Created
March 3, 2014 19:38
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AsyncFormsDemo
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| using System; | |
| using System.Collections.Generic; | |
| using System.ComponentModel; | |
| using System.Data; | |
| using System.Drawing; | |
| using System.Linq; | |
| using System.Net; | |
| using System.Text; | |
| using System.Threading; | |
| using System.Threading.Tasks; | |
| using System.Windows.Forms; | |
| namespace AsyncPresoForms | |
| { | |
| public partial class Form1 : Form | |
| { | |
| private const string googleUrl = @"http://cnn.com/"; | |
| private const string ddgUrl = @"https://duckduckgo.com"; | |
| private readonly WebClient _client = new TimeoutWebClient(); | |
| public Form1() | |
| { | |
| InitializeComponent(); | |
| } | |
| private void button1_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // download two files serially - blocks the UI | |
| var result = _client.DownloadString(googleUrl).Substring(0, 100) + Environment.NewLine; | |
| result += _client.DownloadString(ddgUrl).Substring(0, 100); | |
| textBox1.Text = result; | |
| } | |
| private void button2_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // download two files serially using event/callback idiom | |
| // UI remains responsive | |
| var client2 = new WebClient(); | |
| _client.DownloadStringCompleted += (o, args) => | |
| { | |
| textBox1.Text = args.Result.Substring(0, 100); | |
| // what is this, javascript? | |
| client2.DownloadStringCompleted += (io, iargs) => textBox1.Text += args.Result.Substring(0, 100); | |
| client2.DownloadStringAsync(new Uri(ddgUrl)); | |
| }; | |
| // trigger the downloads | |
| _client.DownloadStringAsync(new Uri(googleUrl)); | |
| } | |
| private void button3_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // download two files serially using TPL | |
| // UI remains responsive | |
| var googleTask = Task.Run(() => _client.DownloadString(googleUrl)); | |
| var ddgTask = googleTask.ContinueWith((t) => | |
| { | |
| return t.Result.Substring(0, 100) + Environment.NewLine + _client.DownloadString(ddgUrl).Substring(0, 100); | |
| }); | |
| // could do more .ContinueWith here without deep nesting... | |
| textBox1.Text = ddgTask.Result; | |
| } | |
| private void button4_Click_1(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // download two files in parallel using TPL | |
| var client2 = new WebClient(); | |
| var googleTask = Task.Run(() => _client.DownloadString(googleUrl)); | |
| var ddgTask = Task.Run(() => client2.DownloadString(ddgUrl)); | |
| var completionTask = Task.WhenAll(new[] {googleTask, ddgTask}); | |
| // blocks the UI | |
| completionTask.Wait(); | |
| textBox1.Text = googleTask.Result.Substring(0, 100) + Environment.NewLine + ddgTask.Result.Substring(100); | |
| } | |
| // note: this is the only time it is appropriate to use async void... more on that later! | |
| private async void button5_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // download two files in parallel using await | |
| var client2 = new WebClient(); | |
| var googleTask = _client.DownloadStringTaskAsync(googleUrl); | |
| var ddgTask = client2.DownloadStringTaskAsync(ddgUrl); | |
| // no blocked UI! | |
| await Task.WhenAll(new[] { googleTask, ddgTask }); | |
| textBox1.Text = googleTask.Result.Substring(0, 100) + Environment.NewLine + ddgTask.Result.Substring(100); | |
| } | |
| private void button6_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| var task = Deadlock(true); | |
| // deadlocks! | |
| task.Wait(); | |
| textBox1.Text = task.Result; | |
| } | |
| private void button7_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| var task = Deadlock(false); | |
| // no deadlock! | |
| task.Wait(); | |
| textBox1.Text = task.Result; | |
| } | |
| private async Task<string> Deadlock(bool makeDeadlock) | |
| { | |
| if (makeDeadlock) | |
| await Task.Delay(1000); | |
| else | |
| await Task.Delay(1000).ConfigureAwait(false); | |
| return "Finished!"; | |
| } | |
| private async void button8_Click(object sender, EventArgs e) | |
| { | |
| textBox1.ResetText(); | |
| // the right way(note that false works here as well) | |
| textBox1.Text = await Deadlock(true); | |
| } | |
| private class TimeoutWebClient : WebClient | |
| { | |
| protected override WebRequest GetWebRequest(Uri address) | |
| { | |
| var req = base.GetWebRequest(address); | |
| req.Timeout = 3000; | |
| return req; | |
| } | |
| } | |
| } | |
| } |
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