Google maps 谷歌地图绘制多边形并删除上一个多边形

当用户选择“多边形绘制”按钮绘制新多边形时，我尝试删除现有多边形。 它必须与

drawingManager.setMap（null）相关但我无法在我的代码中使用它。我试过很多东西，但都想不出来

信息：
加载页面时，默认情况下，drawingmode设置为polygon:
drawingmode:google.maps.drawing.OverlyType.polygon

用户可以绘制多边形来标记区域。多边形完成后，DrawingMode设置为null:
drawingManager.setDrawingMode（null）
和坐标被放入一个inputfield中，以便稍后通过表单将它们保存在数据库中

谁能帮帮我吗？以下是我目前的代码：

var map;
var drawingManager;    

function initialize() {
var myLatlng = new google.maps.LatLng(51.51686166794058, 3.5945892333984375);
var mapOptions = {
    zoom: 9,
    center: myLatlng,
    mapTypeId: google.maps.MapTypeId.ROADMAP
}

//Getting map DOM element
var mapElement = document.getElementById('map_canvas');

map = new google.maps.Map(map_canvas, mapOptions);

drawingManager = new google.maps.drawing.DrawingManager({
    drawingMode: google.maps.drawing.OverlayType.POLYGON,
    drawingControl: true,
    drawingControlOptions: {
        position: google.maps.ControlPosition.TOP_CENTER,
        drawingModes: [google.maps.drawing.OverlayType.POLYGON]
    },
    polygonOptions: {
        editable: true,
        draggable: true
    }
});

drawingManager.setMap(map);

// Add a listener for creating new shape event.
google.maps.event.addListener(drawingManager, "overlaycomplete", function(event) {
    var newShape = event.overlay;
    newShape.type = event.type;
    if(drawingManager.getDrawingMode()) {
        drawingManager.setDrawingMode(null);
    }

});

// Add a listener for the "drag" event.
google.maps.event.addListener(drawingManager, "overlaycomplete", function(event){
    overlayDragListener(event.overlay);
    $('#vertices').val(event.overlay.getPath().getArray());
});
}    

function overlayDragListener(overlay) {
google.maps.event.addListener(overlay.getPath(), 'set_at', function(event){
    $('#vertices').val(overlay.getPath().getArray());
});
google.maps.event.addListener(overlay.getPath(), 'insert_at', function(event){
    $('#vertices').val(overlay.getPath().getArray());
});
}

google.maps.event.addDomListener(window, 'load', initialize);

两件事：

添加全局数组（或变量）以允许访问形状
添加
drawingmode\u changed
事件处理程序，当绘图模式更改回非空时，删除所有现有多边形


var shapes = [];

google.maps.event.addListener(drawingManager, "drawingmode_changed", function() {
    if (drawingManager.getDrawingMode() != null) {
      for (var i=0; i < shapes.length; i++) {
        shapes[i].setMap(null);
      }
      shapes = [];
    }
});