CallBack

参考资料：http://msdn.microsoft.com/en-us/library/ms178208(zh-cn).aspx
aspx.cs页继承ICallbackEventHandler接口，实现不经过回发而以编程方式实现客户端回调。以下是测试例子。

1。客户端注册CallBack事件：

aspx:

<script type="text/javascript">
function HTMLControlCallServerMethod()  //setp1
{
    var myParam = "myValue";
    <%= ClientScript.GetCallbackEventReference(this,"myParam", "ReceiveServerData",null)%>;
}
function ReceiveServerData(rtnValue)  //得到GetCallbackResult的返回值,setp4
{
    alert(rtnValue);
}
</script>
...
<button onclick="HTMLControlCallServerMethod()">CallServer</button>

aspx.cs:

private string CallBackValue = string.Empty;

string ICallbackEventHandler.GetCallbackResult()  //返回值给客户端,setp3
{
    return CallBackValue + ",GetCallbackResult_OK";
}

void ICallbackEventHandler.RaiseCallbackEvent(string eventArgument)  //接收GetCallbackEventReference的参数,setp2
{
    this.CallBackValue = eventArgument + ",RaiseCallbackEvent_OK";  //客户端定义的变量
}

2。客户端注册多个CallBack事件：

根据实际操作需要，可以单独step1和step4的函数。如果操作类似，可以共用一组函数：

aspx:

<script type="text/javascript">
function HTMLControlCallServerMethod(btn)  //setp1
{
    var myParm = btn.id;
    <%= ClientScript.GetCallbackEventReference(this,"myParm", "ReceiveServerData",null)%>;
}
function ReceiveServerData(rtnValue)  //得到GetCallbackResult的返回值,setp4
{
    alert(rtnValue);
}
</script>
...
<button id="btnOne" onclick="HTMLControlCallServerMethod(this)">CallServer</button>
<button id="btnTwo" onclick="HTMLControlCallServerMethod(this)">CallServer2</button>

aspx.cs:

private string CallBackValue = string.Empty;

string ICallbackEventHandler.GetCallbackResult()  //返回值给客户端,setp3
{
    return CallBackValue + ",GetCallbackResult";
}

void ICallbackEventHandler.RaiseCallbackEvent(string eventArgument)  //接收GetCallbackEventReference的参数,setp2
{
    if (eventArgument == "btnOne")  //区分客户端定义的变量
    {
        this.CallBackValue = "btnOne,RaiseCallbackEvent";  
    }
    if (eventArgument == "btnTwo")
    {
        this.CallBackValue = "btnTwo,RaiseCallbackEvent";
    }
}

3。服务器端注册CallBack事件：

aspx:

<script type="text/javascript">
function SetControlVale(a)  //a是服务器端返回的值
{
    document.getElementById("tbNow").value = a;  //设置tb的值为处理后的结果
}
</script>
...
 <asp:TextBox ID="tbNow" runat="server"></asp:TextBox>

 aspx.cs:

private string callbackResult = string.Empty;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsCallback)
    {
        string callbackMethod = ClientScript.GetCallbackEventReference(this, "document.getElementById('tbNow').value", "SetControlVale", null);
        tbNow.Attributes.Add("OnClick", callbackMethod);
        // OnClick="WebForm_DoCallback('__Page',document.getElementById('tbNow').value,SetControlVale,null,null,false)"  //最终的结果
        //          WebForm_DoCallback(eventTarget, eventArgument, eventCallback, context, errorCallback, useAsync)  //函数原型
    }
}

public string GetCallbackResult()
{
    return callbackResult + "OK";
}
public void RaiseCallbackEvent(string eventArgument)
{
    callbackResult = eventArgument + System.DateTime.Now.Millisecond;
}

 

4。实际例子：重构客户端显示

aspx:

<script type="text/javascript">
function getRblValue()  //取得选择项作为参数传给服务器端
{
    var result="";
    var obj = document.getElementById("rblNewsType");  //得到一个Table
    var radio= obj.getElementsByTagName("input");
    for(var i=0;i<radio.length;i++)
   {
      if(radio[i].checked)
      {
         result=radio[i].value;
      }
   }
   return result;
}
function FourStep(arg)
{
    document.getElementById('lbTest').innerHTML=arg;  //服务器端返回的数据
}
</script>
....
<%= DateTime.Now %>
<asp:RadioButtonList ID="rblNewsType" runat="server">
    <asp:ListItem Text="选项1" Value="选项1Value"></asp:ListItem>
    <asp:ListItem Text="选项2" Value="选项2Value"></asp:ListItem>
</asp:RadioButtonList>
<asp:Label ID="lbTest" runat="server">原来的字样</asp:Label>
<br />
<asp:Button ID="btnRefreshTiem" runat="server" Text="PostBack" />

aspx.cs:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsCallback)
    {
        rblNewsType.Attributes.Add("OnClick", ClientScript.GetCallbackEventReference(this, "getRblValue()", "FourStep", null));
        //因为是CallBack,参数值无法用rblNewsType.SelectedValue取得
    }
}

public string GetCallbackResult()
{
    return "被修改成：" + RenderControl(lbTest);
}
public void RaiseCallbackEvent(string eventArgument)  //接收step1的参数
{
    lbTest.Text = eventArgument;
}
private string RenderControl(Control control)  //重画控件
{
    StringWriter writer1 = new StringWriter(CultureInfo.InvariantCulture);
    HtmlTextWriter writer2 = new HtmlTextWriter(writer1);

    control.RenderControl(writer2);
    writer2.Flush();
    writer2.Close();

    return writer1.ToString();
}

注：验证用户名是否存在的例子 http://www.cnblogs.com/vipcjob/archive/2009/07/29/1534064.html Part6，做法类似（增加了错误处理）。