A templated PleaseWait button, and introduction to template controls

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1. Introduction

This article presents the construction of a templated ASP.NET control, working as a PleaseWait button. Using C# with ASP.NET 2.0, you will see how to create a templated control and add specific functionality.

Some times, you need to perform some time consuming tasks during, say, a button click event, when submitting your page. Some times, the form's validation can request some call to a database, or a remote call, Web Services ... To inform the user that the server is doing something time consuming, it's a good idea to display a waiting message.

I've seen some articles that re-create a button with added properties, that display a message. But the presentation never suits to me. So I decided to create a complete one, customizable with a template functionality.

2. The result to obtain

What I want to have is something like this in my ASP.NET page:

<Test:PleaseWaitButton ID="PWB" runat="server">
    <PleaseWaitMessageTemplate>
        <div style="width:500px;color:green;border:1px solid red;text-align:center">
            <div>Please wait a moment, </div>
            <div>we are checking your informations ...</div>
            <asp:Image runat="server" ImageUrl="wait.gif" />
        </div>
    </PleaseWaitMessageTemplate>
</Test:PleaseWaitButton>

Then, we have the button, and the place to define the graphic visualization of the please wait message.

To look like a real button, we need to define an event handler on the button click. We want to be able to customize the text of the button, with the Text property too.

In a form, usually we want to use ASP.NET validation. Then, the button needs to check this validation and define, if needed, a ValidationGroup property.

<Test:PleaseWaitButton ID="PWB" runat="server" 
         OnClick="ClickButton" ValidationGroup="myGroup" 
         Text="Please Click">
    <PleaseWaitMessageTemplate>
        <div style="width:500px;color:green;border:1px solid red;text-align:center">
            <div>Please wait a moment, </div>
            <div>we are checking your informations ...</div>
            <asp:Image runat="server" ImageUrl="wait.gif" />
        </div>
    </PleaseWaitMessageTemplate>
</Test:PleaseWaitButton>

3. Creating the template button

First, you have to inherit from Control and implement INamingContainer. You have to define the ParseChildren(true) attribute too.

[System.Security.Permissions.PermissionSet(
  System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
[ParseChildren(true)]
[DefaultProperty("Text")]
public class PleaseWaitButton : Control, INamingContainer
{
}

3.1. The ITemplate property

This is all you need: have a template property. PersistenceMode is used to tell the parser that the property persists as an inner property. TemplateContainer is unused here, it's for databinding typing.

private ITemplate _pleaseWaitMessageTemplate = null;

[Browsable(false), DefaultValue(null), 
    PersistenceMode(PersistenceMode.InnerProperty), 
    TemplateContainer(typeof(TemplateItem))]
public ITemplate PleaseWaitMessageTemplate
{
    get { return _pleaseWaitMessageTemplate; }
    set { _pleaseWaitMessageTemplate = value; }
}

We need to define a TemplateItemp class too.

// TemplateItem should implement INamingContainer
[ToolboxItem(false)]
public class TemplateItem : Control, INamingContainer
{
}

4.2. Creation of the controls

We'll override the CreateChildControls method to create a Panel that will contain our control. In this Panel, if the user defines a template, we instantiate it (as a TemplateItem). If no template is defined, we create a default LiteralControl with a default message.

And just after that, we add a button, with a Click handler defined, and with the Text property set to our Text property.

With CSS styles, we set the Panel to display none. The button, outside the panel, is always visible.

protected override void CreateChildControls()
{
    Controls.Clear();
    // Create an hidden panel
    Panel panelMessage = new Panel();
    panelMessage.Attributes["style"] = "display:none";
    if (PleaseWaitMessageTemplate != null)
    {
        // if a template is defined, use it
        TemplateItem templateItem = new TemplateItem();
        PleaseWaitMessageTemplate.InstantiateIn(templateItem);
        panelMessage.Controls.Add(templateItem);
    }
    else
    {
        // else, create a default ugly message
        panelMessage.Controls.Add(new LiteralControl("Plesae Wait ..."));
    }

    // Button is created with Text property
    // and a click handler
    Button boutonValidation = new Button();
    boutonValidation.Text = Text;
    boutonValidation.Click += b_Click;

    // Then add panel and button
    Controls.Add(panelMessage);
    Controls.Add(boutonValidation);
}

4.3. Creation of the properties

As seen, we need to hold a ValidationGroup property and a Text property. If no text is defined, we use the default "OK" value. We define a Click event too. To ensure control creation, let's override the Controls property and call EnsureChildControls() (that will call CreateChildControls, if needed).

[Bindable(true), Category("Behavior"), Description("Validation group")]
public string ValidationGroup
{
    get { return (string)ViewState["ValidationGroup"] ?? string.Empty; }
    set { ViewState["ValidationGroup"] = value; }
}

[Bindable(true), Category("Appearance"), 
  DefaultValue("OK"), Description("Button's text")]
public string Text
{
    get { return (string)ViewState["Text"] ?? "OK"; }
    set { ViewState["Text"] = value; }
}

private event EventHandler _clickHandler;
public event EventHandler Click
{
    add { _clickHandler += value; }
    remove { _clickHandler -= value; }
}

public override ControlCollection Controls
{
    get { EnsureChildControls(); return base.Controls; }
}

4.4. Validation

We have to ask for the validation of the page (with the Page.Validate method). If a ValidationGroup is defined, we ask for the validation of this group.

private void b_Click(object sender, EventArgs e)
{
    // manual validation
    if (!string.IsNullOrEmpty(ValidationGroup))
        Page.Validate(ValidationGroup);
    else
        Page.Validate();
    // Fire the user-define click event, if defined
    if (_clickHandler != null)
        _clickHandler(sender, e);
}

4.4. Client-side JavaScript

On the client-side, we have to do two things:

• Client validation
• And display/hide the please wait message

This is done with JavaScript. We will play with the display style of the panel (represented as a div in HTML), if validation is OK or NOK.

