? web service实现原理与异步调用 收藏
??? net2.0环境下，Web service中的每个方法，在Client端添加引用后生成的代理类中都会产生相应的异步方法和结束事件。我们可以利用这个异步方法和事件，轻松实现异步调用web service.
??? 简单范例
??? 假设在web service中定义了一个数据查询的方法：
[WebMethod]
?? public DataSet ExecuteQuery(string SQL)
??????? {
??????????? using (OracleConnection conn = new OracleConnection(connstrSQL))
??????????? {
??????????????? try
??????????????? {
??????????????????? conn.Open();
??????????????????? OracleCommand cmd = new OracleCommand(sql,conn);
??????????????????? OracleDataAdapter ada = new OracleDataAdapter(cmd);
??????????????????? DataSet ds = new DataSet();
??????????????????? ada.Fill(ds);
??????????????????? return ds;
??????????????? }
??????????????? catch (OracleException ex)
??????????????? {
??????????????????? throw new Exception(ex.Message);
??????????????? }
??????????????? finally
??????????????? {
??????????????????? conn.Close();
??????????????? }
??????? }
??? 客户端：
///说明：
///panel1中放置了动态加载字样的图片等
///???
?public partial class frmStock : Form
??? {
??????? Service.MyService w = new Service.MyService(); //调用web service
??????? public frmStock()
??????? {
??????????? InitializeComponent();
??????? }
??????? private void frmStock_Load(object sender,EventArgs e)
??????? {
??????????? //添加异步方法执行后触发事件
??????????? w.ExecuteQueryCompleted += new WMS.ExecuteQueryCompletedEventHandler(w_ExecuteQueryCompleted);
??????? }
??????? private void btnFind_Click(object sender,EventArgs e)
??????? {
??????????? string sql = "select * from test";
???????????? w.ExecuteQueryAsync(sql);? //调用对应异步方法
???????????? ChangeStatus(true);
??????? }
??????? void w_ExecuteQueryCompleted(object sender,WMS.ExecuteQueryCompletedEventArgs e)
??????? {
?????????? DataTable dt= e.Result.Tables[0];? //获得执行结果 e
?????????? ChangeStatus(false);
?????????? if (dt.Rows.Count <= 0)
?????????? {
?????????????? MessageBox.Show("没有数据","information",MessageBoxButtons.OK,MessageBoxIcon.Information);
?????????????? return;
?????????? }
?????????? gvshow.AutoGenerateColumns = false;
?????????? gvshow.DataSource = dt;
??????? }
??????? private void btnExit_Click(object sender,EventArgs e)
??????? {
??????????? this.Close();
??????? }
??????? private void ChangeStatus(bool sign)
??????? {
??????????? panel1.Visible = sign;
????????????
??????? }
??? }
?? 这样,可以
??? 1.避免了假死现象
??? 2.可以提供友好的用户体验
???
??? 实现原理
??? web service 发布后，客户端添加引用，之后vs实际上在此时已经在后台生成本地代理类。之后看起来像是对web service的操作，实际上是对本地代理类的操作。代理类中处理网路访问逻辑，客户端的使用就象操作本地类一样简单便捷。
??? 客户端发出web service请求后，请求到达代理类，代理类处理请求从服务端获得SOAP数据包，而后进行数据处理后转发客户端。此中间涉及到的关于SOAP,WSDL等定义，简单的可以理解为：SOAP中定义了传输数据类型的格式和规则，而WSDL则以XML的形式定义了web service的消息和有关操作，通过http传输协议进行数据传输...
??? 那么代理类中到底如何定义的呢？
??? 我们可以通过自定义代理类的方式来分析代理类的详细信息。
??? 1.首先创建web service：Service.asmx
??? 2.IIS中建立虚拟目录并发布
??? 3.通过WSDL.exe工具生成代理类。
??? 打开SDK命令提示窗口,如下作业：
d:/Program Files/Microsoft Visual Studio 8/SDK/v2.0>wsdl http://localhost/Serve/Service.asmx?wsdl
Microsoft (R) Web Services Description Language Utility
[Microsoft (R) .NET Framework,Version 2.0.50727.42]
Copyright (C) Microsoft Corporation. All rights reserved.
Writing file 'd:/Program Files/Microsoft Visual Studio 8/SDK/v2.0/Service.cs'.
??? 其中service.cs就是生成的代理类，打开可见，其中涉及到异步方法，事件的生成。(部分代码如下)
?
?/// <remarks/>
??? public event HelloWorldCompletedEventHandler HelloWorldCompleted;
????
??? /// <remarks/>
??? public event showInfoCompletedEventHandler showInfoCompleted;
????
??? /// <remarks/>
??? [System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/HelloWorld",RequestNamespace="http://tempuri.org/",ResponseNamespace="http://tempuri.org/",Use=System.Web.Services.Description.SoapBindingUse.Literal,ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
??? public string HelloWorld() {
??????? object[] results = this.Invoke("HelloWorld",new object[0]);
??????? return ((string)(results[0]));
??? }
????
??? /// <remarks/>
??? public System.IAsyncResult BeginHelloWorld(System.AsyncCallback callback,object asyncState) {
??????? return this.BeginInvoke("HelloWorld",new object[0],callback,asyncState);
??? }
????
??? /// <remarks/>
??? public string EndHelloWorld(System.IAsyncResult asyncResult) {
??????? object[] results = this.EndInvoke(asyncResult);
??????? return ((string)(results[0]));
??? }
????
??? /// <remarks/>
??? public void HelloWorldAsync() {
??????? this.HelloWorldAsync(null);
??? }
????
??? /// <remarks/>
??? public void HelloWorldAsync(object userState) {
??????? if ((this.HelloWorldOperationCompleted == null)) {
??????????? this.HelloWorldOperationCompleted = new System.Threading.SendOrPostCallback(this.OnHelloWorldOperationCompleted);
??????? }
??????? this.InvokeAsync("HelloWorld",this.HelloWorldOperationCompleted,userState);
??? }
????
??? private void OnHelloWorldOperationCompleted(object arg) {
??????? if ((this.HelloWorldCompleted != null)) {
??????????? System.Web.Services.Protocols.InvokeCompletedEventArgs invokeArgs = ((System.Web.Services.Protocols.InvokeCompletedEventArgs)(arg));
??????????? this.HelloWorldCompleted(this,new HelloWorldCompletedEventArgs(invokeArgs.Results,invokeArgs.Error,invokeArgs.Cancelled,invokeArgs.UserState));
??????? }
??? }
????
??? /// <remarks/>
??? 4.通过csc命令把service.cs生成为dll文件
??? 5.在专案中添加对此dll的引用
??? 6.这样对此dll的应用实际上就是通过这个代理类访问我们发布的web service.
?
??? 设计模式的应用
??? 此种方式的实现，在设计模式中就是有名的“代理模式”的实现方式。
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转自！：http://blog.csdn.net/JustLovePro/archive/2008/08/27/2836898.aspx
