1: public class InvocationConfirmationInteractiveChannelInitializer : IInteractiveChannelInitializer
3: public const string ConfirmMessage = "程序执行过程涉及到WCF服务调用，是否继续？";
4: public IAsyncResult BeginDisplayInitializationUI(IClientChannel channel, AsyncCallback callback, object state)
6: bool cancel = MessageBox.Show(ConfirmMessage, "WCF服务调用确认", MessageBoxButtons.YesNo) == DialogResult.No;
7: return new SimpleAsynsResult(cancel);
10: public void EndDisplayInitializationUI(IAsyncResult result)
11: {
12: SimpleAsynsResult asyncResult = (SimpleAsynsResult)result;
13: if((bool)asyncResult.AsyncState)
14: {
15: throw new InvocationCancelException("WCF服务调用被取消");
16: }
17: }
18: }
20: public class SimpleAsynsResult:IAsyncResult
21: {
22: public SimpleAsynsResult(object state)
23: {
24: this.AsyncState = state;
25: }
27: public object AsyncState { get; private set; }
28: public WaitHandle AsyncWaitHandle { get; private set; }
29: public bool CompletedSynchronously
30: {
31: get { return true; }
32: }
33: public bool IsCompleted
34: {
35: get { return true; }
36: }
37: }
我们通过一个自定义的ContractBehavior（InvocationConfirmationBehaviorAttribute ）将上面自定义的InvocationConfirmationInteractiveChannelInitializer应用到客户端运行时。如下面的代码片断所示，在实现的ApplyClientBehavior方法中，我们创建了一个InvocationConfirmationInteractiveChannelInitializer对象并将其添加到客户端运行时的InteractiveChannelInitializers集合中。
1: [AttributeUsage(AttributeTargets.Class | AttributeTargets.Interface)]
2: public class InvocationConfirmationBehaviorAttribute : Attribute, IContractBehavior
4: public void AddBindingParameters(ContractDescription contractDescription, ServiceEndpoint endpoint, BindingParameterCollection bindingParameters) { }
5: public void ApplyClientBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, ClientRuntime clientRuntime)
7: clientRuntime.InteractiveChannelInitializers.Add(new InvocationConfirmationInteractiveChannelInitializer());
9: public void ApplyDispatchBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, DispatchRuntime dispatchRuntime) { }
10: public void Validate(ContractDescription contractDescription, ServiceEndpoint endpoint) { }
11: }
以特性形式定义的InvocationConfirmationBehaviorAttribute直接以如下的方式直接应用到作为服务契约的ICalcualtor接口中：
1: [ServiceContract(Name = "CalculatorService", Namespace ="http://www.artech.com/")]
2: [InvocationConfirmationBehavior]
3: public interface ICalculator
5: [OperationContract]
6: double Add(double x, double y);
那么在进行服务调用的时候，确认对话框会自动弹出来。如果用户选择终止当前服务调用，那么InvocationCancelException异常会被抛出来，我们只需要捕捉该类型的异常即可。如下所示的是“=”按钮的Click事件代码：
1: public partial class Form1 : Form
3: //其他成员
4: private void buttonCalculate_Click(object sender, EventArgs e)
6: this.textBoxResult.Text = string.Empty;
7: using (ChannelFactory<ICalculator> channelfactory = new ChannelFactory<ICalculator>("calculatorservice"))
9: ICalculator calculator = channelfactory.CreateChannel();
10: try
11: {
12: double op1 = double.Parse(this.textBoxOp1.Text);
13: double op2 = double.Parse(this.textBoxOp2.Text);
14: double result = calculator.Add(op1,op2);
15: this.textBoxResult.Text = result.ToString();
16: }
17: catch (InvocationCancelException)
18: {
19: }
20: catch (Exception ex)
21: {
22: MessageBox.Show(ex.Message);
23: }
24: }
25: }
26: }
昨天有人在微博上问我如下一个问题："老蒋，客户端调用wcf的一个接口函数时，有没有什么办法可以先弹出一个确认框，确认后再执行调用。因为这个接口函数再很多地方都执行了调用，所以我想在某个入口进行统一地弹出一个确认框..."。其实这个问题可以通过WCF的扩展来完成，具体来说这个扩展涉及到一个我们不太常用的组件“InteractiveChannelInitializer”，在我的《WCF全面解析》中对它有过概括性的介绍。
