尝试调用虚拟方法“空对象引用”

Question

每当我尝试使用 firebase auth 注册用户时，我的应用就会崩溃。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: 致命异常: 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)' 在空对象引用上 在 com.google.android.gms.internal.zzdvv.zzb（未知来源） 在 com.google.android.gms.internal.zzdwc.zzb（未知来源） 在 com.google.firebase.auth.FirebaseAuth.signInWithEmailAndPassword（未知来源） 在 com.finalyearproject.vimelraj.qfoody.MainActivity.startSignIn(MainActivity.java:91) 在 com.finalyearproject.vimelraj.qfoody.MainActivity.access$000(MainActivity.java:23) 在 com.finalyearproject.vimelraj.qfoody.MainActivity$2.onClick(MainActivity.java:64) 在 android.view.View.performClick(View.java:5637) 在 android.view.View$PerformClick.run(View.java:22429) 在 android.os.Handler.handleCallback(Handler.java:751) 在 android.os.Handler.dispatchMessage(Handler.java:95) 在 android.os.Looper.loop(Looper.java:154) 在 android.app.ActivityThread.main(ActivityThread.java:6119) 在 java.lang.reflect.Method.invoke（本机方法） 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

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);

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);
                }

            }
        });
    }


}

Answer 2

以这种方式在 UI 线程上显示 Toast

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

            }
        });