APM之基于事件的异步模式（EAP）-2
EAP是针对Windows窗体开发提供的方便使用的异步模式，可以在IDE中可视化的设计和使用
// The System.Net.WebClient class supports the Event-based Asynchronous Pattern
WebClient wc = new WebClient();
// When a string completes downloading, the WebClient object raises the
// DownloadStringCompleted event which will invoke our ProcessString method
wc.DownloadStringCompleted += (s, e) =>
{
System.Windows.Forms.MessageBox.Show((e.Error != null) ? e.Error.Message : e.Result);
};
// Start the asynchronous operation (this is like calling a BeginXxx method)
wc.DownloadStringAsync(new Uri("http://Wintellect.com"));
.net有很多的类是这个模式
System.ComponentModel.Component-derived types
System.ComponentModel.BackgroundWorker
System.Media.SoundPlayer
System.Net.WebClient
System.Net.NetworkInformation.Ping
System.Windows.Forms.PictureBox (derived from Control)
System.Object-derived types
System.Net.Mail.SmtpClient
System.Deployment.Application.ApplicationDeployment
System.Deployment.Application.InPlaceHostingManager
System.Activities.WorkflowInvoker
System.ServiceModel.Activities.WorkflowControlClient
System.Net.PeerToPeer.PeerNameResolver
System.Net.PeerToPeer.Collaboration.ContactManager
System.Net.PeerToPeer.Collaboration.Peer
System.Net.PeerToPeer.Collaboration.PeerContact
System.Net.PeerToPeer.Collaboration.PeerNearMe
System.ServiceModel.Discovery.AnnouncementClient
System.ServiceModel.Discovery.DiscoveryClient
使用TaskCompletionSource将EAP转换为Task
// The System.Net.WebClient class supports the Event-based Asynchronous Pattern
WebClient wc = new WebClient();
// Create the TaskCompletionSource and its underlying Task object
var tcs = new TaskCompletionSource<String>();
// When a string completes downloading, the WebClient object raises the
// DownloadStringCompleted event which will invoke our ProcessString method
wc.DownloadStringCompleted += (sender, ea) =>
{
// This code always executes on the GUI thread; set the Task’s state
if (ea.Cancelled) tcs.SetCanceled();
else if (ea.Error != null) tcs.SetException(ea.Error);
else tcs.SetResult(ea.Result);
};
// Have the Task continue with this Task that shows the result in a message box
// NOTE: The TaskContinuationOptions.ExecuteSynchronously flag is required to have this code
// run on the GUI thread; without the flag, the code runs on a thread pool thread
tcs.Task.ContinueWith(t =>
{
try
{
System.Windows.Forms.MessageBox.Show(t.Result);
}
catch (AggregateException ae)
{
System.Windows.Forms.MessageBox.Show(ae.GetBaseException().Message);
}
}, TaskContinuationOptions.ExecuteSynchronously);
// Start the asynchronous operation (this is like calling a BeginXxx method)
wc.DownloadStringAsync(new Uri("http://Wintellect.com"));
APM之EAP APM比较、
|
|
优点 |
缺点 |
|
EAP |
可以和Visual Stuido配合使用，提供设计时支持 EAP是通过SynchronizationContext处理线程模型的，因此GUI程序中使用方便 |
比APM消耗的更多地内存、更慢的速度 EAP的异常不会抛出 |
|
APM |
APM更接近事物本质 EAP内部一般都是用APM事先 |
- |
详细参考：
Clr Via C#
