java-从具有全局变量的内部函数中获取空字符串

请帮我一点问题,我确定你可以做到：D

我正在尝试在Firestore文档“ user_cases_information”上使用字段“ case_number”设置一个字段

>首先,我声明这个全局变量

私有字符串case_number_consecutive = new String(“”);

>在.setonClickListener中,我有以下内容：(从其他文档中读取旧的连续编号或案例编号)

if (service_type.equals("support")){
    DocumentReference docRef = firestore_popup.collection("param_data_app").document("support_case_numbers");
    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
     @Override
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                 DocumentSnapshot document = task.getResult();
                 String consecutive = document.get("consecutive").toString();
                    if (consecutive.equals(null)) {
                         int random = new Random().nextInt(117) + 4;
                         case_number_consecutive = "IOC-09"+random;
                    } else {
                        case_number_consecutive = consecutive;                                        UpdateCaseNumbersConsecutive("support");
                    }
             } else {
                  int random = new Random().nextInt(117) + 4;
                  case_number_consecutive = "IOC-09"+random;
              }
      }
     });
} 


Map<String, Object> user_cases_information = new HashMap<>();
user_cases_information.put("case_number", case_number_consecutive);
... (then i use a firestore reference to put the new case number)

它假定当我检查Firestore时,恰好是我设置“ user_cases_information”文档的文档时,我应该看到数字或新的case_number,但是我总是得到空引用,连续的字段始终为null

为什么我得到这个空值？我用烤面包,然后放在它之前：

Toast.makeText(...."Value: "+case_number_consecutive
Map<String, Object> user_cases_information = new HashMap<>();
user_cases_information.put("case_number", case_number_consecutive);

并且它显示为null,因此上述函数中的值或数据丢失

我怎样才能解决这个问题？？？非常感谢.

解决方法:

这样做的原因是因为firebase正在异步执行,并且您正在编码,就像一切都同步发生一样.这是什么意思？这意味着firebase调用不会立即从服务器返回一个值,需要花费一些时间来获取该值,但是其余代码在响应返回之前正在执行,因此这就是问题所在.因此,即使执行以下代码：

if (service_type.equals("support")){
    DocumentReference docRef = firestore_popup.collection("param_data_app").document("support_case_numbers");
    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
     @Override
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                 DocumentSnapshot document = task.getResult();
                 String consecutive = document.get("consecutive").toString();
                    if (consecutive.equals(null)) {
                         int random = new Random().nextInt(117) + 4;
                         case_number_consecutive = "IOC-09"+random;
                    } else {
                        case_number_consecutive = consecutive;                                        UpdateCaseNumbersConsecutive("support");
                    }
             } else {
                  int random = new Random().nextInt(117) + 4;
                  case_number_consecutive = "IOC-09"+random;
              }
      }
     });
}

等到响应返回时,您的其他代码：

Map<String, Object> user_cases_information = new HashMap<>();
user_cases_information.put("case_number", case_number_consecutive);

已经完成并被调用,那么您将永远无法从firebase获得实际值.

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您可以执行以下操作：

interface Callback{
        void firebaseResponseCallback(String result);//whatever your return type is.
    }

更改此方法的签名,如下所示：

public void getCaseNumber(Callback callback) {

将您的代码更改为此：

if (service_type.equals("support")){
    DocumentReference docRef = firestore_popup.collection("param_data_app").document("support_case_numbers");
    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
     @Override
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                 DocumentSnapshot document = task.getResult();
                 String consecutive = document.get("consecutive").toString();
                    if (consecutive.equals(null)) {
                         int random = new Random().nextInt(117) + 4;
                         case_number_consecutive = "IOC-09"+random;
                    } else {
                        case_number_consecutive = consecutive;                                        UpdateCaseNumbersConsecutive("support");
                    }
             } else {
                  int random = new Random().nextInt(117) + 4;
                  case_number_consecutive = "IOC-09"+random;
              }

       callback.firebaseResponseCallback(case_number_consecutive);
      }
     });
}

然后,当您调用getCaseNumber时：

getCaseNumber(new Callback() {
        @Override
        public void firebaseResponseCallback(String result) {
            here, this result parameter that comes through is your api call result to use, so result will be your case number, so make your objects inside this method, not outside
        }
    });
}

编辑

我专门针对这些类型的问题发布了这篇文章：
How to get data from any asynchronous operation in android

java-从具有全局变量的内部函数中获取空字符串

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