AJAX - How to Pass value back to server

First time working with UpdatePanels in .NET.

I have an updatepanel with a trigger pointed to an event on a FormView control. The UpdatePanel holds a ListView with related data from a separate database.

When the UpdatePanel refreshes, it needs values from the FormView control so that on the server it can use them to query the database.

For the life if me, I can't figure out how to get those values. The event I'm triggering from has them, but I want the updatepanel to refresh asynchronously. How do I pass values to the load event on the panel?

Googled this ad nauseum and can't seem to get to an answer here. A link or an explanation would be immensely helpful..

Jeff

标签： asp.net-ajax asynchronous

3条回答

Rolldiameter

2楼-- · 2019-04-08 11:01

If you are working with an UpdatePanel just make sure that both controls are inside the panel and it will work as desired.

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爷的心禁止访问

3楼-- · 2019-04-08 11:07

make a javascript function that will collect the pieces of form data, and then sends that data to an ASHX handler. the ASHX handler will do some work, and can reply with a response.

This is an example I made that calls a database to populate a grid using AJAX calls. There are better libraries for doing AJAX (prototype, ExtJS, etc), but this is the raw deal. (I know this can be refactored to be even cleaner, but you can get the idea well enough)

Works like this...

User enters text in the search box,
User clicks search button,
JavaScript gets form data,
javascript makes ajax call to ASHX,
ASHX receives request,
ASHX queries database,
ASHX parses the response into JSON/Javascript array,
ASHX sends response,
Javascript receives response,
javascript Eval()'s response to object,
javascript iterates object properties and fills grid

The html will look like this...

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
    <script type="text/javascript" src="AjaxHelper.js"></script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="txtSearchValue" runat="server"></asp:TextBox>
        <input id="btnSearch" type="button" value="Search by partial full name" onclick="doSearch()"/>

        <igtbl:ultrawebgrid id="uwgUsers" runat="server" 
//infragistics grid crap
            </igtbl:ultrawebgrid>--%>
    </div>
    </form>
</body>
</html>

The script that fires on click will look like this...

//this is tied to the button click. It takes care of input cleanup and calling the AJAX method
function doSearch(){
    var eleVal; 
    var eleBtn;
    eleVal = document.getElementById('txtSearchValue').value;
    eleBtn = document.getElementById('btnSearch');
    eleVal = trim(eleVal);
    if (eleVal.length > 0) {
        eleBtn.value = 'Searching...';
        eleBtn.disabled = true;
        refreshGridData(eleVal);
    }
    else {
        alert("Please enter a value to search with. Unabated searches are not permitted.");
    }
}

//This is the function that will go out and get the data and call load the Grid on AJAX call 
//return.
function refreshGridData(searchString){

    if (searchString =='undefined'){
        searchString = "";
    }

    var xhr; 
    var gridData;
    var url;

    url = "DefaultHandler.ashx?partialUserFullName=" + escape(searchString);
    xhr = GetXMLHttpRequestObject();

    xhr.onreadystatechange = function() {
        if (xhr.readystate==4) {
            gridData = eval(xhr.responseText);
            if (gridData.length > 0) {
                //clear and fill the grid
                clearAndPopulateGrid(gridData);
            }
            else {
                //display appropriate message
            }
        } //if (xhr.readystate==4) {
    } //xhr.onreadystatechange = function() {

    xhr.open("GET", url, true);
    xhr.send(null);
}

//this does the grid clearing and population, and enables the search button when complete.
function clearAndPopulateGrid(jsonObject) {

    var grid = igtbl_getGridById('uwgUsers');
    var eleBtn;
    eleBtn = document.getElementById('btnSearch');

    //clear the rows
    for (x = grid.Rows.length; x >= 0; x--) {
        grid.Rows.remove(x, false);
    }

    //add the new ones
    for (x = 0; x < jsonObject.length; x++) {
        var newRow = igtbl_addNew(grid.Id, 0, false, false);
        //the cells should not be referenced by index value, so a name lookup should be implemented
        newRow.getCell(0).setValue(jsonObject[x][1]); 
        newRow.getCell(1).setValue(jsonObject[x][2]);
        newRow.getCell(2).setValue(jsonObject[x][3]);
    }

    grid = null;

    eleBtn.disabled = false;
    eleBtn.value = "Search by partial full name";
}


// this function will return the XMLHttpRequest Object for the current browser
function GetXMLHttpRequestObject() {

    var XHR; //the object to return
    var ua = navigator.userAgent.toLowerCase(); //gets the useragent text
    try
    {
        //determine the browser type
        if (!window.ActiveXObject)
        { //Non IE Browsers
            XHR = new XMLHttpRequest(); 
        }
        else 
        {
            if (ua.indexOf('msie 5') == -1)
            { //IE 5.x
                XHR = new ActiveXObject("Msxml2.XMLHTTP");
            }
            else
            { //IE 6.x and up  
                XHR = new ActiveXObject("Microsoft.XMLHTTP");   
            }
        } //end if (!window.ActiveXObject)

        if (XHR == null)
        {
            throw "Unable to instantiate the XMLHTTPRequest object.";
        }
    }
    catch (e)
    {
        alert("This browser does not appear to support AJAX functionality. error: " + e.name
              + " description: " + e.message);
    }
    return XHR;
} //end function GetXMLHttpRequestObject()

function trim(stringToTrim){
    return stringToTrim.replace(/^\s\s*/, '').replace(/\s\s*$/, '');
}

And the ashx handler looks like this....