So let's add some JavaScript in the rendering phase, to call a specific JavaScript function on the client button click event (see comments).

But first, we have to find the clientId of the Panel.

protected override void OnPreRender(EventArgs e)
{
    // we look for the panel and set an ID
    // warning : this operation can't be done
    // in CreateChildControls, it would have been too earl
    Panel panelMessage = null;
    foreach (Control control in Controls)
    {
        if (control is Panel)
        {
            control.ID = ID + "_waiting";
            panelMessage = (Panel) control;
        }
    }
    // When panel founded, look for the button,
    // and add a clientside function 
    //(with panel clientId as parameters)
    if (panelMessage != null)
    {
        foreach (Control control in Controls)
        {
            if (control is Button)
            {
                ((Button) control).OnClientClick = 
                    string.Format("checkForm('{0}')", panelMessage.ClientID);
            }
        }
    }
    base.OnPreRender(e);
}

On render, create the java script functions that will manage the display, depending on the result of the client validation (client validation is done with the Page_ClientValidate method).

protected override void Render(HtmlTextWriter writer)
{
    // script client-side creation :
    // If there's a validation group,
    // call validation function with the group as parameters
    // else without parameters
    string validationGroupParameters = string.IsNullOrEmpty(ValidationGroup) ? 
            string.Empty : string.Format("'{0}'", ValidationGroup);

    // if validation is OK, display panel (and waiting message)
    // if validation NOK, hide panel and return false
    string script = @"function getObj(id)
{
    var o;
    if (document.getElementById)
    {
        o = document.getElementById(id).style;
    }
    else if (document.layers)
    {
        o = document.layers[id];
    }
    else if (document.all)
    {
        o = document.all[id].style;
    }
    return o;
}
function setDisplay(id)
{
    var o = getObj(id);
    if (o)
    {
        o.display = 'block';
    }
}
function unsetDisplay(id)
{
    var o = getObj(id);
    if (o)
    {
        o.display = 'none';
    }
}
function checkForm(divWaiting)
{
    try
    {
        if (!Page_ClientValidate(" + validationGroupParameters + @"))
        {
            unsetDisplay(divWaiting);
            return false;
        }
    }
    catch (e) {}
    setDisplay(divWaiting);
}";
    Page.ClientScript.RegisterStartupScript(GetType(), 
            "javascriptButton", script, true);

    base.Render(writer);
}

4. Create a default page that uses this button

4.1. With no validation

Just define the template control and the template property. Add if needed, a button click handler.

<Test:PleaseWaitButton ID="PWB" runat="server" OnClick="ClickButton">
    <PleaseWaitMessageTemplate>
        <div style="width:500px;color:green;border:1px solid red;text-align:center">
            <div>Please wait a moment, </div>
            <div>we are checking your informations ...</div>
            <asp:Image runat="server" ImageUrl="wait.gif" />
        </div>
    </PleaseWaitMessageTemplate>
</Test:PleaseWaitButton>

In the code-behind, simulate the time consuming task to perform ...

protected void ClickButton(object sender, EventArgs e)
{
    Thread.Sleep(2000);
}

4.2. With validation

4.2.1. Without validation group

Let's define a TextBox and add client-side validation with a RequiredFieldValidator control and server-side validation with a CustomValidator control.

<asp:TextBox runat="server" ID="aTextBox" />
<asp:RequiredFieldValidator runat="server" ControlToValidate="aTextBox" 
    ErrorMessage="Field should have a value" Display="dynamic"/>
<asp:CustomValidator runat="server" OnServerValidate="ValidateFunction" 
    Display="dynamic" ErrorMessage="Value should be ABC" />

protected void ClickButton(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        Thread.Sleep(2000);
        Response.Write("<br/>Informations are OK<br/>");
    }
}

protected void ValidateFunction(object source, ServerValidateEventArgs args)
{
    args.IsValid = aTextBox.Text == "ABC";
}

4.2.2. With validation group

You can try with a validation group too, like this:

<asp:TextBox runat="server" ID="aTextBox" />
<asp:RequiredFieldValidator runat="server" ControlToValidate="aTextBox"
    ErrorMessage="Field should have a value" 
    Display="dynamic" ValidationGroup="myGroup"/>
<asp:CustomValidator runat="server" OnServerValidate="ValidateFunction" 
    Display="dynamic" ErrorMessage="Value should be ABC" 
    ValidationGroup="myGroup"/>

<Test:PleaseWaitButton ID="PWB" runat="server" 
         OnClick="ClickButton" ValidationGroup="myGroup">
    <PleaseWaitMessageTemplate>
        <div style="width:500px;color:green;border:1px solid red;text-align:center">
            <div>Please wait a moment, </div>
            <div>we are checking your informations ...</div>
            <asp:Image runat="server" ImageUrl="wait.gif" />
        </div>
    </PleaseWaitMessageTemplate>
</Test:PleaseWaitButton>

protected void ClickButton(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        Thread.Sleep(2000);
        Response.Write("<br/>Informations are OK<br/>");
    }
}

protected void ValidateFunction(object source, ServerValidateEventArgs args)
{
    args.IsValid = aTextBox.Text == "ABC";
}

5. Preview

6. Conclusion

I hope you'll find this template button useful and maybe learn how to create a template control in ASP.NET with C#. Validation is a critical point and is very useful in an ASP.NET page. Knowing how to take advantage of validation with the validation API can be very powerful too.

If you see an error in this article, in the source code, or for any other information, send me a comment.

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