Async/await 调用 asmx 服务

Question

我正在使用 asmx 服务并尝试在尝试调用它时执行 async/await

目前我的控制器如下图

Public ActionResult Index()
{
   var data = _repository.GetDataFromAsmxService(somedata);
}

//RepositoryClass方法

public List<ObjectToReturn> GetDataFromAsmxService(somedata)
{
   var res = _asmxService.GetReportData(somedata);
   var result = process(res);
   return result;
}

进一步查看生成的 refrence.cs 文件后发现有用于等效调用的 void async 和 onCompleted 方法。

所以我改成了

        private void GetReportDataCallBack(object sender, GetReportDataCompletedEventArgs e)
        {
            var res = e.Result;
            var result = process(res);
        }

        public List<ObjectToReturn> GetDataFromAsmxService(somedata)
{
   _asmxService.GetReportDataCompleted +=GetReportDataCallBack;
   _asmxService.GetReportDataAsync(somedata);

}

但现在回调发生在事件委托上，所以我的控制器期望 return 数据不会得到它。 从控制器调用 async/await 并从 asmx webservice 获取数据的更好方法是什么

代码来自 Refenrece.cs //生成代码

[System.Web.Services.Protocols.SoapHeaderAttribute("ApiAuthenticationValue")]
        [System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://webservice.com/GetReportData", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Bare)]
        [return: System.Xml.Serialization.XmlElementAttribute(Namespace="http://webservice.com/")]
        public GetReportDataResponse GetReportData([System.Xml.Serialization.XmlElementAttribute(Namespace="http://webservice.com/")] GetReportDataRequest GetReportDataRequest) {
            object[] results = this.Invoke("GetReportData", new object[] {
                        GetReportDataRequest});
            return ((GetReportDataResponse)(results[0]));
        }

        /// <remarks/>
        public void GetReportDataAsync(GetReportDataRequest GetReportDataRequest) {
            this.GetReportDataAsync(GetReportDataRequest, null);
        }

        /// <remarks/>
        public void GetReportDataAsync(GetReportDataRequest GetReportDataRequest, object userState) {
            if ((this.GetReportDataOperationCompleted == null)) {
                this.GetReportDataOperationCompleted = new System.Threading.SendOrPostCallback(this.OnGetReportDataOperationCompleted);
            }
            this.InvokeAsync("GetReportData", new object[] {
                        GetReportDataRequest}, this.GetReportDataOperationCompleted, userState);
        }

        private void OnGetReportDataOperationCompleted(object arg) {
            if ((this.GetReportDataCompleted != null)) {
                System.Web.Services.Protocols.InvokeCompletedEventArgs invokeArgs = ((System.Web.Services.Protocols.InvokeCompletedEventArgs)(arg));
                this.GetReportDataCompleted(this, new GetReportDataCompletedEventArgs(invokeArgs.Results, invokeArgs.Error, invokeArgs.Cancelled, invokeArgs.UserState));
            }
        }

Answer 1

你拥有的是 Event-Based Asynchronous Pattern (EAP) and what you want to do is wrap that up in a task so you can await it. You do this via a TaskCompletionSource.

public async Task<List<ObjectToReturn>> GetDataFromAsmxServiceAsync(GetReportDataRequest somedata)
{
    var tcs = new TaskCompletionSource<GetReportDataResponse>();
    _asmxService.GetReportDataCompleted += GetReportDataCallBack;
    _asmxService.GetReportDataAsync(somedata, tcs); //we pass tcs in so it can be used from the callback.
    GetReportDataResponse res;
    try
    {
        res = await tcs.Task;
    }
    finally
    {
        //unsubscribe from the handler when done so we don't get a leak.
        _asmxService.GetReportDataCompleted -= GetReportDataCallBack;
    }

    var result = process(res);
    return result;
}

private void GetReportDataCallBack(object sender, GetReportDataCompletedEventArgs e)
{
    var tcs = (TaskCompletionSource<GetReportDataResponse>)e.UserState;
    if (e.Cancelled)
    {
        tcs.TrySetCanceled();
    }
    else if (e.Error != null)
    {
        tcs.TrySetException(e.Error);
    }
    else
    {
        tcs.TrySetResult(e.Result);
    }
}

您还需要将控制器更改为异步

public Task<ActionResult> IndexAsync()
{
    var data = await _repository.GetDataFromAsmxServiceAsync(somedata);
}

Here is a good article 解释了如何从同步 MVC 代码转换为异步 MVC 代码，并解释了为什么即使 Index 现在称为 IndexAsync 它仍然可以用作 Index 的控制器。

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