Question

首先很抱歉提出这个非常常见的问题，但我无法解决此错误。我有一些null值的属性。该属性为json[i].outcome_status.category，目标是计算json结构中每个类别的出现次数，而不使用类别的null属性。我试图逃避它：

if(json[i].outcome_status.category != null)

但是，我仍然收到一个错误，即该属性为null。这是我的代码：

<!--Load the AJAX API-->
<script type="text/javascript" src="https://www.google.com/jsapi"></script>
<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script type="text/javascript">

// Load the Visualization API and the piechart package.
google.load('visualization', '1', {'packages':['table']});

// Set a callback to run when the Google Visualization API is loaded.
google.setOnLoadCallback(drawChart);

function drawChart() {
  var jsonData = $.ajax({
      url: "getData.php",
      dataType:"json",
      async: false
      }).responseText;
   var dataTable = new google.visualization.DataTable();
        dataTable.addColumn('string','category');
        dataTable.addColumn('string','context');
        dataTable.addColumn('number','id');
        dataTable.addColumn('string','location_subtype');
        dataTable.addColumn('string','location_type');
        dataTable.addColumn('string','month');
        dataTable.addColumn('string','persistent_id');
        dataTable.addColumn('string','street name');
        dataTable.addColumn('string','outcome status');

        json=JSON.parse(jsonData);
        var counter = 0;
        var countAntiSocial = 0;
        var countBurglary = 0;
        var countCriminal = 0;
        var countDrugs = 0;
        var countOtherTheft = 0;
        var countPublicDisorder = 0;
        var countRobbery = 0;
        var countShoplifting = 0;
        var countVehicleCrime = 0;
        var countViolentCrime = 0;
        var countOtherCrime = 0;
    for (var i=0; i<json.length; i++) {
        var row = [];       
        row.push(json[i].category);
        row.push(json[i].context);
        row.push(json[i].id);
        row.push(json[i].location_subtype);
        row.push(json[i].location_type);
        row.push(json[i].month);
        row.push(json[i].persistent_id);
        row.push(json[i].location.street.name);
        row.push(json[i].outcome_status ? json[i].outcome_status.category : "null");
        dataTable.addRow(row);
                    //escaping the nulls
        if(json[i].outcome_status.category != null) {
            if(json.outcome_status.category == "anti-social-behavior"){
                countAntiSocial = countAntisocial + 1;
            }

            if(json[i].outcome_status.category == "burglary"){
                countBurglary = countBurglary + 1
            }

            if(json[i].outcome_status.category == "criminal-damage-arson"){
                countCriminal = countCriminal + 1;
            }

            if(json[i].outcome_status.category == "drugs"){
                countDrugs = countDrugs + 1;
            }

            if(json[i].outcome_status.category == "other-theft"){
                countOtherTheft = countOtherTheft + 1;
            }

            if(json[i].outcome_status.category == "public-disorder-weapons"){
                countPublicDisorder = countPublicDisorder + 1;
            }

            if(json[i].outcome_status.category == "robbery"){
                countRobbery = countRobbery + 1;
            }

            if(json[i].outcome_status.category == "shoplifting"){
                countShopLifting = countShopLifting + 1;
            }

            if(json[i].outcome_status.category == "vehicle-crime"){
                countVehicleCrime = countVehicleCrime + 1;
            }

            if(json[i].outcome_status.category == "violent-crime"){
                countViolentCrime = countViolentCrime + 1;
            }

            if(json[i].outcome_status.category == "other-crime"){
                countOtherCrime = countOtherCrime + 1;
                alert(countOtherCrime);
            }
        }
    }
        var chart = new google.visualization.Table(document.getElementById('chart_div'));
        chart.draw(dataTable, {width: 1000, height: 300});

}          
</script>

和我的PHP：

<?php
$json = file_get_contents('http://data.police.uk/api/crimes-street/all-crime?lat=52.629729&lng=-1.131592&date=2013-01'); 
$json = str_replace("\xe2\x80\xa8", '\\u2028', $json);
$json = str_replace("\xe2\x80\xa9", '\\u2029', $json);
echo $json;
?>

如果有人能发现什么是错误，那将是值得赞赏的。干杯

Answer 1

问题是json[i].outcome_status未定义，然后您尝试访问该属性。没有category属性可以拥有值，因为您希望该属性存在的对象本身不存在。

你在这处理：

row.push(json[i].outcome_status ? json[i].outcome_status.category : "null");

因为该代码本质上是：如果json[i].outcome_status未定义，则返回其类别，否则返回字符串"null"。

但是，你不会在这里处理两行：

if(json[i].outcome_status.category != null) {

应该是：

if(json[i].outcome_status != null && json[i].outcome_status.category != null)

基本上，如果它具有结果状态并且具有属于真值的属性类别，请执行内部代码。

Answer 2

尝试

if(!!json[i].outcome_status.category) {

not-not子句非常方便！

编辑：

row.push((!!json[i].outcome_status && !!json[i].outcome_status.category) ? json[i].outcome_status.category : "null");

试图在json中转义null属性，但仍然得到＆＃34; TypeError：json.outcome_status未定义＆＃34;

2 个答案: