如何正确订阅更改？ -Angularfire2 [英] How do I properly subscribe to changes? -Angularfire2

问题描述

您好，我没有经常使用Firebase。我用来获取值的方法感觉很乱......



我正在使用这种方法来获取每个object.value的总和金额一个ListObservable



谁能说出订阅更改的最佳方式是什么，以便totalAmount保持最新状态？

Hello, I haven't used Firebase a lot. The method I'm using to get values feels messy...

I'm using this method to get the sum amount for each object.value in a ListObservable

Can anyone tell what would be the best way to subscribe to changes such that the totalAmount stays up to date?

//Returns a promise of the total sum for each object.amount under a category
getTotalAmountPromise(observable) {
  let totalAmount: number = 0;
  return new Promise(function(resolve, reject) {
    let count = 0;

    observable.$ref.ref.on('child_added', childs => {
      childs.ref.once('value', obj => {
        totalAmount += obj.val().amount;
        count++;

        let length = childs.numChildren();
        if(count == length) {
          resolve(totalAmount);
        }
      });
      setTimeout(() => {
        if (!(count == length))
          reject(Error('Data rejected. Count: ' + count + ', Childs: ' + length));

      }, 5000);
    });

  });
}

我尝试过：



我似乎无法找到一个好办法。希望这里有人可以提供一些指导。

What I have tried:

I can't seem to find a good way to do this. Was hoping anyone here could come with some guidance.

推荐答案

ref.ref.on（' child_added'，childs => {
childs.ref.once（' value'，obj => {
totalAmount + = obj.val（）。amount;
count ++;

让 length = childs.numChildren（）;
if （count == length）{
resolve （totalAmount）;
}
}）;
setTimeout（（）=> {
if （！（ count == length））
reject（错误（' 数据被拒绝。计数：' + count + ' ，Childs：' + length））;

}， 5000 ）;
}）;

}）;
}

ref.ref.on('child_added', childs => { childs.ref.once('value', obj => { totalAmount += obj.val().amount; count++; let length = childs.numChildren(); if(count == length) { resolve(totalAmount); } }); setTimeout(() => { if (!(count == length)) reject(Error('Data rejected. Count: ' + count + ', Childs: ' + length)); }, 5000); }); }); }

我尝试过：



我似乎无法找到一个好办法。希望这里有人可以提供一些指导。

What I have tried:

I can't seem to find a good way to do this. Was hoping anyone here could come with some guidance.

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