Question

我正在使用一个应用程序，最初有一个介绍屏幕，只有在第一次启动应用程序时才会运行。在最后一张幻灯片中，我有两个按钮，即signInAsCustomer和signInAsSeller。两个意图都会带您进行相同的活动，但会传递两个不同的意图附加内容。 signInAsCustomer传递额外的密钥＆＃34;类型＆＃34;和价值＆＃34;客户＆＃34;而signInAsSeler传递额外的密钥＆＃34;类型＆＃34;和价值＆＃34;卖方＆＃34; 。当第二个活动开始时，我得到额外的，并根据额外的，我在特定的文本视图中设置一些文本。 SignInActivity的代码如下。

SignInActivity

private String type;
private TextView tv_seller_or_customer , forgot_password , guest_login ;
private EditText email , password ;
private Button login , signUp;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthStateListener;

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

    // Initialising Firebase Auth Object
    mAuth = FirebaseAuth.getInstance();

    // This is the Auth state listener .  It checks if the user is aldready signed In or not
    mAuthStateListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user != null)
            {
                // User is signed in
                // Goes to a new activity
                Intent i = new Intent(SignInActivity.this , MainActivity.class);
                startActivity(i);
            }else
            {
                // User is signed out
                // Shows sign in page to the user
                signInUser();
            }
        }
    };


}

@Override
protected void onResume() {
    super.onResume();
    mAuth.addAuthStateListener(mAuthStateListener);
}

@Override
protected void onPause() {
    super.onPause();
    if (mAuthStateListener != null)
    {
        mAuth.removeAuthStateListener(mAuthStateListener);
    }
}

public void signInUser()
{
    // This method initialises all the views in the signInPage
    initialiseViews();
    // Getting the intent extras and changing the activity depending upon the button pressed in the Intro Slider
   Intent i = getIntent();
    if (i != null) {
        type = i.getStringExtra("type");
        if (type.equals("seller")) {
            tv_seller_or_customer.setText("Seller");
            initialiseViews();
            guest_login.setVisibility(View.GONE);
        } else {
            tv_seller_or_customer.setText("Customer");
            initialiseViews();
        }
    }else
    {
        tv_seller_or_customer.setVisibility(View.GONE);
    }

    // Listener for loging in 
    login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            String emailString = email.getText().toString();
            String passwordString = password.getText().toString().trim();
            if (!Is_Valid_Email(emailString))
            {
                Toast.makeText(SignInActivity.this , "Please enter a valid Email ID", Toast.LENGTH_SHORT).show();
            }else {
                loginUser(emailString , passwordString);
            }
        }
    });

}

public boolean Is_Valid_Email(String email_check) {
    return !email_check.isEmpty() && isEmailValid(email_check);
}

boolean isEmailValid(CharSequence email) {
    return android.util.Patterns.EMAIL_ADDRESS.matcher(email)
            .matches();
}

public void loginUser(String emailLogin , String passwordLogin)
{
    mAuth.signInWithEmailAndPassword(emailLogin , passwordLogin)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (!task.isSuccessful())
                    {
                        Log.w("sign in", "Failed" , task.getException());
                    }else
                    {
                        Intent i = new Intent(SignInActivity.this , MainActivity.class);
                        startActivity(i);
                    }

                }
            });

}

public void initialiseViews()
{
   forgot_password = (TextView) findViewById(R.id.forgotPassword);
    guest_login = (TextView) findViewById(R.id.guest_tv);
    email = (EditText) findViewById(R.id.email_edt);
    password = (EditText) findViewById(R.id.pass_edt);
    login = (Button) findViewById(R.id.login_button);
    signUp = (Button) findViewById(R.id.sign_up_btn);
}}

我得到的错误

    E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.ankit_pc.pharmahouse, PID: 15750
              java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                  at com.example.ankit_pc.pharmahouse.SignInActivity.signInUser(SignInActivity.java:78)
                  at com.example.ankit_pc.pharmahouse.SignInActivity$1.onAuthStateChanged(SignInActivity.java:48)
                  at com.google.firebase.auth.FirebaseAuth$1.run(Unknown Source)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:7325)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) Application terminated.

我哪里出错？

Answer 1

您似乎忘记了初始化tv_seller_or_customer。只需将其添加到您的initialiseViews()函数中，您就应该好了。

e.g：

tv_seller_or_customer = (TextView) findViewById(R.id.tv_seller_or_customer)

Answer 2

在initialiseViews()中，您没有初始化tv_seller_or_customer，因此它会抛出NullPointerException。

Intialise tv_seller_or_customer，它会正常工作。

Answer 3

在oncreate of activity中调用initialiseViews（）。不需要调用其他方法只需在活动中的oncreate方法中调用一次。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sign_in);
initialiseViews();
///other code
}

使用Intent Extras时出错

3 个答案: