private async void LoadData_Click(Object sender, EventArgs e)
{
    this.LoadDataBtn.Enabled = false;

    IProgress<String> progressHandler = new Progress<String>(p => this.Log(p));

    this.Log("Initiating work...");

    List<Int32> result = await this.HeavyIO(new List<Int32> { 1, 2, 3 }, progressHandler);

    this.Log("Done!");

    this.LoadDataBtn.Enabled = true;
}

private async Task<List<Int32>> HeavyIO(List<Int32> ids, IProgress<String> progress)
{
    List<Int32> result = new List<Int32>();

    foreach (Int32 id in ids)
    {
        progress?.Report("Downloading data for " + id);

        await Task.Delay(500); // Assume that data is downloaded from the web here.

        progress?.Report("Data loaded successfully for " + id);

        Int32 x = id + 1; // Assume some lightweight processing based on downloaded data.

        progress?.Report("Processing succeeded for " + id);

        result.Add(x);
    }

    return result;
}

private void Log(String message)
{
    message += Environment.NewLine;
    this.RichTextBox.AppendText(message);
    Console.Write(message);
}

Initiating work...
Downloading data for 1
Data loaded successfully for 1
Processing succeeded for 1
Downloading data for 2
Data loaded successfully for 2
Processing succeeded for 2
Downloading data for 3
Done!
Data loaded successfully for 3
Processing succeeded for 3