Firebase 在Firestore中创建具有电子邮件和密码的用户时，如何从OnCompleteListener返回值？

我要写的代码是

private String val;
    public String checkEmail(){

        FirebaseFirestore db = FirebaseFirestore.getInstance();
        db.collection("cities").whereEqualTo("cities", "Boston").get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()){
                            val = "City exists";
                        }else{
                            val = "City does not exist";
                        }
                    }
                });
        return val;
    }

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此代码将val返回为null，而不是值。如何解决此问题？

我确信这是因为调用是异步的，请将方法更改为non-return value void，并创建一个接口回调，以便在调用完成时返回值。试试这个

interface CityCallback {
     void isCityExist(boolean exist);
}

public void checkEmail(CityCallback cityCallback){
    FirebaseFirestore db = FirebaseFirestore.getInstance();
    db.collection("cities").whereEqualTo("cities", "Boston").get()
            .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                @Override
                public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if (task.isSuccessful()){
                        cityCallback.isCityExist(true);
                    }else{
                        cityCallback.isCityExist(false);
                    }
                }
            });
}

---

我希望它能帮助您

我确信这一点，因为调用是异步的，请将您的方法更改为non-return value void，并创建一个接口回调，以便在调用完成时返回值。试试这个

interface CityCallback {
     void isCityExist(boolean exist);
}

public void checkEmail(CityCallback cityCallback){
    FirebaseFirestore db = FirebaseFirestore.getInstance();
    db.collection("cities").whereEqualTo("cities", "Boston").get()
            .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                @Override
                public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if (task.isSuccessful()){
                        cityCallback.isCityExist(true);
                    }else{
                        cityCallback.isCityExist(false);
                    }
                }
            });
}

我希望它能帮助你