Google maps 谷歌地图apiv3标记替换旧的

我有一个小功能，可以在单击时添加一个标记和信息窗口。但是，当我单击一个新位置时，旧位置仍然存在。我想换一个新的。这是我的密码：

function MapInitialize() {

            var mapOptions = {
            zoom: 4,
            center: new google.maps.LatLng(43,-77),
            mapTypeId: google.maps.MapTypeId.ROADMAP
            }

            var map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions);
        google.maps.event.addListener(map, 'click', function(event) {
            var marker = new google.maps.Marker({
                position: event.latLng,
                map: map
        })
        var infowindow = new google.maps.InfoWindow({
                content: 'Content Here'
            });
            infowindow.open(map,marker);
});
}

---

谢谢

在创建新标记之前删除旧标记：

var marker = null;
function MapInitialize() {

            var mapOptions = {
            zoom: 4,
            center: new google.maps.LatLng(43,-77),
            mapTypeId: google.maps.MapTypeId.ROADMAP
            }

            var map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions);
        google.maps.event.addListener(map, 'click', function(event) {
            if (marker && marker.setMap) marker.setMap(null);
            marker = new google.maps.Marker({
                position: event.latLng,
                map: map
        })
        var infowindow = new google.maps.InfoWindow({
                content: 'Content Here'
            });
            infowindow.open(map,marker);
});
}