C＃-如何在异步方法调用后更新网页？

Question

I have a web page that has a form to add devices.

When a user adds a device, the device is registered in 4 different places. Since each of these 4 registrations takes time I decided to use asynchronous calls.

So, when the user clicks the save button an AJAx request is fired to the server and invokes the "Save" method. The "Save" method has a loop with an asynchronous call to the "Register" method, like this:

public delegate bool DeviceControllerAsync(...);

public static string Save(...)
{
    //Get all active controllers
    List<Controller> lstControllers = Controller.Get();
    foreach (Controller controller in lstControllers)
    {
        // Invoke asynchronous write method
        DeviceControllerAsync caller = new DeviceControllerAsync(ArubaBL.RegisterDevice);

        // Initiate the asychronous call.
        IAsyncResult result = caller.BeginInvoke(..., null, null);
    }
    return GetRegisteredDevices();
}

The problem here is that the "GetRegisteredDevices" call is pointless because the async methods haven't finished yet and there will be no devices to return. Also, I can't update the UI when these actions finish because the main method already returned to the UI.

(I'm ignoring the case here if the user moves the another page right after clicking the "Save" button.)

So, is there a way for me to know when all async calls finished and then invoke a method that will update the UI?

Answer 1

A simplified example of what this might look like using the TPL library and the async/await keywords.

public static async string Save(...)
{
    //Get all active controllers
    List<Controller> lstControllers = Controller.Get();

    //Create a task object for each async task
    List<Task<returnValueType>> controllerTasks = lstControllers.Select(controller=>{
        DeviceControllerAsync caller = new DeviceControllerAsync(ArubaBL.RegisterDevice);
        return Task.Factory.FromAsync<returnValueType>(caller.BeginInvoke, caller.EndInvoke, null);
    }).ToList();

    // wait for tasks to complete (asynchronously using await)
    await Task.WhenAll(controllerTasks);

    //Do something with the result value from the tasks within controllerTasks
}