp"
        android:layout_marginTop="8dp"
        android:fontFamily="sans-serif-light"
        android:gravity="center"
        android:text="@string/sub_welcome_string"
        android:textColor="#f0eeec"
        android:textSize="14dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/welcome_tv" />

    <EditText
        android:id="@+id/email_et_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:backgroundTint="@android:color/holo_green_light"
        android:ems="10"
        android:fontFamily="sans-serif-light"
        android:inputType="textPersonName"
        android:text="@string/register_et_string"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

    <EditText
        android:id="@+id/password_et_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:backgroundTint="@android:color/holo_green_light"
        android:ems="10"
        android:fontFamily="sans-serif-light"
        android:hint="Password"
        android:inputType="textPassword"
        android:text="Password"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/email_et_login" />

    <Button
        android:id="@+id/register_button"
        android:layout_width="151dp"
        android:layout_height="55dp"
        android:layout_marginTop="16dp"
        android:backgroundTint="#6c8c0e"
        android:fontFamily="sans-serif-light"
        android:text="@string/register_tv_string"
        android:textColor="#f0eeec"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/password_et_login" />

    <TextView
        android:id="@+id/login_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="12dp"
        android:backgroundTint="#6c8c0e"
        android:fontFamily="sans-serif-light"
        android:text="@string/login_register_button_string"
        android:textColor="#f0eeec"
        android:textSize="16dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/register_button" />

</android.support.constraint.ConstraintLayout>

任何帮助将不胜感激！

【问题讨论】：

模拟器上有播放服务吗？
查看相关问题的答案：stackoverflow.com/a/48975027/4815718
糟糕。我的愚蠢疏忽。更新了 GPS，它不再崩溃。但是，当我单击“登录”时，什么也没有发生（它应该打开 LoggedInActivity）。大概是什么傻事。非常感谢您的帮助！
What is a NullPointerException, and how do I fix it?的可能重复
@AbuYousuf 仅仅因为问题包含NullPointerException 这个词并不意味着它是重复某人询问 NPE 是什么。在这个问题中，他没有询问什么是 NPE，但是当他知道他正确填写了所有内容时，为什么他会得到它。并非所有 NPE 都是某人编码错误的结果（因为他的评论表明这与没有正确版本的 GPS 有关）

标签： android firebase nullpointerexception firebase-authentication

【解决方案1】：

这是 Bob Snyder 的解决方案： Android Firebase Auth Crash on KitKat

根据他的回答，我在启动活动的 onCreate() 方法中做了这个：

if (GoogleApiAvailability.getInstance().isGooglePlayServicesAvailable(this) == ConnectionResult.SUCCESS) {
    // OK, you can do your job
}

您还应该处理其他结果：SERVICE_MISSING、SERVICE_UPDATING、SERVICE_VERSION_UPDATE_REQUIRED、SERVICE_DISABLED、SERVICE_INVALID

【讨论】：

【解决方案2】：

我遇到了完全相同的问题（也使用了 firebase），并通过使用 genymotion 安装 gapps 解决了它。

【讨论】：

【解决方案3】：

我研究了这个问题，发现当手机没有任何谷歌帐户时会出现错误。

【讨论】：