我是一名长期潜水者，第一次发布帖子，请温柔点……
我正在构建一个地图，使用从MYSQL数据库中通过PHP解析的数据来设置由geoJson文件定义的多边形的颜色（它使用此Google开发者网站上的示例作为模板）。我的问题是，当页面加载时，数据层不会自动初始化。
下面是完整的javascript / HTML代码，但是我正在遵循的示例中用于初始化数据层的代码部分是：
google.maps.event.addListenerOnce(map.data, 'addfeature', function() {
google.maps.event.trigger(document.getElementById('price_select'),
'change');
});
这给我报错："无法读取未定义属性'setProperty'"。如果我注释掉监听器，数据层将正常加载，但只有在我手动从下拉列表（id='price_select'）中选择新输入后才会加载。
我正在加载的geoJson文件相对较大（~14mb），因此我认为发生的情况是监听器在整个文件加载之前触发（'addfeature'仅等待第一个要素添加，但我有>2000），因此由PHP解析的区划尚未具有相应的要素ID，该ID由loadGeoJson调用中的
idPropertyName：'Name'参数设置。然而，我不知道如何设置监听器仅在整个GeoJson文件加载完成后才触发。或者，我可能完全错了，这不是错误的原因。无论如何，以下是完整代码 - 我知道它有一些怪癖（例如，我向loadData函数传递了一个参数，但没有使用它），但这主要是因为我打算以后添加更多功能。感谢您与我同行！
<script src="https://maps.googleapis.com/maps/api/js?v=3.exp"></script>
<script>
var map;
var priceMin = 1000000;
var priceMax = 0;
google.maps.event.addDomListener(window, 'load', function(){
map = new google.maps.Map(document.getElementById('map-canvas'), {
center: new google.maps.LatLng(53.587425,-1.663539),
zoom: 7,
});
// add styles
map.data.setStyle(styleFeature);
map.data.addListener('mouseover', mouseInToRegion);
map.data.addListener('mouseout', mouseOutOfRegion);
// initiate drop down functionality
var selectBox = document.getElementById('price_select');
google.maps.event.addDomListener(selectBox, 'change', function() {
clearData();
loadData(selectBox.options[selectBox.selectedIndex].value);
});
// load polygons
loadMapShapes();
});
function loadMapShapes(){
map.data.loadGeoJson('http://localhost/OS_raw.json',
{ idPropertyName: 'Name' });
//This is the listener that is supposed to initiate the data layer
google.maps.event.addListenerOnce(map.data, 'addfeature', function() {
google.maps.event.trigger(document.getElementById('price_select'),
'change');
});
// End listener
}
function loadData(variable){
var phpdistricts = (<?php echo $phpdistricts; ?>);
var phpprices = (<?php echo $phpprices; ?>);
for(var i=0; i<phpdistricts.length; i++){
var district = phpdistricts[i];
var price = parseInt(phpprices[i]);
// keep track of min and max values
if (price < priceMin) {
priceMin = price;
}
if (price > priceMax) {
priceMax = price;
}
console.log(map.data.getFeatureById(district));
//This is where the error triggers - feature is undefined according to console log above
map.data
.getFeatureById(district)
.setProperty('price', price);}
//end of problematic section
// update and display the legend
document.getElementById('census-min').textContent =
priceMin.toLocaleString();
document.getElementById('census-max').textContent =
priceMax.toLocaleString();
}
function clearData() {
priceMin = 1000000;
priceMax = 0;
map.data.forEach(function(row) {
row.setProperty('price', undefined);
});
document.getElementById('data-box').style.display = 'none';
document.getElementById('data-caret').style.display = 'none';
}
function styleFeature(feature) {
var low = [151, 83, 34]; // color of smallest datum
var high = [5, 69, 54]; // color of largest datum
// delta represents where the value sits between the min and max
var delta = (feature.getProperty('price') - priceMin) /
(priceMax - priceMin);
var color = [];
for (var i = 0; i < 3; i++) {
// calculate an integer color based on the delta
color[i] = (high[i] - low[i]) * delta + low[i];
}
// filters out areas without data
var showRow = true;
if (feature.getProperty('price') == null ||
isNaN(feature.getProperty('price'))) {
showRow = false;
}
var outlineWeight = 0.5, zIndex = 1;
if (feature.getProperty('state') === 'hover') {
outlineWeight = zIndex = 2;
}
return {
strokeWeight: outlineWeight,
strokeColor: '#fff',
zIndex: zIndex,
fillColor: 'hsl(' + color[0] + ',' + color[1] + '%,' + color[2] + '%)',
fillOpacity: 0.75,
visible: showRow
};
}
function mouseInToRegion(e) {
// set the hover state so the setStyle function can change the border
e.feature.setProperty('state', 'hover');
var percent = (e.feature.getProperty('price') - priceMin) /
(priceMax - priceMin) * 100;
// update the label
document.getElementById('data-label').textContent =
e.feature.getProperty('Name');
document.getElementById('data-value').textContent =
e.feature.getProperty('price');
document.getElementById('data-box').style.display = 'block';
document.getElementById('data-caret').style.display = 'block';
document.getElementById('data-caret').style.paddingLeft = percent + '%';
}
function mouseOutOfRegion(e) {
// reset the hover state, returning the border to normal
e.feature.setProperty('state', 'normal');
}
</script>
</head>
<body>
<div id="controls" class="nicebox">
<div>
<select id="price_select">
<option value="price">Jun '14</option>
<option value="price">Jun '14</option>
</select>
</div>
<div id="legend">
<div id="census-min">min</div>
<div class="color-key">
<span id="data-caret">◆</span>
</div>
<div id="census-max">max</div>
</div>
</div>
<div id="data-box" class="nicebox">
<label id="data-label" for="data-value">Area: </label>
<span id="data-value"></span>
</div>
<div id="map-canvas"></div>
</body>
</html>