问题：如题，百度地图API 在使用点聚合时，如果放大、缩小或移动地图时，添加的文字标签（label）会消失。
原因：API代码中的map.removeOverlay(marker)，在这句话执行的时候，会自动将marker.label =null；
解决：在每次removeOverlay之前先获取到label，方法为getLabel，removeOverlay之后再设置label，方法为setLabel。
完整的代码为将http://api.map.baidu.com/library/MarkerClusterer/1.2/src/MarkerClusterer_min.js的代码完全替换为下列代码：
var BMapLib = window.BMapLib = BMapLib || {};
(function() {
var getExtendedBounds = function(map, bounds, gridSize) {
bounds = cutBoundsInRange(bounds);
var pixelNE = map.pointToPixel(bounds.getNorthEast());
var pixelSW = map.pointToPixel(bounds.getSouthWest());
pixelNE.x += gridSize;
pixelNE.y -= gridSize;
pixelSW.x -= gridSize;
pixelSW.y += gridSize;
var newNE = map.pixelToPoint(pixelNE);
var newSW = map.pixelToPoint(pixelSW);
return new BMap.Bounds(newSW, newNE)
};
var cutBoundsInRange = function(bounds) {
var maxX = getRange(bounds.getNorthEast().lng, -180, 180);
var minX = getRange(bounds.getSouthWest().lng, -180, 180);
var maxY = getRange(bounds.getNorthEast().lat, -74, 74);
var minY = getRange(bounds.getSouthWest().lat, -74, 74);
return new BMap.Bounds(new BMap.Point(minX, minY), new BMap.Point(maxX, maxY))
};
var getRange = function(i, mix, max) {
mix && (i = Math.max(i, mix));
max && (i = Math.min(i, max));
return i
};
var isArray = function(source) {
return '[object Array]' === Object.prototype.toString.call(source)
};
var indexOf = function(item, source) {
var index = -1;
if (isArray(source)) {
if (source.indexOf) {
index = source.indexOf(item)
} else {
for (var i = 0,
m; m = source[i]; i++) {
if (m === item) {
index = i;
break
}
}
}
}
return index
};
var MarkerClusterer = BMapLib.MarkerClusterer = function(map, options) {
if (!map) {
return
}
this._map = map;
this._markers = [];
this._clusters = [];
var opts = options || {};
this._gridSize = opts["gridSize"] || 60;
this._maxZoom = opts["maxZoom"] || 18;
this._minClusterSize = opts["minClusterSize"] || 2;
this._isAverageCenter = false;
if (opts['isAverageCenter'] != undefined) {
this._isAverageCenter = opts['isAverageCenter']
}
this._styles = opts["styles"] || [];
var that = this;
this._map.addEventListener("zoomend",
function() {
that._redraw()
});
this._map.addEventListener("moveend",
function() {
that._redraw()
});
var mkrs = opts["markers"];
isArray(mkrs) && this.addMarkers(mkrs)
};
MarkerClusterer.prototype.addMarkers = function(markers) {
for (var i = 0,
len = markers.length; i < len; i++) {
this._pushMarkerTo(markers[i])
}
this._createClusters()
};
MarkerClusterer.prototype._pushMarkerTo = function(marker) {
var index = indexOf(marker, this._markers);
if (index === -1) {
marker.isInCluster = false;
this._markers.push(marker)
}
};
MarkerClusterer.prototype.addMarker = function(marker) {
this._pushMarkerTo(marker);
this._createClusters()
};
MarkerClusterer.prototype._createClusters = function() {
var mapBounds = this._map.getBounds();
var extendedBounds = getExtendedBounds(this._map, mapBounds, this._gridSize);
for (var i = 0,
marker; marker = this._markers[i]; i++) {
if (!marker.isInCluster && extendedBounds.containsPoint(marker.getPosition())) {
this._addToClosestCluster(marker)
}
}
};
MarkerClusterer.prototype._addToClosestCluster = function(marker) {
var distance = 4000000;
var clusterToAddTo = null;
var position = marker.getPosition();
for (var i = 0,
cluster; cluster = this._clusters[i]; i++) {
var center = cluster.getCenter();
if (center) {
var d = this._map.getDistance(center, marker.getPosition());
if (d < distance) {
distance = d;
clusterToAddTo = cluster
}
}
}
if (clusterToAddTo && clusterToAddTo.isMarkerInClusterBounds(marker)) {
clusterToAddTo.addMarker(marker)
} else {
var cluster = new Cluster(this);
cluster.addMarker(marker);
this._clusters.push(cluster)
}
};
MarkerClusterer.prototype._clearLastClusters = function() {
for (var i = 0,
cluster; cluster = this._clusters[i]; i++) {
cluster.remove()
}
this._clusters = [];
this._removeMarkersFromCluster()
};
MarkerClusterer.prototype._removeMarkersFromCluster = function() {
for (var i = 0,
marker; marker = this._markers[i]; i++) {
marker.isInCluster = false
}
};
MarkerClusterer.prototype._removeMarkersFromMap = function() {
for (var i = 0,
marker; marker = this._markers[i]; i++) {
marker.isInCluster = false;
tmplabel = marker.getLabel();
this._map.removeOverlay(marker);
marker.setLabel(tmplabel)
}
};
MarkerClusterer.prototype._removeMarker = function(marker) {
var index = indexOf(marker, this._markers);
if (index === -1) {
return false
}
tmplabel = marker.getLabel();
this._map.removeOverlay(marker);
marker.setLabel(tmplabel);
this._markers.splice(index, 1);
return true
};
MarkerClusterer.prototype.removeMarker = function(marker) {
var success = this._removeMarker(marker);
if (success) {
this._clearLastClusters();
this._createClusters()
}
return success
};
MarkerClusterer.prototype.removeMarkers = function(markers) {
var success = false;
