我正在为 Google 地图编写自定义叠加层。我有很多经纬度点，我想用箭头指向和指向它们的图像。我正在关注 Google 的自定义叠加教程（https://developers.google.com/maps/documentation/javascript/overlays#CustomOverlays）。
在我的叠加层的“构造函数”中，这一行失败：'this.setMap(this.map_);'
我需要做什么才能使其工作？
这是我的叠加层的“构造函数”。虚线位于底部。我正在测试时，所有对“警报”的调用都在那里。没有打到最后一个电话，这就是为什么我认为 'this.setMap()' 不起作用。
//This serves as a constructor for a link overlay
function LinkOverlay(startNodeCoordinates, endNodeCoordinates, map)
{
alert("constructor start");
this.map_ = map;
//These are the lat-long coordinates of where the link starts and ends
this.startNodeCoordinates_ = startNodeCoordinates;
this.endNodeCoordinates_ = endNodeCoordinates;
alert("constructor coordinates stored");
// We define a property to hold the image's
// div. We'll actually create this div
// upon receipt of the add() method so we'll
// leave it null for now.
this.div_ = null;
alert("constructor div saved");
//We need to know if we draw the arrow up or down and left or right.
//We calculate this by finding the bearing between the two nodes. If
//the bearing is N to NE, then the arrow goes up and to the right,
//for example. If the bearing is E to SE, then the arrow goes down
//and to the right, and so on.
//Calculate bearing
/*
* This algorithm determines the bearing (or angle) between two coordinate points.
* It was adapted from http://www.movable-type.co.uk/scripts/latlong.html
*/
alert("constructor calculating bearing")
this.bearing_ = null;
var lat1 = this.startNodeCoordinates_.lat();
var lat2 = this.endNodeCoordinates_.lat();
var dLon = this.startNodeCoordinates_.lng() - this.endNodeCoordinates_.lng();
var y = Math.sin(dLon) * Math.cos(lat2);
var x = Math.cos(lat1)*Math.sin(lat2) -
Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);
this.bearing_ = Math.atan2(y, x);
alert("constructor bearing found (bearing = " + this.bearing_ + ")");
this.arrowUp_ = null;
this.arrowRight_ = null;
this.image_ = null;
alert("constructor picking image");
if((this.bearing_ >= 0 && this.bearing_ < (Math.PI * 0.5)) || this.bearing_ == (Math.PI * 2))
{
alert("constructor NE");
//If bearing is N to NE, the arrow goes up and to the right
this.arrowUp_ = new Boolean(true);
this.arrowRight_ = new Boolean(true);
this.image_ = "../../Content/map_images/link_overlay/up_right_black.png";
}
else if(this.bearing_ >= (Math.PI * 0.5) && this.bearing_ < Math.PI)
{
alert("constructor SE");
//If bearing is E to SE, the arrow goes down and to the right
this.arrowUp_ = new Boolean(false);
this.arrowRight_ = new Boolean(true);
this.image_ = "../../Content/map_images/link_overlay/down_right_black.png";
}
else if(this.bearing_ >= Math.PI && this.bearing_ < (Math.PI * 1.5))
{
alert("constructor SW");
//If bearing is S to SW, the arrow goes down and to the left
this.arrowUp_ = new Boolean(false);
this.arrowRight_ = new Boolean(false);
this.image_ = "../../Content/map_images/link_overlay/down_left_black.png";
}
else
{
alert("constructor NW");
//If bearing is W to NW, the arrow goes up and to the left
this.arrowUp_ = new Boolean(true);
this.arrowRight_ = new Boolean(false);
this.image_ = "../../Content/map_images/link_overlay/up_left_black.png";
}
alert("constructor adding to map");
// Explicitly call setMap() on this overlay
this.setMap(this.map_);
alert("constructor end");
}
//This "subclasses" a link overlay from Google Map's OverlayView class
LinkOverlay.prototype = new google.maps.OverlayView();
这是创建新 LinkOverlays 的代码（在 Razor 语法中）：
@:var startNodeCoordinates = new google.maps.LatLng('@startNode.Latitude', '@startNode.Longitude');
@:var endNodeCoordinates = new google.maps.LatLng('@endNode.Latitude', '@endNode.Longitude');
@:var routeLine = new LinkOverlay(startNodeCoordinates, endNodeCoordinates, networkMap);