在AngularJS重复部分功能调用多次 [英] Function Called Multiple Times in AngularJS Repeat Section

问题描述

我遇到，我想绑定到一个函数的输出NG重复循环中的一个问题。我发现功能正在每个项目两次而非一次是我期望调用。这里的NG-重复部分（注意在最后的calcRowTotal（）调用）：

I'm running into an issue where I want to bind to the output of a function inside of an ng-repeat loop. I'm finding that the function is being called twice per item rather than once as I'd expect. Here's the ng-repeat section (notice the calcRowTotal() call at the end):

<tr ng-repeat="row in timesheetRows">
    <td>
        <select ng-model="row.categoryID">
            <option ng-repeat="category in categories" value="{{category.id}}">
                {{category.title}}
            </option>
        </select>
    </td>
    <td ng-repeat="day in row.dayValues">
        <input type="text" ng-model="day.hours" />
    </td>
    <td>{{calcRowTotal($index, row)}}</td>
</tr>

该calcRowTotal（）函数图所示：

The calcRowTotal() function is shown next:

$scope.calcRowTotal = function (index, row) {
    console.log('calcRowTotal - Index: ' + index);
    var total = 0;
    for (var i = 0; i < row.dayValues.length; i++) {
        var num = parseFloat(row.dayValues[i].hours);
        if (isNaN(num)) {
            num = 0;
            //this.dayValues[i].hours = 0;
        }
        total += num;
    }
    //updateDayTotals();
    return total;
}

的项目之一的一个例子被迭代通过示出下一个：

An example of one of the items being iterated through is shown next:

{
    categoryID: 2,
    dayValues: [
                    { day: $scope.days[0], hours: 5 },
                    { day: $scope.days[1], hours: 0 },
                    { day: $scope.days[2], hours: 3 },
                    { day: $scope.days[3], hours: 0 },
                    { day: $scope.days[4], hours: 2 },
                    { day: $scope.days[5], hours: 5 },
                    { day: $scope.days[6], hours: 8 }
    ]
}

我看到在控制台下面（两项是我目前通过循环集合中）：

I'm seeing the following in the console (two items are currently in the collection I'm looping through):

calcRowTotal - Index: 0 
calcRowTotal - Index: 1 
calcRowTotal - Index: 0 
calcRowTotal - Index: 1 

我当然可以做一个rowTotal属性，但将preFER结合上面所显示的功能提供实时的数据。希望复制是一些简单的我失踪，所以我AP preciate任何反馈为什么我看到的重复。作为一个方面说明，如在文本框变化的一个数据，我需要更新的行总数，以及因此它可能是我需要一个不同的方法。有兴趣了解首先这种特定的情况虽然....绝对不想重复，因为可能有很多行可能。

I could certainly make a "rowTotal" property but would prefer to bind to "live" data provided by the function shown above. Hopefully the duplication is something simple I'm missing so I appreciate any feedback on why I'm seeing the duplication. As a side note, as data in one of the textboxes changes I need to update the row totals as well so it may be I need a different approach. Interested in understanding this particular situation first though....definitely don't want the duplication because there could be a lot of rows potentially.

下面是一个例子： http://jsfiddle.net/dwahlin/Y7XbY/2/

推荐答案

这是因为你绑定到一个函数前pression这里：

It's because you're binding to a function expression here:

<td>{{calcRowTotal($index, row)}}</td>

什么是它迫使该功能将每个项目的重新评估，在每个摘要。你会想要做的prevent是pre-计算该值并把它放在你的数组中开始。

What that does it force that function to be reevaluated on every item, on every digest. What you'll want to do to prevent that is pre-calculate that value and put it in your array to begin with.

做到这一点的方法之一就是建立阵列上的手表：

One way to do that is to set up a watch on your array:

$scope.$watch('timesheetRows', function(rows) {
   for(var i = 0; i < value.length; i++) {
     var row = rows[i];
     row.rowTotal = $scope.calcRowTotal(row, i);
   }
}, true);

然后，所有你所要做的就是绑定到新的值：

Then all you have to do is bind to that new value:

<td>{{row.rowTotal}}</td>

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