android - 尝试调用虚拟方法 'null object reference'

Question

每当我尝试使用 firebase auth 注册用户时，我的应用程序就会崩溃。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();
                    }

                }
            });
        }


    }
}

这是我的日志:

08-03 05:50:41.766 17746-17746/com.finalyearproject.vimelraj.qfoody E/AndroidRuntime: FATAL EXCEPTION: main Process: com.finalyearproject.vimelraj.qfoody, PID: 17746 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.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$2.onClick(MainActivity.java:64) at android.view.View.performClick(View.java:5637) at android.view.View$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)

Answer 1

在 onComplete 方法中使用下面的代码。

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

更新

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);
                }

            }
        });
    }


}