java - 为什么这个 toast 在不应该出现的时候出现了？

Question

你好

我有一种方法可以验证数据库中是否已存在电话号码或电子邮件，如果是，用户将收到一个提示，表示其已注册，并将返回到注册 Activity ，如果不存在，它将继续使用代码,

public class VerficatePhone extends AppCompatActivity {
private String mVerficationId,phoneNumber,sentCode;
private User user;
private EditText phoneCodeEditText;
private PhoneAuthProvider.ForceResendingToken mResend;
private Button activate;
private TextView backToSignupText;
private ProgressBar pBar;
private FirebaseAuth mAuth;
private DatabaseReference reff;
private boolean executed =false;



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

    phoneCodeEditText=findViewById(R.id.verificationEditText);
    activate=findViewById(R.id.activate);
    backToSignupText=findViewById(R.id.backToSignupText);
    pBar=findViewById(R.id.progressBar);

    mAuth=FirebaseAuth.getInstance();
    reff= FirebaseDatabase.getInstance().getReference().child("User");


    //getting the user that has been sent from the sign up Activity and the phone number
    if(getIntent().getSerializableExtra("userFromSignUp")!=null)
    {
        user=(User)getIntent().getSerializableExtra("userFromSignUp");
        phoneNumber=user.getPhoneNumber();

    }
    else
    {
        phoneNumber="000";
        Toast.makeText(this,"Error",Toast.LENGTH_SHORT).show();
    }

    if(!executed)
    {
        checkPhoneNumIfExists(user);
        executed =true;
    }

    sendCode(phoneNumber);
}

我的 checkPhoneNumIfExists 方法是这样的

 private void checkPhoneNumIfExists (final User currentUser)
{
    Log.i("checkPhoneNumIfExists method","processing");
     FirebaseDatabase fDb=FirebaseDatabase.getInstance();
        DatabaseReference dbRef=fDb.getReference();
        dbRef.child("User").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                Iterable<DataSnapshot> children=dataSnapshot.getChildren();
                for(DataSnapshot child:children)
                {
                    if(currentUser!=null && child!=null)
                    {
                        User user= child.getValue(User.class);
                        if(user!=null && !user.getPhoneNumber().isEmpty())
                        {
                            if(currentUser.getPhoneNumber().equals(user.getPhoneNumber()) || currentUser.geteMail().equals(user.geteMail()))
                            {
                                Toast.makeText(VerficatePhone.this,"already registred",Toast.LENGTH_SHORT).show();
                                Intent i =new Intent(VerficatePhone.this,signUpActivity.class);
                                i.putExtra("userFromVerificate",currentUser);
                                i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                                startActivity(i);
                                finish();



                            }
                        }

                    }
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

    executed =true;

}

所以这就是问题所在，当用户未注册时，它会继续执行代码并在 onCreate 方法中执行 sendCode 方法，这将打开一个新 Activity ，但每当从 sendCode 方法打开新 Activity 时， checkPhoneNumIfExists 方法的 toast它出现了。

那为什么会发生这种情况？

Answer 1

onDataChange() 是一个异步回调。任何依赖它的数据或函数都应该从回调中访问或触发。

由于您似乎不打算每次都运行数据库检查，因此我建议您在离开并返回 Activity 时查看 SharedPreferences 以保留该变量。您可以在执行 onDataChange() 时存储 executed 的值，并在 if 语句之前的 onCreate() 中检索该值。

@Override
protected void onCreate(Bundle savedInstanceState){
    // ...

    // If you're using SharedPreferences, retrieve the value here

    if(!executed){
        checkDb(user)
    }else{
        // I'm assuming you only want to send the code when executed is true
        // which means that, for this approach, you should call sendCode()
        // again inside of your onDataChange()
        sendCode(phoneNum);
    }
}

private void checkDb(final User currentUser){
    // ...

    myRef.addValueEventListener(new ValueEventListener(){
        @Override
        public void onDataChange(DataSnapshot dataSnapshot){
            for(DataSnapshot snap: dataSnapshot.getChildren()){
                // do something with the data
                // ...
            }

            // This is where you can set the value of a variable 
            // or execute a function that relies upon the data of the callback. 

            // If you're using SharedPreferences, you would store the value here.

            // You may want to call sendCode() again here
        }
    });
}

您可以通过访问 https://developer.android.com/training/data-storage/shared-preferences 了解 SharedPreferences