Imports System.Web
Imports System.Web.Services
Imports System.Data
Imports System.Data.SqlClient

Public Class DefaultHandler
    Implements System.Web.IHttpHandler

    Private Const CONN_STRING As String = "Data Source=;Initial Catalog=;User ID=;Password=;"

    Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest

        context.Response.ContentType = "text/plain"
        context.Response.Expires = -1

        Dim strPartialUserName As String
        Dim strReturnValue As String = String.Empty

        If context.Request.QueryString("partialUserFullName") Is Nothing = False Then
            strPartialUserName = context.Request.QueryString("partialUserFullName").ToString()

            If String.IsNullOrEmpty(strPartialUserName) = False Then
                strReturnValue = SearchAndReturnJSResult(strPartialUserName)
            End If
        End If

        context.Response.Write(strReturnValue)

    End Sub


    Private Function SearchAndReturnJSResult(ByVal partialUserName As String) As String

        Dim strReturnValue As New StringBuilder()
        Dim conn As SqlConnection
        Dim strSQL As New StringBuilder()
        Dim objParam As SqlParameter
        Dim da As SqlDataAdapter
        Dim ds As New DataSet()
        Dim dr As DataRow

        'define sql
        strSQL.Append(" SELECT ")
        strSQL.Append("     [id] ")
        strSQL.Append("     ,([first_name] + ' ' + [last_name]) ")
        strSQL.Append("     ,[email] ")
        strSQL.Append(" FROM [person] (NOLOCK) ")
        strSQL.Append(" WHERE [last_name] LIKE @lastName")

        'clean up the partial user name for use in a like search
        If partialUserName.EndsWith("%", StringComparison.InvariantCultureIgnoreCase) = False Then
            partialUserName = partialUserName & "%"
        End If

        If partialUserName.StartsWith("%", StringComparison.InvariantCultureIgnoreCase) = False Then
            partialUserName = partialUserName.Insert(0, "%")
        End If

        'create the oledb parameter... parameterized queries perform far better on repeatable
        'operations
        objParam = New SqlParameter("@lastName", SqlDbType.VarChar, 100)
        objParam.Value = partialUserName

        conn = New SqlConnection(CONN_STRING)
        da = New SqlDataAdapter(strSQL.ToString(), conn)
        da.SelectCommand.Parameters.Add(objParam)

        Try 'to get a dataset. 
            da.Fill(ds)
        Catch sqlex As SqlException
            'Throw an appropriate exception if you can add details that will help understand the problem.
            Throw New DataException("Unable to retrieve the results from the user search.", sqlex)
        Finally
            If conn.State = ConnectionState.Open Then
                conn.Close()
            End If
            conn.Dispose()
            da.Dispose()
        End Try

        'make sure we have a return value
        If ds Is Nothing OrElse ds.Tables(0) Is Nothing OrElse ds.Tables(0).Rows.Count <= 0 Then
            Return String.Empty
        End If

        'This converts the table into JS array. 
        strReturnValue.Append("[")

        For Each dr In ds.Tables(0).Rows
            strReturnValue.Append("['" & CStr(dr("username")) & "','" & CStr(dr("userfullname")) & "','" & CStr(dr("useremail")) & "'],")
        Next

        strReturnValue.Remove(strReturnValue.Length - 1, 1)
        strReturnValue.Append("]")

        'de-allocate what can be deallocated. Setting to Nothing for smaller types may
        'incur performance hit because of a forced allocation to nothing before they are deallocated
        'by garbage collection.
        ds.Dispose()
        strSQL.Length = 0

        Return strReturnValue.ToString()

    End Function


    ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
        Get
            Return False
        End Get
    End Property

End Class

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萌系小妹纸

4楼-- · 2019-04-08 11:14

Try

...looking in the Request and Response.
...setting a breakpoint on the Load() method and query Me or this in the watch or immediate window to see if the values you want are maybe just not where you are expecting them?
...Put a (For Each ctl as Control in Me/This.Controls) and inspecting each control that is iterated and see if you are even getting the controls you expect.
... its not in Sender or EventArgs?

Try NOT using Update panels.... They can often cause more trouble than they are worth. It may be faster and less headache to use regular AJAX to get it done.

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AJAX - How to Pass value back to server

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