for (var i = 0; i < markers.length; i++) {
var r = this._removeMarker(markers[i]);
success = success || r
}
if (success) {
this._clearLastClusters();
this._createClusters()
}
return success
};
MarkerClusterer.prototype.clearMarkers = function() {
this._clearLastClusters();
this._removeMarkersFromMap();
this._markers = []
};
MarkerClusterer.prototype._redraw = function() {
this._clearLastClusters();
this._createClusters()
};
MarkerClusterer.prototype.getGridSize = function() {
return this._gridSize
};
MarkerClusterer.prototype.setGridSize = function(size) {
this._gridSize = size;
this._redraw()
};
MarkerClusterer.prototype.getMaxZoom = function() {
return this._maxZoom
};
MarkerClusterer.prototype.setMaxZoom = function(maxZoom) {
this._maxZoom = maxZoom;
this._redraw()
};
MarkerClusterer.prototype.getStyles = function() {
return this._styles
};
MarkerClusterer.prototype.setStyles = function(styles) {
this._styles = styles;
this._redraw()
};
MarkerClusterer.prototype.getMinClusterSize = function() {
return this._minClusterSize
};
MarkerClusterer.prototype.setMinClusterSize = function(size) {
this._minClusterSize = size;
this._redraw()
};
MarkerClusterer.prototype.isAverageCenter = function() {
return this._isAverageCenter
};
MarkerClusterer.prototype.getMap = function() {
return this._map
};
MarkerClusterer.prototype.getMarkers = function() {
return this._markers
};
MarkerClusterer.prototype.getClustersCount = function() {
var count = 0;
for (var i = 0,
cluster; cluster = this._clusters[i]; i++) {
cluster.isReal() && count++
}
return count
};
function Cluster(markerClusterer) {
this._markerClusterer = markerClusterer;
this._map = markerClusterer.getMap();
this._minClusterSize = markerClusterer.getMinClusterSize();
this._isAverageCenter = markerClusterer.isAverageCenter();
this._center = null;
this._markers = [];
this._gridBounds = null;
this._isReal = false;
this._clusterMarker = new BMapLib.TextIconOverlay(this._center, this._markers.length, {
"styles": this._markerClusterer.getStyles()
})
}
Cluster.prototype.addMarker = function(marker) {
if (this.isMarkerInCluster(marker)) {
return false
}
if (!this._center) {
this._center = marker.getPosition();
this.updateGridBounds()
} else {
if (this._isAverageCenter) {
var l = this._markers.length + 1;
var lat = (this._center.lat * (l - 1) + marker.getPosition().lat) / l;
var lng = (this._center.lng * (l - 1) + marker.getPosition().lng) / l;
this._center = new BMap.Point(lng, lat);
this.updateGridBounds()
}
}
marker.isInCluster = true;
this._markers.push(marker);
var len = this._markers.length;
if (len < this._minClusterSize) {
this._map.addOverlay(marker);
return true
} else if (len === this._minClusterSize) {
for (var i = 0; i < len; i++) {
tmplabel = this._markers[i].getLabel();
this._markers[i].getMap() && this._map.removeOverlay(this._markers[i]);
this._markers[i].setLabel(tmplabel)
}
}
this._map.addOverlay(this._clusterMarker);
this._isReal = true;
this.updateClusterMarker();
return true
};
Cluster.prototype.isMarkerInCluster = function(marker) {
if (this._markers.indexOf) {
return this._markers.indexOf(marker) != -1
} else {
for (var i = 0,
m; m = this._markers[i]; i++) {
if (m === marker) {
return true
}
}
}
return false
};
Cluster.prototype.isMarkerInClusterBounds = function(marker) {
return this._gridBounds.containsPoint(marker.getPosition())
};
Cluster.prototype.isReal = function(marker) {
return this._isReal
};
Cluster.prototype.updateGridBounds = function() {
var bounds = new BMap.Bounds(this._center, this._center);
this._gridBounds = getExtendedBounds(this._map, bounds, this._markerClusterer.getGridSize())
};
Cluster.prototype.updateClusterMarker = function() {
if (this._map.getZoom() > this._markerClusterer.getMaxZoom()) {
this._clusterMarker && this._map.removeOverlay(this._clusterMarker);
for (var i = 0,
marker; marker = this._markers[i]; i++) {
this._map.addOverlay(marker)
}
return
}
if (this._markers.length < this._minClusterSize) {
this._clusterMarker.hide();
return
}
this._clusterMarker.setPosition(this._center);
this._clusterMarker.setText(this._markers.length);
var thatMap = this._map;
var thatBounds = this.getBounds();
this._clusterMarker.addEventListener("click",
function(event) {
thatMap.setViewport(thatBounds)
})
};
Cluster.prototype.remove = function() {
for (var i = 0,
m; m = this._markers[i]; i++) {
var tmplabel = this._markers[i].getLabel();
this._markers[i].getMap() && this._map.removeOverlay(this._markers[i]);
this._markers[i].setLabel(tmplabel)
}
this._map.removeOverlay(this._clusterMarker);
this._markers.length = 0;
delete this._markers
}
Cluster.prototype.getBounds = function() {
var bounds = new BMap.Bounds(this._center, this._center);
for (var i = 0,
marker; marker = this._markers[i]; i++) {
bounds.extend(marker.getPosition())
}
return bounds
};
Cluster.prototype.getCenter = function() {
return this._center
}
})();
