Client CallBack實作

2009-05-21

27039
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Asp.Net

Client CallBack的練習

步驟一: 實作 ICallbackEventHandler 介面
在vb中 Implements System.Web.UI.IcallbackEventHandler後，VS會自動產生以下2段程式

'實作 GetCallbackResult 方法，這個方法會被叫用，以便在伺服器上執行回呼

Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult

End Function

'實作 RaiseCallbackEvent方法，這個方法會將回呼結果傳回給用戶端

Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent

End Sub

步驟二:於Page_Load註冊JavaScript(網頁程式與後端程式的橋樑)

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim cbReference As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "ReceiveServerData", "context")

Dim callbackScript As String = "function CallServer(arg,context){" + cbReference + "}"

'若未註冊過CallServer，則註冊

If (Not Page.ClientScript.IsClientScriptBlockRegistered(Me.GetType, "CallServer")) Then

Page.ClientScript.RegisterClientScriptBlock(Me.GetType, "CallServer", callbackScript, True)

End If

End Sub
步驟三:編寫GetCallbackResult 方法及RaiseCallbackEvent方法

步驟三:編寫GetCallbackResult 方法及RaiseCallbackEvent方法

Protected txtUserInfo As String '使用者資訊

Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult

Return txtUserInfo

End Function

Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent

If (Not eventArgument Is Nothing) Then

Dim conn As New SqlConnection(ConnectionString)

Dim cmd As SqlCommand = conn.CreateCommand

cmd.CommandText = "Select top 1 User_ID From User_Data Where User_Name Like '%'+@User_Name+'%'"

cmd.Parameters.AddWithValue("@User_Name", eventArgument)

Try

conn.Open()

Dim dr As SqlDataReader = cmd.ExecuteReader

If dr.Read Then

txtUserInfo += "編號為:" + dr("User_ID").ToString.Trim

Else

If String.IsNullOrEmpty(eventArgument) Then

txtUserInfo = "姓名??"

Else

txtUserInfo = "無此人"

End If

dr.Close()

Catch ex As Exception

MyBase.Msg(ex.ToString)

Finally

conn.Dispose()

End Try

End If

End Sub

步驟四:編寫網頁

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="testCallBack.aspx.vb" Inherits="Lab_testCallBack" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>testCallBack</title>

</head>

function DoSearch() {

var txtFirstName = document.getElementById("txtUserName");

CallServer(txtFirstName.value, "");

}

function ReceiveServerData(arg,context) {

Results.innerText = arg ;

}

//setInterval('DoSearch()', 1000);

</script>

<body>

<div>

使用者<asp:TextBox ID="txtUserName" runat="server" ></asp:TextBox><asp:Button ID="Button1"

runat="server" Text="Button" OnClientClick="DoSearch();return false;" />

</div>

</form>

</body>

</html>

觀察結果
1.實作了ICallbackEventHandler，所以在網頁中出現了以下JavaScript
<script type="text/javascript">
//<![CDATA[
WebForm_InitCallback();//]]>
</script>
2.在Page_Load中註冊的程式碼如下
<script type="text/javascript">
//<![CDATA[
function CallServer(arg,context){WebForm_DoCallback('__Page',arg,ReceiveServerData,context,null,false)}//]]>
</script>
所以當按鍵點擊後，會呼叫JavaScript:DoSearch()
，然後再呼叫Page_Load中註冊的程式CallServer(arg,context)
，然後回到後端觸發RaiseCallbackEvent事件
，事件處理完後，再執行GetCallbackResult，將資料回傳至網頁JavaScript:ReceiveServerData(arg,context)
，注意，為什麼後端會知道要將程式回傳給ReceiveServerData(arg,context)呢?
原因就在Page_Load中註冊的程式碼中=> Dim cbReference As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "ReceiveServerData", "context")

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