应用AOP简化WinForm的异步操作——PostSharp实现

起因从事WinForm的园友们一定经历过：当程序需要执行一个耗时的操作时，窗体进入假死状态，然后标题栏显示一个令用户绝望的“未响应”。不明真相的用户此时可能认为程序已死，强行关闭重启程序，然后重复这个噩梦。而通常此时程序实际上已经完成了一部分业务，造成数据丢失或者产生的结果与预期不一致。针对这个case，有很多方法来解决：Thread/ThreadPool/Control.Invoke/BackgroundWorker...下面以BackgroundWorker举例：假设程序现在要执行一个耗时的操作，为了不让用户肆意猛击界面，弹出一个带有loading动画的对话框block住主界面。我们把这个对话框命名为BlockDialog效果如下：实现的代码可能如下，DoWork方法用于执行业务，RunWorkerCompleted用于绑定数据、刷新界面：

var worker = new BackgroundWorker();
worker.DoWork += new DoWorkEventHandler(DoWork);
worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(RunWorkerCompleted);
worker.RunWorkerAsync();
dialog = new BlockDialog();
dialog.ShowDialog(this);

反复写这样的代码让人感到厌倦，而且当一个复杂的界面出现大篇类似的代码，会让业务逻辑淹没其中难以厘清。所以，我们想到了AOP，通过attribute标记方法。以下使用大名鼎鼎的PostSharp作为基础工具二次开发。尝试我期望的代码风格是这样的：

[WorkThread]
void DoBusinessWork(){

LoadData();

Binding();
}

[GuiThread]
void Binding(){

}

现在开始：定制拦截方法的拦截器，继承自PostSharp的 MethodInterceptionAspect类

//业务线程
public class WorkThreadAttribute : MethodInterceptionAspect
{
private IBlockDialog blockForm;

public override void OnInvoke(MethodInterceptionArgs args)
{
var worker = new BackgroundWorker();
worker.DoWork += new DoWorkEventHandler(worker_DoWork);
worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
worker.RunWorkerAsync(args);
blockForm = args.Instance as IBlockDialog;
if (blockForm != null)
{
blockForm.Block();
}
}

void worker_DoWork(object sender, DoWorkEventArgs e)
{
var args = e.Argument as MethodInterceptionArgs;
args.Invoke(args.Arguments);
}

void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (blockForm != null)
{
blockForm.UnBlock();
}
}

}

//GUI线程public class GuiThreadAttribute : MethodInterceptionAspect{public override void OnInvoke(MethodInterceptionArgs args){var main = (Form)args.Instance;if (main.InvokeRequired){main.BeginInvoke(new Action(args.Proceed));}else{args.Proceed();}}}

其中定义了一个接口IBlockDialog，为的是调用者可以自定义Block对话框

public interface IBlockDialog{void Block();void UnBlock();}

执行异步操作的Form需要实现此接口，它需要具有Block/Unblock的行为。简单地实现，它只需要组合BlockDialog，Show/Close对话框即可。

public class BaseForm : Form, IBlockDialog{private BlockDialog blockDialog;protected     BlockDialog BlockDialog{get{return blockDialog ?? (blockDialog = new BlockDialog());}}#region Implementation of IBlockDialogpublic void Block(){BlockDialog.ShowDialog(this);}public void UnBlock(){BlockDialog.Close();}public void ShowProcess(int percentage){BlockDialog.ShowProcess(percentage);}#endregion}

以上基本已经实现本文的目标，它能满足常用的下载数据并绑定展示的需求。

增强现在再提一个需求，我们经常需要上传或导入数据，希望在BlockDialog上加一个进度条。这时我们可以用到BackgroundWorker ReportProgress的特性。问题是：如何让拦截器知道业务线程执行的进度？暂且不论拦截器是如何得知的，首先，业务线程自己先要知道自己执行了百分之几，并且，它还得讲出来，不能闷闷唧唧的执行。为此，1、我们定义一个Reporter接口，它要求业务线程实时的set进度值，同时可能让拦截器get到这个进度值。

public interface IProcessReporter{int ProcessPercentage { get; set; }}

2、下面对BaseForm扩展，实现IProcessReporter

public class ProcessForm : BaseForm , IProcessReporter{

    public int ProcessPercentage{get;set;}　　　　

　　[WorkThread]　　private void DoWork()　　{　　　　　//循环　　　　　//报告进度　　　　　//ProcessPercentage = ?%;　　}}

3、让拦截器监听IProcessReporter.ProcessPercentage的变化

怎么监听呢，用Timer吗？

可以，但有延时。

那用Observer吧!

Interceptor:在ProcessObsever处登记它启用的BackgroundWorker和要监听的Form:IProcessReporterProcessForm:进度变化时在ProcessObsever处更新ProcessObsever:Form执行业务进度发生变化时，通知要监听它的BackgroundWorker3.1 ProcessObserver的实现

public  class ProcessObserver{private static readonly Dictionary<BackgroundWorker, IProcessReporter> pairs = new Dictionary<BackgroundWorker, IProcessReporter>();private static readonly Dictionary<IProcessReporter,int> process = new Dictionary<IProcessReporter, int>();private static readonly ProcessObserver instance = new ProcessObserver();private ProcessObserver(){}public static ProcessObserver Instance{get{return instance;}}public  void Add(BackgroundWorker worker, IProcessReporter reporter){if (!pairs.ContainsKey(worker)){pairs.Add(worker, reporter);if (process.ContainsKey(reporter)){worker.ReportProgress(process[reporter]);}}}public  void Remove(BackgroundWorker worker){if(!pairs.ContainsKey(worker)) return;if (process.ContainsKey(pairs[worker])){process.Remove(pairs[worker]);}pairs.Remove(worker);}public  void Update(IProcessReporter reporter){if(process.ContainsKey(reporter)) process[reporter] = reporter.ProcessPercentage;else{process.Add(reporter, reporter.ProcessPercentage);}foreach (var pair in pairs){if (pair.Value == reporter){ pair.Key.ReportProgress(reporter.ProcessPercentage);//找到对应的BackgroundWorker,刷新进度}}}}

3.2 修改拦截器 WorkThreadAttribute

public override void OnInvoke(MethodInterceptionArgs args){　　var worker = new BackgroundWorker();worker.DoWork += new DoWorkEventHandler(worker_DoWork);worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);

    　　　if (args.Instance is IProcessReporter)　　　　{　　　　 　　processReporter = args.Instance as IProcessReporter;　　　　　　ProcessObserver.Instance.Add(worker, processReporter);　　　　　　worker.WorkerReportsProgress = true;　　　　　　worker.ProgressChanged += new ProgressChangedEventHandler(worker_ProgressChanged);　　　　}  

        worker.RunWorkerAsync(args);blockForm = args.Instance as IBlockDialog;if (blockForm != null){blockForm.Block();}}

3.3 修改ProcessForm 对 IProcessReporter的实现，进度发生变化时更新到Observer

private int percentage;public int ProcessPercentage{get{ return percentage; }set {　　　　　　　　 if (percentage != value){　　ProcessObserver.Instance.Update(this);}percentage = value;}}