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Chapter 17: BackgroundWorker

Syntax

• bgWorker.CancellationPending //returns whether the bgWorker was cancelled during its
operation

• bgWorker.IsBusy //returns true if the bgWorker is in the middle of an operation

• bgWorker.ReportProgress(int x) //Reports a change in progress. Raises the "ProgressChanged"
event

• bgWorker.RunWorkerAsync() //Starts the BackgroundWorker by raising the "DoWork" event

• bgWorker.CancelAsync() //instructs the BackgroundWorker to stop after the completion of a
task.

Remarks

Performing long-running operations within the UI thread can cause your application to become
unresponsive, appearing to the user that it has stopped working. It is preferred that these tasks be
run on a background thread. Once complete, the UI can be updated.

Making changes to the UI during the BackgroundWorker's operation requires invoking the
changes to the UI thread, typically by using the Control.Invoke method on the control you are
updating. Neglecting to do so will cause your program to throw an exception.

The BackgroundWorker is typically only used in Windows Forms applications. In WPF
applications, Tasks are used to offload work onto background threads (possibly in combination
with async/await). Marshalling updates onto the UI thread is typically done automatically, when the
property being updated implements INotifyPropertyChanged, or manually by using the UI thread's
Dispatcher.

Examples

Assigning Event Handlers to a BackgroundWorker

Once the instance of the BackgroundWorker has been declared, it must be given properties and
event handlers for the tasks it performs.

/* This is the backgroundworker's "DoWork" event handler. This
method is what will contain all the work you
wish to have your program perform without blocking the UI. */

bgWorker.DoWork += bgWorker_DoWork;

/*This is how the DoWork event method signature looks like:*/
private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{

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