update variable based upon results from .NET backgroundworker

I've got a C# program that talks to an instrument (spectrum analyzer) over a network. I need to be able to change a large number 开发者_JS百科of parameters in the instrument and read them back into my program. I want to use backgroundworker to do the actual talking to the instrument so that UI performance doesn't suffer.

The way this works is - 1) send command to the instrument with new parameter value, 2) read parameter back from the instrument so I can see what actually happened (for example, I try to set the center frequency above the max that the instrument will handle and it tells me what it will actually handle), and 3) update a program variable with the actual value received from the instrument.

Because there are quite a few parameters to be updated I'd like to use a generic routine. The part I can't seem to get my brain around is updating the variable in my code with what comes back from the instrument via backgroundworker. If I used a separate RunWorkerCompleted event for each parameter I could hardwire the update directly to the variable. I'd like to come up with a way of using a single routine that's capable of updating any of the variables. All I can come up with is passing a reference number (different for each parameter) and using a switch statement in the RunWorkerCompleted handler to direct the result. There has to be a better way.

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I think what I would do is pass a list of parameters, values, and delegates to the BackgroundWorker. That way you can write the assign-back code "synchronously" but have execution deferred until the values are actually retrieved.

Start with a "request" class that looks something like this:

class ParameterUpdate
{
    public ParameterUpdate(string name, string value, Action<string> callback)
    {
        this.Name = name;
        this.Value = value;
        this.Callback = callback;
    }

    public string Name { get; private set; }
    public string Value { get; set; }
    public Action<string> Callback { get; private set; }
}

Then write your async code to use this:

private void bwUpdateParameters_DoWork(object sender, DoWorkEventArgs e)
{
    var updates = (IEnumerable<ParameterUpdate>)e.Argument;
    foreach (var update in updates)
    {
        WriteDeviceParameter(update.Name, update.Value);
        update.Value = ReadDeviceParameter(update.Name);
    }
    e.Result = updates;
}

private void bwUpdateParameters_RunWorkerCompleted(object sender,
    RunWorkerCompletedEventArgs e)
{
    var updates = (IEnumerable<ParameterUpdate>)e.Argument;
    foreach (var update in updates)
    {
        if (update.Callback != null)
        {
            update.Callback(update.Value);
        }
    }
}

Here's how you would kick off the update. Let's say you've got a bunch of member fields that you want to update with the actual values of the parameters that were used:

// Members of the Form/Control class
private string bandwidth;
private string inputAttenuation;
private string averaging;

// Later on, in your "update" method
var updates = new List<ParameterUpdate>
{
    new ParameterUpdate("Bandwidth", "3000", v => bandwidth = v),
    new ParameterUpdate("InputAttenuation", "10", v => inputAttenuation = v),
    new ParameterUpdate("Averaging", "Logarithmic", v => averaging = v)
};
bwUpdateParameters.RunWorkerAsync(updates);

That's all you have to do. All of the actual work is done in the background, but you're writing simple variable-assignment statements as if they were in the foreground. The code is short, simple, and completely thread-safe because the actual assignments are executed in the RunWorkerCompleted event.

If you need to do more than this, such as update controls in addition to variables, it's very simple, you can put anything you want for the callback, i.e.:

new ParameterUpdate("Bandwidth", "3000", v =>
{
    bandwidth = v;
    txtBandwidth.Text = v;
})

Again, this will work because it's not actually getting executed until the work is completed.

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[Edit - look back at update history to see previous answer. Talk about not being able to see the wood for the trees]

Is there any reason that, rather than passing a reference number to the Background Worker, you can't pass the ID of the label that should be updated with any value passed back?

So the UI adds an item in the work queue containing:

• Variable to change
• Attempted change
• UI ID

and the BackgroundWorker triggers an event with EventArgs containing

• Attempted change
• Actual value after attempt
• UI ID
• Error Message (null if successful)

which is all the information you need to update your UI without a switch or multiple event args and without your Background Worker ever being aware of UI detail.

---

How about something like this?

[TestFixture]
public class BGWorkerTest
{
    string output1;
    string output2;

    [Test]
    public void DoTest()
    {
        var backgroundWorker = new BackgroundWorker();
        backgroundWorker.DoWork += (sender, args) =>
                                   {
                                       output1 = DoThing1();
                                       output2 = DoThing2();
                                   };
        backgroundWorker.RunWorkerAsync();
        //Wait for BG to finish
        Thread.Sleep(3000);
        Assert.AreEqual("Thing1",output1);
        Assert.AreEqual("Thing2",output2);
    }

    public string DoThing1()
    {
        Thread.Sleep(1000);
        return "Thing1";
    }
    public string DoThing2()
    {
        Thread.Sleep(1000);
        return "Thing2";
    }
}