如何修复显示 NullException 的错误，但我已经初始化了按钮的对象

Question

我遇到了这个错误，说 NullException，但我已经初始化了我的对象，但它仍然显示 null 异常。 怎么解决的，我反复查看程序，也设置了断点，但没有结果

代码：

package com.rishavgmail.coder.carescountrysactionresourcesexigencyservices;

import android.arch.core.executor.TaskExecutor;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TextInputLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.gms.tasks.TaskExecutors;
import com.google.firebase.FirebaseException;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.PhoneAuthCredential;
import com.google.firebase.auth.PhoneAuthProvider;

import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class VerifyPhone extends AppCompatActivity {
    private CoordinatorLayout coordinatorLayoutVerifyPhone;
    private TextInputLayout textInputLayoutOTP;
    private Button btnVerifyOTP;
    private String verificationID;
    private FirebaseAuth mAuth;
    private ProgressBar progressBarVerifyPhone;
    private String phoneNumber;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mAuth = FirebaseAuth.getInstance();
        String phoneNumber = getIntent().getStringExtra("phoneNumber");
        Initialization();
        sendVerificationCode(phoneNumber);
        btnVerifyOTP = findViewById(R.id.btnVerifyOTP);
        btnVerifyOTP.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String code = textInputLayoutOTP.getEditText().getText().toString().trim();
                if (code.isEmpty())
                {
                    textInputLayoutOTP.setError("Enter OTP");
                    return;
                }
                else if (code.length()<6)
                {
                    textInputLayoutOTP.setError("Enter OTP");
                    return;
                }
                progressBarVerifyPhone.setVisibility(View.VISIBLE);
                verifyCode(code);
            }
        });
    }
    private void verifyCode(String code)
    {
        PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationID,code);
        ProceedToRegister(credential);
    }
    private void ProceedToRegister(PhoneAuthCredential credential)
    {
        mAuth.signInWithCredential(credential)
        .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful())
                {
                    Intent intent=new Intent(VerifyPhone.this,AuthorityRegistration.class);
                    String AuthPhone = textInputLayoutOTP.getEditText().getText().toString().trim();
                    intent.putExtra("AuthPhone",AuthPhone);
                    startActivity(intent);
                }
                else
                {
                    Snackbar snackbar = Snackbar.make(coordinatorLayoutVerifyPhone,"Something went wrong !!",Snackbar.LENGTH_SHORT);
                    snackbar.show();
                }
            }
        });
    }
    private void Initialization()
    {
        progressBarVerifyPhone = findViewById(R.id.progressBarVerifyPhone);
        textInputLayoutOTP = findViewById(R.id.textInputLayoutVerifyOTP);
        coordinatorLayoutVerifyPhone = findViewById(R.id.coordinatorLayoutVerifyPhone);
    }
    private void sendVerificationCode(String number)
    {
        PhoneAuthProvider.getInstance().verifyPhoneNumber(number,60,TimeUnit.SECONDS, TaskExecutors.MAIN_THREAD,mCallBack);
    }
    private PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallBack =
            new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
                @Override
                public void onCodeSent(String s, PhoneAuthProvider.ForceResendingToken forceResendingToken) {
                    super.onCodeSent(s, forceResendingToken);

                    verificationID = s;
                }

                @Override
                public void onVerificationCompleted(PhoneAuthCredential phoneAuthCredential) {

                    String code = phoneAuthCredential.getSmsCode();
                    if (code!=null)
                    {
                        progressBarVerifyPhone.setVisibility(View.VISIBLE);
                        verifyCode(code);
                    }
                }

                @Override
                public void onVerificationFailed(FirebaseException e) {
                    Snackbar snackbar = Snackbar.make(coordinatorLayoutVerifyPhone,"Verification Failed !!",Snackbar.LENGTH_SHORT);
                    snackbar.show();
                }
            };
}

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.rishavgmail.coder.carescountrysactionresourcesexigencyservices.VerifyPhone.onCreate(VerifyPhone.java:44)

它正在从 Firebase 发送 OTP，但没有启动 VerifyOTP 活动进行验证

Answer 1

关键线是这些。

btnVerifyOTP = findViewById(R.id.btnVerifyOTP);
btnVerifyOTP.setOnClickListener(new View.OnClickListener() { 
...

错误消息说 NPE 被抛出是因为你在 null 上调用 setOnClickListener。这意味着btnVerifyOTP 是null。这反过来意味着findViewById(R.id.btnVerifyOTP) 正在返回null。

那为什么会这样呢？

一个可能的原因是您在调用setContentView 之前调用了findViewById；见findViewById returns null。事实上，正如其他人所指出的，你根本不打电话给setContentView。

假设这是问题所在，解决方法是在代码前面添加一个 setContentView 调用；例如在你的Initialization 方法被调用之前......因为你也在使用findViewById！

---

^{请更正方法名称中的样式错误。在 Java 中，方法名称应以 小写 字母开头。}

Answer 2

您忘记设置布局

setContentView(R.layout.your_layout);