Backgroundworker blocks UI

Question

I try to perform an easy task in an other backgroundthread, so the UI doesn't get blocked, but it still gets blocked. Did I forget anything?

public partial class backgroundWorkerForm : Form
{
    public backgroundWorkerForm()
    {
        InitializeComponent();
    }

    private void doWorkButton_Click(object sender, EventArgs e)
    {
        if (backgroundWorker.IsBusy != true)
        {
            // Start the asynchronous operation.
            backgroundWorker.RunWorkerAsync();
        }
    }

    private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        //BackgroundWorker worker = sender as BackgroundWorker;
        if (textBoxOutput.InvokeRequired)
        {
            textBoxOutput.Invoke(new MethodInvoker(delegate
            {
                for (int i = 0; i < 10000; i++)
                {
                    textBoxOutput.AppendText(i + Environment.NewLine);
                }
            }));
        }
    }
}

While the textBox gets filled, the UI is blocked:

Answer 1

Your invocation code should be outside the loop. Everything in the invoked codeblock, will be executed on the UI thread, thus blocking it.

    private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        //BackgroundWorker worker = sender as BackgroundWorker;
        for (int i = 0; i < 10000; i++)
        {
            // do long-running task

            //if (textBoxOutput.InvokeRequired)
            //{
                textBoxOutput.Invoke(new MethodInvoker(delegate
                {
                    textBoxOutput.AppendText(i + Environment.NewLine);
                }));
            //}
        }
    }