在Firebase中自动增加一个值 [英] Auto-increment a value in Firebase

问题描述

如何从Android客户端自动增加存储在Firebase中的值？目前：我声明 int id = 1 。当我增加，我看到值2，3等被存储。这很好，但是当我重新运行这个项目的时候， id 被设置为等于1。

它的行为像一个静态变量，所以我可以创建一个ID从1到无穷大而不需要重新设置。

$ b

UPDATED FAILED

我使用以下方法将Firebase引用和字符串传递给函数incrementCounter。

  if（language_chosen.equalsIgnoreCase（english））
 {
 Firebase publRef = f.child （ 语言）子（ 英语）子（ 信息）。; 
 Firebase newPublRef = publRef.push（）; 
 writeMsgActivity demo = new writeMsgActivity（）; 
 demo.incrementCounter（newPublRef，the_msg_enter）; 
 
 
 
 
 
 $ b现在我尝试在 public void incrementCounter（Firebase publref，String my_msg）在oncomplete方法，但它给了我一个错误。
 
 
 <$ c （）{$ c $> public void incrementCounter（Firebase publref，String my_msg）{
 publref.runTransaction（new Transaction.Handler（）{
 @Override 
 public Transaction.Result doTransaction（final MutableData currentData）{ $（））
 if（currentData.getValue（）== null）{
 currentData.setValue（1）; 
} else {
 currentData.setValue（（Long）currentData.getValue + 1）; 
} 
 
 return Transaction.success（currentData）; 
} 
 $ b $ public void onComplete（FirebaseError firebaseError，boolean committed，DataSnapshot currentData ）{
 if（firebaseError！= null）{
 System.out.println（Firebase计数器增量失败）; 
} else {
 System.out.println（Firebase counter incremented。）; 
 
 Map< String，Object> publ = new HashMap< String，Object>（）; 
 publ.put（pubMsg，my_msg）; 
 publ.put（id，currentData）; 
 publref.setValue（publ）; 
} 
} 
}）; 
 
 
 
 
 $ b 
 更新已解决 
 最终Firebase upvoteref = new Firebase（https://shareurday.firebaseio.com/Message/+ msg_id +/ upvotes）; 
 
 upvoteref.runTransaction（new Transaction.Handler（）{
 @Override 
 public Transaction.Result doTransaction（final MutableData currentData）{
 if（currentData.getValue ）== null）{
 currentData.setValue（1）; 
} else {
 currentData.setValue（（Long）currentData.getValue（）+ 1）; 
} 
 return Transaction.success（currentData）; 
} 
 
 public void onComplete（firebaseError firebaseError，boolean committed，DataSnapshot currentData）{
 if（firebaseError！= null）{ 
 System.out.println（Firebase计数器增量失败。）; 
} else {
 System.out.println（Firebase counter increment。）; 
} 
} 
 }）; 
  
变量msg_id是来自push的随机生成的id。 
 
下面是一个递增单个计数器的示例方法。关键的想法是，您要么创建条目（将其设置为1），要么对现有条目进行变异。在这里使用事务可以确保如果多个客户端同时尝试增加计数器，所有请求最终都会成功。从Firebase文档（重点是我的）：
 
 
 
 
使用我们的事务功能处理可能被并发更新损坏的复杂数据  
 
 
 
 
  public void incrementCounter（）{
 firebase.runTransaction new Transaction.Handler（）{
 @Override 
 public Transaction.Result doTransaction（final MutableData currentData）{
 if（currentData.getValue（）== null）{
 currentData。 setValue（1）; 
} else {
 currentData.setValue（（Long）currentData.getValue（）+ 1）; 
} 
 
 return Transaction.success currentData）; 
} 
 
 @Override 
 public void onComplete（firebaseError firebaseError，boolean committed，DataSnapshot currentData）{$ b $ if（firebaseError！= null）{
 Log.d（Firebase counter increm ent失败了。）; 
} else {
 Log.d（Firebase counter incremented。）; 
} 
} 
}）; 
} 
  
 
How do I auto increment a value stored in Firebase from an Android client?


Currently: I declare int id = 1. When I increment, I see the values 2, 3 etc. being stored. That's fine, but when I re-run the project, id is set equal to 1 again.

I want it to behave like a static variable, so I can create an id which will go from 1 to infinity without resetting.

UPDATED FAILED

I used the following to pass the Firebase reference and a string to the function incrementCounter. 
if(language_chosen.equalsIgnoreCase("english"))
 {
   Firebase publRef = f.child("Language").child("English").child("Message");
   Firebase newPublRef = publRef.push();
   writeMsgActivity demo = new writeMsgActivity();
   demo.incrementCounter(newPublRef,the_msg_enter);                                 
  }
Now I try to use the passed reference and string at   public void incrementCounter(Firebase publref,String my_msg) in the oncomplete method but it gives me an error.
   public void incrementCounter(Firebase publref,String my_msg) {
    publref.runTransaction(new Transaction.Handler() {
        @Override
        public Transaction.Result doTransaction(final MutableData currentData) {
            if (currentData.getValue() == null) {
                currentData.setValue(1);
            } else {
                currentData.setValue((Long) currentData.getValue() + 1);
            }

            return Transaction.success(currentData);
        }

        public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
            if (firebaseError != null) {
                System.out.println("Firebase counter increment failed.");
            } else {
                System.out.println("Firebase counter increment succeeded.");

                Map<String, Object> publ = new HashMap<String, Object>();
                publ.put("pubMsg", my_msg);
                publ.put("id",currentData);
                publref.setValue(publ);
            }
        }
    });
}
UPDATED SOLVED
                final Firebase upvoteref = new Firebase("https://shareurday.firebaseio.com/Message/"+msg_id+"/upvotes"); 

            upvoteref.runTransaction(new Transaction.Handler() {
                @Override
                public Transaction.Result doTransaction(final MutableData currentData) {
                    if (currentData.getValue() == null) {
                        currentData.setValue(1);
                    } else {
                        currentData.setValue((Long) currentData.getValue() + 1);
                    }
                    return Transaction.success(currentData);
                }

                public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
                    if (firebaseError != null) {
                        System.out.println("Firebase counter increment failed.");
                    } else {
                        System.out.println("Firebase counter increment succeeded.");
                    }
                }
            });
The variable msg_id is the random generated id from push.
解决方案
Here's an example method that increments a single counter. The key idea is that you are either creating the entry (setting it equal to 1) or mutating the existing entry. Using a transaction here ensures that if multiple clients attempt to increment the counter at the same time, all requests will eventually succeed. From the Firebase documentation (emphasis mine):

  
Use our transactions feature when working with complex data that could be corrupted by concurrent updates


public void incrementCounter() {
    firebase.runTransaction(new Transaction.Handler() {
        @Override
        public Transaction.Result doTransaction(final MutableData currentData) {
            if (currentData.getValue() == null) {
                currentData.setValue(1);
            } else {
                currentData.setValue((Long) currentData.getValue() + 1);
            }

            return Transaction.success(currentData);
        }

        @Override
        public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
            if (firebaseError != null) {
                Log.d("Firebase counter increment failed.");
            } else {
                Log.d("Firebase counter increment succeeded.");
            }
        }
    });
}


                        
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