DotNetBrowser 和承诺

Question

我在 .Net 应用程序中使用 DotNetBrowser 作为一种无头 Javascript 引擎。似乎 DotNetBrowser 不支持 Promises，或者我没有正确使用它们。

在 JS 中：

window.fooAsyncMethod = () => {
    return new Promise((resolve, reject) => {
        resolve('async value to resolve');
    });
}

在 C# 中：

var result = await browser.MainFrame.ExecuteJavascript("await window.fooAsyncMethod()")

在这种情况下，结果始终为空。我也尝试过 async/await，但总是收到 null：

window.fooAsyncMethod = async () => {
    return await someOtherAsyncMethod()
}

DotNetBrowser 是否支持运行异步 javascript？如果是这样，我如何才能等待异步操作的结果并在 C# 中解析该值？

Answer 1

查看JS-.NET bridge examples，它似乎是does support promises，但使用起来有点复杂。

如果您在 C# 端实现一种类型的 Promise 对象：

public static class JsObjectExtensions
{
    #region Methods

    public static JsPromise AsPromise(this IJsObject jsObject) => JsPromise.AsPromise(jsObject);

    #endregion
}

public sealed class JsPromise
{
    private readonly IJsObject jsObject;

    #region Constructors

    private JsPromise(IJsObject jsObject)
    {
        this.jsObject = jsObject;
    }

    #endregion

    public static JsPromise AsPromise(IJsObject jsObject) => !IsPromise(jsObject) ? null : new JsPromise(jsObject);

    public JsPromise Catch(Func<object, object> onRejected)
    {
        IJsObject newPromise = jsObject.Invoke("catch", onRejected) as IJsObject;
        return new JsPromise(newPromise);
    }

    public Task<Result> ResolveAsync()
    {
        TaskCompletionSource<Result> promiseTcs = new TaskCompletionSource<Result>();
        Then(obj => { promiseTcs.TrySetResult(Fulfilled(obj)); },
             obj => { promiseTcs.TrySetResult(Rejected(obj)); });

        promiseTcs.Task.ConfigureAwait(false);
        return promiseTcs.Task;
    }

    public void Then(Action<object> onFulfilled, Action<object> onRejected = null)
    {
        jsObject.Invoke("then", onFulfilled, onRejected);
    }

    public JsPromise Then(Func<object, object> onFulfilled, Func<object, object> onRejected = null)
    {
        IJsObject newPromise = jsObject.Invoke("then", onFulfilled, onRejected) as IJsObject;
        return new JsPromise(newPromise);
    }

    private Result Fulfilled(object o) => new Result(ResultState.Fulfilled, o);

    private static bool IsPromise(IJsObject jsObject)
    {
        if (jsObject == null || jsObject.IsDisposed)
        {
            return false;
        }

        IJsObject promisePrototype = jsObject.Frame.ExecuteJavaScript<IJsObject>("Promise.prototype").Result;
        return promisePrototype.Invoke<bool>("isPrototypeOf", jsObject);
    }

    private Result Rejected(object o) => new Result(ResultState.Rejected, o);

    public enum ResultState
    {
        Fulfilled,
        Rejected
    }

    public class Result
    {
        public object Data { get; }
        public ResultState State { get; }

        internal Result(ResultState state, object data)
        {
            State = state;
            Data = data;
        }
    }
}

然后你就可以像这样调用promise了：

                    IJsObject window = browser.MainFrame.ExecuteJavaScript<IJsObject>("window").Result;
                    //Prepare promise handlers
                    Action<object> promiseResolvedHandler = o => Console.WriteLine("Success: " + o);
                    Action<object> promiseRejectedHandler = o => Console.Error.WriteLine("Error: " + o);

                    //Create a promise that is fulfilled
                    Console.WriteLine("Create a promise that is fulfilled...");
                    IJsObject promise1 = window.Invoke<IJsObject>("CreatePromise", true);
                    //Append fulfillment and rejection handlers to the promise
                    promise1.Invoke("then", promiseResolvedHandler, promiseRejectedHandler);

                    //Create a promise that is rejected
                    Console.WriteLine("Create a promise that is rejected...");
                    IJsObject promise2 = window.Invoke<IJsObject>("CreatePromise", false);
                    //Append fulfillment and rejection handlers to the promise
                    promise2.Invoke("then", promiseResolvedHandler, promiseRejectedHandler);

                    CreatePromiseAsync(window).Wait();

请注意，以上所有代码均直接取自他们的Promises Example。