WebView2 系列之-前端向后端传递文件对象

背景

WebView2 中，前端到后端的消息传递，通常是不支持传递对象的。但是我在查阅官方文档时发现了一个例外，那就是方法postMessageWithAdditionalObjects

如何传递附加对象

webview2中，前端 js 向后端传递消息通常使用 window.chrome.webview.postMessage 方法，postMessage的定义如下：

     /**
     * When the page calls postMessage, the message parameter is converted to JSON and is posted
     * asynchronously to the WebView2 host process. This will result in either the
     * CoreWebView2.WebMessageReceived event or the CoreWebView2Frame.WebMessageReceived event being
     * raised, depending on if postMessage is called from the top-level document in the WebView2
     * or from a child frame. See CoreWebView2.WebMessageReceived( Win32/C++, .NET, WinRT).
     * See CoreWebView2Frame.WebMessageReceived( Win32/C++, .NET, WinRT).
     * @param message The message to send to the WebView2 host. This can be any object that can be
     *                serialized to JSON.
     */
    postMessage(message: any) : void;

当我们使用postMessage传递任何数据类型时，都将被转为 json 字符串进行传递。

postMessageWithAdditionalObjects 接受两个参数，第一个参数和postMessage的参数一样，第二个参数允许传递一个 js 对象列表，它会被转换为原生代码中对应的类。

/**
     * When the page calls `postMessageWithAdditionalObjects`, the `message` parameter is sent to WebView2 in the same
     * fashion as {@link WebView.postMessage}.
     * Objects passed as 'additionalObjects' are converted to their native types and will be available in the
     * `CoreWebView2WebMessageReceivedEventArgs.AdditionalObjects` property.
     * @param message The message to send to the WebView2 host. This can be any object that can be serialized to JSON.
     * @param additionalObjects A sequence of DOM objects that have native representations in WebView2.
     * This parameter needs to be ArrayLike.
     *
     * The following DOM types are mapped to native:
     * DOM    | Win32              | .NET                | WinRT
     * ------ | ------------------ | ------------------- | ---------------------------
     * File   | ICoreWebView2File  | System.IO.FileInfo  | Windows.Storage.StorageFile
     *
     * `null` or `undefined` entries will be passed as `null` type in WebView2. Otherwise if an invalid or unsupported
     * object is passed via this API, an exception will be thrown and the message will fail to post.
     */
    postMessageWithAdditionalObjects(message: any, additionalObjects: ArrayLike<any>): void;

使用示例

经测试，目前只支持前端的File类型，使用示例如下：

前端：

 <input id="file" type="file" value="选择文件" accept="*/*"/>

import {onMounted} from "vue";

onMounted(() => {
  const file = document.querySelector("#file") as HTMLInputElement | null;
  file?.addEventListener("change", () => {
    console.log(file.files);
    if (file.files != null) {
      window.chrome.webview.postMessageWithAdditionalObjects("files", file.files);//files的类型是 FileList
    }
  })
})

后端接收的方法：

#region 监听前端消息

webview.CoreWebView2.WebMessageReceived += CoreWebView2OnWebMessageReceived;

#endregion

private void CoreWebView2OnWebMessageReceived(object? sender, CoreWebView2WebMessageReceivedEventArgs e)
{
    var message = e.TryGetWebMessageAsString();
    var objs = e.AdditionalObjects;
    var a = e.Source;
    Debug.WriteLine(JsonSerializer.Serialize(objs[0]));
}

当前端选择一个图片时，前端打印选择的结果：

传递给后端，后端接收到的数据：

前端从file.files拿到的数据是没有路径的，传给后端后有了完整路径，是不是很神奇。