I generally recommend Task and/or await if using .NET 4.5. But Task & BGW have 2 distinctly different scenarios. Task is good for general short asynchronous tasks that could be chained to a continuation and await is good at tasks implicitly marshalling back to the UI thread. BGW is good for a single long operation that shouldn't affect the responsiveness of your UI. You can drag-drop a BGW onto design surface and double-click to create event handlers. You don't have to deal with LongRunning or ConfigureAwait if you don't want to marshal to another thread. Many find BGW progress easier than IProgress<T>.
Here's some examples of using both in a "lengthy operation" scenario:
Since the question specifically mentions .NET 4.0, the following is simple code that uses a Task to do a lengthy operation while providing progress to a UI:
startButton.Enabled = false;
var task = Task.Factory.
StartNew(() =>
{
foreach (var x in Enumerable.Range(1, 10))
{
var progress = x*10;
Thread.Sleep(500); // fake work
BeginInvoke((Action) delegate {
progressBar1.Value = progress;
});
}
}, TaskCreationOptions.LongRunning)
.ContinueWith(t =>
{
startButton.Enabled = true;
progressBar1.Value = 0;
});
Similar code with BackgroundWorker might be:
startButton.Enabled = false;
BackgroundWorker bgw = new BackgroundWorker { WorkerReportsProgress = true };
bgw.ProgressChanged += (sender, args) =>
{ progressBar1.Value = args.ProgressPercentage; };
bgw.RunWorkerCompleted += (sender, args) =>
{
startButton.Enabled = true;
progressBar1.Value = 0;
};
bgw.DoWork += (sender, args) =>
{
foreach (var x in Enumerable.Range(1, 10))
{
Thread.Sleep(500);
((BackgroundWorker)sender).ReportProgress(x * 10);
}
};
bgw.RunWorkerAsync();
Now, if you were using .NET 4.5 you could use Progress<T> instead of the BeginInvoke call with Task. And since in 4.5, using await would likely be more readable:
startButton.Enabled = false;
var pr = new Progress<int>();
pr.ProgressChanged += (o, i) => progressBar1.Value = i;
await Task.Factory.
StartNew(() =>
{
foreach (var x in Enumerable.Range(1, 10))
{
Thread.Sleep(500); // fake work
((IProgress<int>) pr).Report(x*10);
}
}, TaskCreationOptions.LongRunning);
startButton.Enabled = true;
progressBar1.Value = 0;
Using Progress<T> means the code is not coupled to a specific UI framework (i.e. the call to BeginInvoke) in much the same way that BackgroundWorker facilitates decoupling from a specific UI framework. If you don't care, then you don't need to introduce the added complexity of using Progress<T>
As to LongRunning, as Stephen Toub says: "You'd typically only use LongRunning if you found through performance testing that not using it was causing long delays in the processing of other work" so, if you find you need to use it, then you use it--there's the added analysis or just the "complexity" of always adding the LongRunning parameter. Not using LongRunning means the thread pool thread used for the long running operation won't be usable for other, more transient, tasks and could force the thread pool to delay starting one of these transient tasks while it starts up another thread (at least a second).
There's no attributes in the framework that specifically say that BGW (or EAP, or APM) are deprecated. So, it's up to you to decide where and when any of these things are "obsolete". BGW in particular always had a very specific usage scenario that still applies to it. You have fairly decent alternatives in .NET 4.0 and 4.5; but I don't really think BGW is "obsolete".
I'm not saying always use BackgroundWorker, I'm just saying think before you automatically deprecate BackgroundWorker, in some cases it might be a better choice.
