根据 Bootstrap select 输入更新 ngx-leaflet 地图

Question

我有一个应用程序，当您在基于的 ngx-leaflet 中单击地图上的多边形时，它会更新 Bootstrap select 输入下拉菜单。我还希望能够 select 来自 select 输入的多边形名称并具有与单击事件相同的功能——在本例中，使用 fitBounds 平移和缩放到selected 多边形。

我将事件绑定添加到我的 HTML 模板，它从下拉菜单中检测每个新的 selection。我向该事件传递了一个新函数 onChange()。但我很难过从这里去哪里。在点击事件中，我可以使用 e.target 访问 selected 多边形的边界。但是在 onChange() 中，我只能访问 selected 多边形的名称，但我实际上并没有与该多边形关联的几何图形。那么我如何使用下拉菜单 select 输入到 select 多边形名称并让地图更新与该名称关联的多边形？（请注意，我希望得到灵活的回应，因为我想在这个示例之外的实际应用程序中做的不仅仅是 fitBounds()。）

这是我的示例代码：

polygons.geojson（在 assets 文件夹中）

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "stroke": "#555555",
        "stroke-width": 2,
        "stroke-opacity": 1,
        "fill": "#555555",
        "fill-opacity": 0.5,
        "name": "poly1"
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -121.95098876953125,
              46.82966386051541
            ],
            [
              -121.78482055664061,
              46.82966386051541
            ],
            [
              -121.78482055664061,
              46.91368905872705
            ],
            [
              -121.95098876953125,
              46.91368905872705
            ],
            [
              -121.95098876953125,
              46.82966386051541
            ]
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "stroke": "#555555",
        "stroke-width": 2,
        "stroke-opacity": 1,
        "fill": "#555555",
        "fill-opacity": 0.5,
        "name": "poly2"
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -121.77726745605469,
              46.83107318799318
            ],
            [
              -121.62963867187499,
              46.83107318799318
            ],
            [
              -121.62963867187499,
              46.913220009605624
            ],
            [
              -121.77726745605469,
              46.913220009605624
            ],
            [
              -121.77726745605469,
              46.83107318799318
            ]
          ]
        ]
      }
    }
  ]
}

app.component.html

<div class="map"
  leaflet
  [leafletLayers]="layers"
     [leafletFitBounds]="fitBounds"></div>
<div class="form-group">
  <select [(ngModel)]="selected" class="form-control" id="selectRegion" [value]="clicked" (change)="onChange()">
    <option *ngFor="let region of regions">{{ region }}</option>
  </select>
</div>

app.component.ts

import {Component, NgZone, OnInit} from '@angular/core';
import { HttpClient } from '@angular/common/http';

import * as L from 'leaflet';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {

  layers: L.Layer[];
  fitBounds = [[46.67, -122.25], [47.01, -121.302]];
  regions = [];
  clicked = '';
  selected = '';

  constructor(private http: HttpClient, private zone: NgZone) { }

  ngOnInit() {

    // read in geojson of poly
    this.http.get<any>('/assets/polygons.geojson')
      .subscribe(poly => {

        const tileLayer = L.tileLayer('https://cartodb-basemaps-{s}.global.ssl.fastly.net/light_nolabels/{z}/{x}/{y}.png', {
          subdomains: 'abcd',
          maxZoom: 19
        });

        const polyLayer = L.geoJSON(poly, {
          onEachFeature: this.onEachFeature.bind(this)
        });

        this.layers = [ tileLayer, polyLayer ];
      });
  }

  // loop through each feature of polyLayer
  onEachFeature(feature, layer) {
    this.zone.run(() => {
      // push polygon names to regions array
      this.regions.push(feature.properties.name);

      layer.on('click', <LeafletMouseEvent> (e) => {
        this.zone.run(() => {
          this.fitBounds = e.target.getBounds();
          this.clicked = e.target.feature.properties.name;
        });
      });
    });
  }

  onChange() {
    console.log(this.selected);
  }
}

Answer 1

如果要为select输入绑定对象，应该使用[ngValue]显式设置值对象：

<div class="map"
     leaflet
     [leafletLayers]="layers"
     [leafletFitBounds]="fitBounds"></div>

<div class="form-group">
  <select class="form-control" id="selectRegion"
          (change)="onChange()"
          [(ngModel)]="selected" >
    <option *ngFor="let region of regions"
            [ngValue]="region">{{ region }}</option>
  </select>
</div>

但是，您仍然遇到问题，现在您必须在单击地图时将 selected 设置为区域对象。因此，您可能需要更改地图点击代码的工作方式，以确保您在点击地图时可以获得对正确对象的引用。

Answer 2

我能够通过在 constructor() 之前首先将 polyLayer 初始化为我的应用程序组件 class 顶部的空属性来解决这个问题。因此，我在其余代码中将 polyLayer 的实例更新为 this.polyLayer。有了这个，我现在可以访问 onChange() 内的多边形，使用 eachLayer() 进行过滤，并适合地图的边界：

app.component.ts更新

import {Component, NgZone, OnInit} from '@angular/core';
import { HttpClient } from '@angular/common/http';

import * as L from 'leaflet';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {

  layers: L.Layer[];
  fitBounds = [[46.67, -122.25], [47.01, -121.302]];
  regions = [];
  clicked = '';
  selected = '';
  polyLayer = null;

  constructor(private http: HttpClient, private zone: NgZone) { }

  ngOnInit() {

    // read in geojson of poly
    this.http.get<any>('/assets/polygons.geojson')
      .subscribe(poly => {

        const tileLayer = L.tileLayer('https://cartodb-basemaps-{s}.global.ssl.fastly.net/light_nolabels/{z}/{x}/{y}.png', {
          subdomains: 'abcd',
          maxZoom: 19
        });

        this.polyLayer = L.geoJSON(poly, {
          onEachFeature: this.onEachFeature.bind(this)
        });

        this.layers = [ tileLayer, this.polyLayer ];
      });
  }

  // loop through each feature of polyLayer
  onEachFeature(feature, layer) {
    this.zone.run(() => {
      // push polygon names to regions array
      this.regions.push(feature.properties.name);

      layer.on('click', <LeafletMouseEvent> (e) => {
        this.zone.run(() => {
          this.fitBounds = e.target.getBounds();
          this.clicked = e.target.feature.properties.name;
        });
      });
    });
  }

  onChange() {

    let that = this;

    // console.log(this.polyLayer._layers);
    this.polyLayer.eachLayer(function(layer){
      if(layer.feature.properties.name === that.selected){
        that.fitBounds = layer.getBounds();
      }
    });
  }
}

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