<%@ Page Language="C#" MasterPageFile="~/MsdnMag.master" 
    CompileWith="Default.aspx.cs" ClassName="Default_aspx" 
    Title="Cutting Edge (Jan05)" %>
<%@ Register TagPrefix="cc1" Namespace="MsdnMag.Controls"
    Assembly="CallbackControls" %>

<asp:Content Runat="server" ContentPlaceHolderID="PageDescription">
    <asp:Label Runat="Server" ID="Desc">Demonstrates controls that 
    implement client-side callback functionality</asp:Label>
</asp:Content>

<asp:Content Runat="server" ContentPlaceHolderID="PageBody">
    <h1>Register for a free account</h1>
    <table cellpadding="0"><tr>
            <td><b>User ID</b></td>
            <td><asp:TextBox ID="UserId" Runat="server" Text="dino" />
                <asp:CustomValidator ID="valUserId" Runat="Server" 
                    ControlToValidate="UserId" ValidateEmptyText="true" 
                    ErrorMessage="The user ID already exists or is empty"
                    OnServerValidate="EnsureUnique" Text="*" /></td>
        </tr>
        <tr>
            <td><b>Email address</b></td>
            <td><asp:TextBox ID="Email" Runat="server" />
                <asp:RegularExpressionValidator ID="valEmail" 
                   Runat="Server" ControlToValidate="Email" 
                   Text="*" ErrorMessage=
                   "The value does not appear to be a valid email address"
                   ValidationExpression=
                   "[a-zA-Z_0-9.-]+\@[a-zA-Z_0-9.-]+\.\w+" /></td>
        </tr>
        <tr>
            <td><b>Password</b></td>
            <td><asp:TextBox ID="Pswd" Runat="server" 
                   TextMode="Password" />
                <asp:CustomValidator ID="valPswd" Runat="Server" 
                    ControlToValidate="Pswd" 
                    Text="*" ErrorMessage="Enter a strong 
                        password (8+ chars including lower and 
                        upper case, digits and symbols"
                    OnServerValidate="EnsureStrong" /></td>
        </tr>
        <tr>
            <td bgcolor="lightyellow">
                <cc1:CallbackValidator 
                    ID="CallbackValidator1" Runat="server" 
                    ShowDetailedInfo="true" ButtonText="Validate" /></td>
            <td bgcolor="lightyellow" align="right">
                <asp:Button ID="Button1" Runat="server" 
                    Text="Submit" Font-Bold="True" /></td>
        </tr></table>
</asp:Content>

public class CallbackValidator : WebControl, 
    INamingContainer, ICallbackContainer, ICallbackEventHandler
{
    private StringCollection _controlsToValidate;

    [Description("The text to be shown on the button")]
    public string ButtonText
    {
        get { return Convert.ToString(ViewState["ButtonText"]); }
        set { ViewState["ButtonText"] = value; }
    }

    [Description("Whether to show the full validation error message")]
    public bool ShowDetailedInfo
    {
        get { return Convert.ToBoolean(ViewState["ShowDetailedInfo"]); }
        set { ViewState["ShowDetailedInfo"] = value; }
    }

    [Browsable(false)]
    public StringCollection ControlsToValidate
    {
        get {
            if (_controlsToValidate == null)
                _controlsToValidate = new StringCollection();
            return _controlsToValidate;
        }
    }

    protected override void CreateChildControls()
    {
        Controls.Clear();

        // Create the button to start the callback operation
        Button b = new Button();
        b.Text = ButtonText;
        b.CopyBaseAttributes(this);
        if (ControlStyleCreated)
            b.ApplyStyle(ControlStyle);

        // Attach some script code to trigger the remote call
        ICallbackContainer cont = this as ICallbackContainer;
        b.OnClientClick = cont.GetCallbackScript((IButtonControl) b, "");

        // Add the button to the control's hierarchy for display
        Controls.Add(b);

        // Inject any needed script code into the page
        EmbedScriptCode();
    }

    protected override void Render(HtmlTextWriter writer)
    {
        EnsureChildControls();
        base.Render(writer);
    }

    ...
}

public string GetCallbackScript(
    IButtonControl buttonControl, string argument)
{
    // Prepare the input for the server code
    int i = 0;
    StringBuilder sb = new StringBuilder("");
    foreach (string s in ControlsToValidate)
    {
        if (i>0) sb.Append("|");
        sb.Append(s);
        i++;
    }
    string args = String.Format("'{0}'", sb.ToString());
    string js = String.Format("javascript:{0};{1};{2}; return false;", 
        "__theFormPostData = ''",
        "WebForm_InitCallback()",
        Page.GetCallbackEventReference(
            this, args, "CallbackValidator_UpdateUI", "null"));
    return js;
}

public string RaiseCallbackEvent(string eventArgument)
{
    // Execute the server-side code
    // Receives a string like this:
    //     ctl|ctl|...ctl
    // Sends back a string like this:   
    //     ctl:valid:msg:tip|...ctl:valid:msg:tip
    StringBuilder sb = new StringBuilder("");
    string[] controlsToValidate = eventArgument.Split('|');
    int i = 0;
    foreach (string s in controlsToValidate)
    {
        BaseValidator val = NamingContainer.FindControl(s) 
            as BaseValidator;
        if (val != null)
        {
            val.Validate();
    
            if (i > 0) sb.AppendFormat("|");
            sb.AppendFormat("{0}:{1}:{2}:{3}",
                val.ClientID,
                (val.IsValid ? "1" : "0"),
                (val.IsValid ? "" : GetErrorText(val)),
                (val.IsValid ? "" : GetTooltip(val)));
        }
        i++;
    }

    return sb.ToString();
}

private void EmbedScriptCode()
{
    Assembly dll = Assembly.GetExecutingAssembly();
    StreamReader reader;
    reader = new StreamReader(dll.GetManifestResourceStream(
        "MsdnMag.CallbackValidator.js"));
    string js = reader.ReadToEnd();
    reader.Close();

    if (!Page.ClientScript.IsClientScriptBlockRegistered(
            "CallbackValidator"))
        Page.ClientScript.RegisterClientScriptBlock(
            typeof(CallbackValidator), "CallbackValidator", js, true);
}