cesium鼠标滚轮实现geojson的动态加载

有这样一个需求：

当鼠标滚轮向下滚动时，动态加载geojson数据，而向上滚动时，数据自动恢复原样。 1.gif
首先需要加载出全国的geojson数据，当选择某个省的时候，拾取到这个省的行政码信息，然后请求加载这个省的geojson数据。

我们可以用MOUSE_MOVE事件，获取鼠标移动时的坐标，从而拾取到这个物体，然后在鼠标滚轮WHEEL事件中，通过上下方向以及层级的判断来触发加载数据。

async addGeoJsonData(code) {//获取接口数据
      let data = await getGeojsonApi({ admincode: code })
      ...
},
setAction() {
            const Cesium = this.Cesium
            //球交互事件
            this.handler = new Cesium.ScreenSpaceEventHandler(this.viewer.scene.canvas)

            let leftclick = Cesium.ScreenSpaceEventType.MOUSE_MOVE
            this.viewer.screenSpaceEventHandler.removeInputAction(leftclick)
            this.handler.setInputAction((e) => {
                // let pickObj = this.viewer.scene.pick(e.position)
                // console.log(pickObj, e.position)
                let pickObj = this.viewer.scene.pick(e.endPosition)
                // 视角飞入
                if (pickObj && pickObj.id) {

                    this.pickObj = pickObj;
                }
            }, leftclick);
            let wheel = Cesium.ScreenSpaceEventType.WHEEL;
            this.handler.setInputAction((wheel) => {
                // let pickObj = this.viewer.scene.pick(e.position)
                console.log('wheeel>>>',wheel);
                let tiles = new Set();
                let tilesToRender = this.viewer.scene.globe._surface._tilesToRender;
                if(Cesium.defined(tilesToRender)){
                    for(let i=0;i<tilesToRender.length;i++){
                        
                        tiles.add(tilesToRender[i].level);
                    }
                    // console.log('当前地图瓦片级别为',tiles);
                    // console.log(Math.max(...tiles));
                    let level = Math.max(...tiles);
                    console.log('level',level);
                    if(wheel > 0) {//当放低镜头时
                    console.log('放低镜头');
                        if(this.pickObj) {
                            let pickObj = this.pickObj;
                            if(level > 3) {
                                //查询geojson
                                this.addGeoJsonData(`${pickObj.id.admincode}`)
                                
                            } 
                        }



                    } else {
                        console.log('拉高镜头');
                        if(level < 5) { //只有当拉高镜头时，清除数据

                            this.code = '';
                            this.hideGeoJsonData();
                            this.showGeoJsonData('100000_full');
                            Object.keys(this.labelCont).map(item=>this.labelCont[item].show = true);

                        }
                    }
                    

                }
            },wheel);

        },

但这样做有个问题，就是会频繁触发addGeoJsonData函数，从而导致数据重复叠加。我希望一个admincode行政区的数据仅加载一次。
我们可以利用watch来解决这个问题。

data() {
  return {
    code: ''
  }
},
watch: {
        code: {
            handler(val, oldVal) {
                
                if(val !== oldVal) {
                    
                    this.addGeoJsonData(val);
                    
                }
            },
            deep: true,
            immediate: true
        },
},
methods: {
    async addGeoJsonData(code) {//获取接口数据
          let data = await getGeojsonApi({ admincode: code })
          ...
    },
    setAction() {
            const Cesium = this.Cesium
            //球交互事件
            this.handler = new Cesium.ScreenSpaceEventHandler(this.viewer.scene.canvas)

            let leftclick = Cesium.ScreenSpaceEventType.MOUSE_MOVE
            this.viewer.screenSpaceEventHandler.removeInputAction(leftclick)
            this.handler.setInputAction((e) => {
                // let pickObj = this.viewer.scene.pick(e.position)
                // console.log(pickObj, e.position)
                let pickObj = this.viewer.scene.pick(e.endPosition)
                // 视角飞入
                if (pickObj && pickObj.id) {

                    this.pickObj = pickObj;
                }
            }, leftclick);
            let wheel = Cesium.ScreenSpaceEventType.WHEEL;
            this.handler.setInputAction((wheel) => {
                // let pickObj = this.viewer.scene.pick(e.position)
                console.log('wheeel>>>',wheel);
                let tiles = new Set();
                let tilesToRender = this.viewer.scene.globe._surface._tilesToRender;
                if(Cesium.defined(tilesToRender)){
                    for(let i=0;i<tilesToRender.length;i++){
                        
                        tiles.add(tilesToRender[i].level);
                    }
                    // console.log('当前地图瓦片级别为',tiles);
                    // console.log(Math.max(...tiles));
                    let level = Math.max(...tiles);
                    console.log('level',level);
                    if(wheel > 0) {//当放低镜头时
                    console.log('放低镜头');
                        if(this.pickObj) {
                            let pickObj = this.pickObj;
                            if(level > 3) {
                                //查询geojson
                                this.code = pickObj.id.admincode;
                                
                            } 
                        }



                    } else {
                        console.log('拉高镜头');
                        if(level < 5) { //只有当拉高镜头时，清除数据

                            this.code = '';
                            this.hideGeoJsonData();
                            this.showGeoJsonData('100000_full');
                            Object.keys(this.labelCont).map(item=>this.labelCont[item].show = true);

                        }
                    }
                    

                }
            },wheel);

        },
}