我正在制作一个应用程序，其中我拥有资产数据库，我需要查看具有特定参数的地图中的资产。我编写了代码，但是当我选择任何一个下拉框时，它会显示错误无法读取未定义的属性'lat'。地图首先出现，但在我在下拉列表中选择某个值后，它会消失。任何帮助将不胜感激。提前致谢。我也添加了cs文件和aspx文件。
<script async
src="https://maps.googleapis.com/maps/api/js?key=KEY&callback=initMap">
</script>
<script type="text/javascript">
var markers = [
<asp:Repeater ID="rptMarkers" runat="server">
<ItemTemplate>
{
"Name": '<%# Eval("AID") %>',
"lat": '<%# Eval("Current_Location_Y") %>',
"lng": '<%# Eval("Current_Location_X") %>',
"description": '<%# Eval("Description") %>'
}
</ItemTemplate>
<SeparatorTemplate>
,
</SeparatorTemplate>
</asp:Repeater >
];
</script>
<script type="text/javascript">
window.onload = function initMap() {
var mapOptions = {
center: new google.maps.LatLng(markers[0].lat, markers[0].lng),
zoom: 8,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var infoWindow = new google.maps.InfoWindow/*()*/;
var map = new google.maps.Map(document.getElementById("map"), mapOptions);
for (i = 0; i < markers.length; i++) {
var data = markers[i]
var myLatlng = new google.maps.LatLng(data.lat, data.lng);
var marker = new google.maps.Marker({
position: myLatlng,
map: map,
title: data.title
});
(function (marker, data) {
google.maps.event.addListener(marker, "click", function (e) {
infoWindow.setContent(data.Name);
infoWindow.open(map, marker);
});
})(marker, data);
}
}
</script>
<div id="DDmap" style="float:left; height: 200px">
<div id="side" style=" background-color: white;
font-size: 18px;
text-align: center; padding: 50px 20px 50px 20px;" class="auto-style3">
<asp:DropDownList ID="DDSearch" runat="server" placeholder="Select By" text-align="center" class="form-control" Height="30px" style="float:right;" Width="50%" margin="2px" AutoPostBack="True" OnSelectedIndexChanged="DDSearch_SelectedIndexChanged">
<asp:ListItem Selected="True" Value="0" Text="Select By"></asp:ListItem>
<asp:ListItem Text="Locate" Value="1"></asp:ListItem>
<asp:ListItem Text="Buffer" Value="2"></asp:ListItem>
</asp:DropDownList>
<br /> <br />
<br /> <br />
<asp:Panel ID="Search" runat="server" Visible="False">
<label for ="Search" style="float:right">
<asp:DropDownList ID="DDCondition" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDCondition_SelectedIndexChanged">
</asp:DropDownList>
<br /><br />
<asp:DropDownList ID="DDStatus" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDStatus_SelectedIndexChanged">
</asp:DropDownList>
<br /><br />
<asp:DropDownList ID="DDGroup" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDGroup_SelectedIndexChanged">
</asp:DropDownList>
</label>
<br /><br />
</asp:Panel>
</div>
aspx文件
<div class="CustomList-customListContainer"><!-- react-empty: 292 --><section class="CustomList-header"><div class="CustomList-headerCont"><div class="CustomList-heartIcon"><img class="CustomList-imageTag" src="/static-listing/images/heart.svg" alt=""></div><div class="CustomList-Settings"></div><div class="CustomList-ListHeading"><button class="CustomList-ListHeading">My Favorites</button></div></div><div class="CustomList-itemsCount"><button class="CustomList-totalItems">7 items</button></div></section><div class="CustomList-imageContainer" style="width: 50%; height: 100%;"><a href="/savedlist?id=myFavorites"><img class="CustomList-imageTag" src="https://www.concordia.ca/students/health/_jcr_content/content-main/textimage/image.img.png/1462990904049.png" alt=""></a></div><div class="CustomList-imageContainer" style="width: 25%; height: 50%;"><a href="/savedlist?id=myFavorites"><img class="CustomList-imageTag" src="https://www.concordia.ca/students/health/_jcr_content/content-main/textimage/image.img.png/1462990904049.png" alt=""></a></div><div class="CustomList-imageContainer" style="width: 25%; height: 50%;"><a href="/savedlist?id=myFavorites"><img class="CustomList-imageTag" src="https://www.concordia.ca/students/health/_jcr_content/content-main/textimage/image.img.png/1462990904049.png" alt=""></a></div><div class="CustomList-imageContainer" style="width: 25%; height: 50%;"><a href="/savedlist?id=myFavorites"><img class="CustomList-imageTag" src="https://www.concordia.ca/students/health/_jcr_content/content-main/textimage/image.img.png/1462990904049.png" alt=""></a></div><div class="CustomList-imageContainer" style="width: 25%; height: 50%; background: rgb(241, 243, 244);"><a href="/savedlist?id=myFavorites" style="
width: 100%;
height: 100%;
display: block;
"><div class="CustomList-productsCount"><!-- react-text: 327 -->+ <!-- /react-text --><!-- react-text: 328 -->3<!-- /react-text --></div></a></div></div>
答案 0 :(得分：0)
在某些时候，您正在尝试读取对象的纬度，但对象本身是未定义的。 JavaScript中的一行代码访问标记数组的第一个元素，而不检查数组是否为空：
var mapOptions = {
center: new google.maps.LatLng(markers[0].lat, markers[0].lng),
zoom: 8,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
如果没有标记，则markers[0]将评估为未定义，您将收到错误Cannot read property 'lat' of undefined。我建议先进行检查，如果列表为空，请提供默认的纬度和经度：
var center = new google.maps.LatLng(0, 0);
if (markers.length > 0)
center = new google.maps.LatLng(markers[0].lat, markers[0].lng);
var mapOptions = {
center: center,
zoom: 8,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
看起来，只要您在下拉列表中选择一个项目，就会出现以下情况：
DDSearch.SelectedValue == "1" && DDStatus.SelectedIndex >= 0 && DDCondition.SelectedIndex >= 0 && DDGroup.SelectedIndex >= 0
因此，GetData（）不会返回所有LUT_Asset_Masters，而只会返回与您的过滤器匹配的LUT_Asset_Masters，而这只是一个空列表。您需要仔细检查该查询 - 确保您查询的数据存在，并且查询返回您希望返回的内容。