在 Blazor SPA 上嵌入 Leaflet 地图

Question

如何使用 JSInterop 在 Blazor SPA 上嵌入 Leaflet 地图，应定义哪些对象，以及如何传递表示在地图上单击的位置的数据，从 JavaScript 到 Blazor

Answer 1

注意：下面的示例代码是在独立的 WebAssembly Blazor 应用程序中创建和测试的...

An object reference is required for the nonstatic field, method, or property 'member'

让我们创建对象 class，其对象引用将在初始化时传递给您 JavaScript 的对象。当用户点击地图上的某个位置时，会触发JS地图对象的点击事件，从中调用C#对象的JSInvokable方法并传递经纬度...

GCSService.cs

public class GCSService
{
    public GCSService() {}
    public event Func<Task> Notify;
    public string LatLng { get; set; }

    [JSInvokableAttribute("GetLatLng")]
    public async Task GetLatLng(string latLng)
    {
       LatLng = latLng;

       if (Notify != null)
       {
           await Notify?.Invoke();
       }
    }
}

注意名为 Notify 的事件委托的定义。此事件被触发每当 LatLng 属性的值从 JavaScript 更改时。这允许您订阅事件，并调用 StateHasChanged 方法以刷新 UI.

Index.razor

@page "/"
@implements IDisposable
@inject IJSRuntime JSRuntime

@if (GCS != null)
{
    <div>Latitude and Longitude: @GCS.LatLng</div>
}
<div id="mapid"></div>

@code{
    private DotNetObjectReference<GCSService> objRef;
    private GCSService GCS;

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            await JSRuntime.InvokeAsync<object>(
            "leafletJsFunctions.initialize", objRef);
        }
        base.OnAfterRender(firstRender);
    }

    protected override void OnInitialized()
    {
        GCS = new GCSService();

        objRef = DotNetObjectReference.Create(GCS);

        GCS.Notify += OnNotify;
    }

    public void Dispose()
    {
        GCS.Notify -= OnNotify;

        objRef?.Dispose();
    }

    public async Task OnNotify()
    {
        await InvokeAsync(() =>
        {
            StateHasChanged();
        });
   }
 }

将此 CSS 规则添加到 app.css:

#mapid {
    height: 400px;
}

请注意，您的 JavaScript 对象仅从 OnAfterRenderAsync 生命周期方法初始化一次...

这里是相关的 JavaScript 代码，应该放在 index.html 文件的底部，在 blazor.webassembly.js

的脚本元素下面

<link rel="stylesheet" href="https://unpkg.com/leaflet@1.7.1/dist/leaflet.css"
          integrity="sha512-xodZBNTC5n17Xt2atTPuE1HxjVMSvLVW9ocqUKLsCC5CXdbqCmblAshOMAS6/keqq/sMZMZ19scR4PsZChSR7A=="
          crossorigin="" />

<!-- Make sure you put this AFTER Leaflet's CSS -->
<script src="https://unpkg.com/leaflet@1.7.1/dist/leaflet.js"
        integrity="sha512-XQoYMqMTK8LvdxXYG3nZ448hOEQiglfqkJs1NOQV44cWnUrBc8PkAOcXy20w0vlaXaVUearIOBhiXZ5V3ynxwA=="
        crossorigin="">

</script>

<script type="text/javascript">
    window.leafletJsFunctions = {
        initialize: function (dotnetHelper) {
            var mymap = L.map('mapid').setView([51.505, -0.09], 13);
            L.tileLayer('https://api.mapbox.com/styles/v1/{id}/tiles/{z}/{x}/{y}?access_token=pk.eyJ1IjoibWFwYm94IiwiYSI6ImNpejY4NXVycTA2emYycXBndHRqcmZ3N3gifQ.rJcFIG214AriISLbB6B5aw', {
                maxZoom: 18,
                attribution: 'Map data &copy; <a href="https://www.openstreetmap.org/">OpenStreetMap</a> contributors, ' +
                    '<a href="https://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, ' +
                    'Imagery © <a href="https://www.mapbox.com/">Mapbox</a>',
                id: 'mapbox/streets-v11',
                tileSize: 512,
                zoomOffset: -1
            }).addTo(mymap);

            L.marker([51.5, -0.09]).addTo(mymap)
                .bindPopup("<b>Hello world!</b><br />I am a popup.").openPopup();

            L.circle([51.508, -0.11], 500, {
                color: 'red',
                fillColor: '#f03',
                fillOpacity: 0.5
            }).addTo(mymap).bindPopup("I am a circle.");

            L.polygon([
                [51.509, -0.08],
                [51.503, -0.06],
                [51.51, -0.047]
            ]).addTo(mymap).bindPopup("I am a polygon.");

            var popup = L.popup();

            function onMapClick(e) {
                // Invoke the instance method GetLatLng, passing it the
                // Latitude and Logitude value
                return dotnetHelper.invokeMethodAsync('GetLatLng',
                                            e.latlng.toString());
             }

            mymap.on('click', onMapClick);
       }
     };
</script>

在 Blazor SPA 上嵌入 Leaflet 地图

Embedding a Leaflet map on a Blazor SPA

leaflet

blazor

blazor-server-side

blazor-client-side

blazor-webassembly

GCSService.cs

Index.razor