C# – How to get feedback to a page from a running thread in ASP.NET

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So I have this interface that is just one big GO button that syncs a bunch of data from one tool to another. The problem is it takes a really long freaking time and some users are left wondering whats the deal. So I am wondering if there is a way that I can put something in my loop so that every so many entries it sends something back to the page to update them on the progress.

Currently it is just an .aspx page with an aspx.cs behind it. The Go button fires off the whole process and it calls Response.Write a ton of times (as well as writing the same thing to a log file I made) but the Responses don't show until the entire thing is done.

Please advise.

Best Answer

You could design a class which will be stored in the session and which will represent the current state of the operation:

public class OperationState
{
    public object Result { get; set; }
    public int Progress { get; set; }
    public string Error { get; set; }
}

An instance of this class could be created when you start the operation and store it in the user session. Then at each step of the operation you could retrieve it from session and update the progress property. Once the operation terminates you could set the Result property or the Error property in case an exception occurs. In the meantime you could design a PageMethod which will be accessible from client script. This method will simply return the State instance from the session. You will then invoke it periodically and asynchronously from javascript to check the progress and update the DOM to notify the user.

Related Solutions

C# – How to get the index of the current iteration of a foreach loop

Ian Mercer posted a similar solution as this on Phil Haack's blog:

foreach (var item in Model.Select((value, i) => new { i, value }))
{
    var value = item.value;
    var index = item.i;
}

This gets you the item (item.value) and its index (item.i) by using this overload of LINQ's Select:

the second parameter of the function [inside Select] represents the index of the source element.

The new { i, value } is creating a new anonymous object.

Heap allocations can be avoided by using ValueTuple if you're using C# 7.0 or later:

foreach (var item in Model.Select((value, i) => ( value, i )))
{
    var value = item.value;
    var index = item.i;
}

You can also eliminate the item. by using automatic destructuring:

<ol>
foreach ((MyType value, Int32 i) in Model.Select((value, i) => ( value, i )))
{
    <li id="item_@i">@value</li>
}
</ol>

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

As per Prerak K's update comment (since deleted):

I guess I have not presented the question properly.

Situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.

So only accessing the value so that corresponding data can be fetched from the database.

The solution you want then should look like:

UserContrl1_LOadDataMethod()
{
    string name = "";
    if(textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.text; }));
    }
    if(name == "MyName")
    {
        // do whatever
    }
}

Do your serious processing in the separate thread before you attempt to switch back to the control's thread. For example:

UserContrl1_LOadDataMethod()
{
    if(textbox1.text=="MyName") //<<======Now it wont give exception**
    {
        //Load data correspondin to "MyName"
        //Populate a globale variable List<string> which will be
        //bound to grid at some later stage
        if(InvokeRequired)
        {
            // after we've done all the processing, 
            this.Invoke(new MethodInvoker(delegate {
                // load the control with the appropriate data
            }));
            return;
        }
    }
}

Best Answer

Related Solutions

C# – How to get the index of the current iteration of a foreach loop

C# – Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

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