尝试调用虚方法'null object reference'-Java 学习之路

每当我尝试使用firebase auth注册用户时，我的应用程序崩溃了 . 我的代码如下：

public class MainActivity extends AppCompatActivity {


   private EditText mEmailField;
   private EditText mPasswordField;

   private Button mLoginBtn;

   private FirebaseAuth mAuth;

   private FirebaseAuth.AuthStateListener mAuthListener;


    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mAuth = FirebaseAuth.getInstance();

        mEmailField = (EditText)findViewById(R.id.emailField);
        mPasswordField = (EditText)findViewById(R.id.passwordField);

        mLoginBtn = (Button)findViewById(R.id.buttonLogin);

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {

                if(firebaseAuth.getCurrentUser() != null) {

                    startActivity(new Intent(MainActivity.this, Home.class));

                }

            }
        };

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

                startSignIn();

            }
        });

    }

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

        mAuth.addAuthStateListener(mAuthListener);

    }

    private void startSignIn() {

        String email = mEmailField.getText().toString();
        String password = mPasswordField.getText().toString();

        if(TextUtils.isEmpty(email) || TextUtils.isEmpty(password)) {

            Toast.makeText(MainActivity.this, "Fields are empty", Toast.LENGTH_LONG).show();

        } else {

            mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {

                    if (!task.isSuccessful()) {

                        Toast.makeText(MainActivity.this, "Sign In Failed!!", Toast.LENGTH_LONG).show();
                    }

                }
            });
        }


    }
}

这是我的logcat：

08-03 05：50：41.766 17746-17746 / com.finalyearproject.vimelraj.qfoody E / AndroidRuntime：FATAL EXCEPTION：main进程：com.finalyearproject.vimelraj.qfoody，PID：17746 java.lang.NullPointerException：尝试调用虚拟方法'com.google.android.gms.tasks.Task com.google.android.gms.common.api.GoogleApi.zzb(com.google.android.gms.common.api.internal.zzdd）'上的null com.google.android.gms.internal.zzdvv.zzb（未知来源）中com.google.android.gms.internal.zzdwc.zzb（未知来源）的对象参考，位于com.google.firebase.auth.FirebaseAuth.signInWithEmailAndPassword （未知来源）com.finalyearproject.vimelraj.qfoody.MainActivity.startSignIn（MainActivity.java:91）at com.finalyearproject.vimelraj.qfoody.MainActivity.access $ 000（MainActivity.java:23）at com.finalyearproject.vimelraj . qfoody.MainActivity $ 2.onClick（MainActivity.java:64）在android.view.View.View.performClick（View.java:5637）android.view.View $ PerformClick.run（View.java:22429）在android.os上 . Handler.handleCallback（H andler.java:751）android.app.Handler.dispatchMessage（Handler.java:95）android.app.Looper.loop（Looper.java:154）android.app.ActivityThread.main（ActivityThread.java:6119））at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:886）的com.android.internal.os.ZygoteInit.main（ZygoteInit）中的java.lang.reflect.Method.invoke（Native Method）的.java：776）

2 回答

在 onComplete 方法中使用以下代码 .

new android.os.Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            Toast.makeText(MainActivity.this, "Sign In Failed!!", Toast.LENGTH_LONG).show();
        }
    }, 100);

update

private void startSignIn() {

    String email = mEmailField.getText().toString();
    String password = mPasswordField.getText().toString();

    if( email == null || password == null ||  TextUtils.isEmpty(email) || TextUtils.isEmpty(password)) {

        Toast.makeText(MainActivity.this, "Fields are empty", Toast.LENGTH_LONG).show();

    } else {

        mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {

                if (!task.isSuccessful()) {

                    new android.os.Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        Toast.makeText(MainActivity.this, "Sign In Failed!!", Toast.LENGTH_LONG).show();
    }
}, 100);
                }

            }
        });
    }


}

回复于 2024-04-27T07:21:29+08:00

以这种方式在UI上显示Toast

runOnUiThread(new Runnable() {
            @Override
            public void run() {
        Toast.makeText(MainActivity.this, "Sign In Failed!!", Toast.LENGTH_LONG).show();

            }
        });

回复于 2024-04-27T07:21:29+08:00

尝试调用虚方法'null object reference'

2 回答

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