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How to Check if ListBox is Empty on Client-Side

I created a javascript confirm as below.
<script Type="Text/Javascript">
function CheckListBox(lvi)
{
if(lvi == "")
{
if(confirm("Are you sure?"))
{
return true;
}
else
{
return false;
}
}
}
</script>
I need to test if the ListBox.Items control is empty... I already made reference on my aspx page
<script language="javascript" type="text/javascript" src="/JS/confirm.js"></script>
I want to know how to call it on my aspx.cs page . . . So I can pass the parameter:
string oi = Listbox_Clubes.Items.Count.ToString();//Its the parameter I want to pass

See this link for how to execute javascript from code behind
protected void Page_Load(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this, this.GetType(), Guid.NewGuid().ToString(), "CheckListBox(" + Listbox_Clubes.Items.Count.ToString() + ");", false);
}
Note: you must add a ScriptManager control in aspx page.

For your javascript, you can get the value without the code-behind (this assumes the script code is in the same page, in order to get the client ID):
<script>
function ClickListBox() {
if ($("#<%= Listbox_Clubes.ClientID %>").val() === null) {
if (confirm("Are you sure?")) {
return true;
}
else {
return false;
}
}
}
</script>
Similarly, you don't use javascript to validate on the server side. The code you posted will return all items in the ListBox. Here is one way to get the count of the number of selected items (I'm using .ToString() based on the OP code example):
string oi = Listbox_Clubes.Items.Cast<ListItem>().Where(i => i.Selected).Count().ToString();
However, there is no reason why you would get this value and pass it back to the client-side to do validation (what it sounds like you want to do in your post). Mainly because this involves a post-back, and client-side validation, by its nature, should occur before post-back. Also, you will still need to do server-side validation, even when you have client-side validation.
Related: in the code-behind, you can test to see if anything is selected by:
bool hasValue = Listbox_Clubes.SelectedItem != null;
The .SelectedItem returns the selected item with the lowest index in the list control. When nothing is selected, this value is null... so you know if the value isn't null, then at least one item was selected.
If you want to require that they choose at least one item, you can use a RequireFieldValidator and let that handle both validations. If you haven't done much with ASP.NET validators, that would be one good thing to read up on.
It sounds like you probably should read more about client-side validation and server-side validation and how to use them... because it seems like you are mixing them up.
The count code is a modified version of code in ASP:ListBox Get Selected Items - One Liner?

aspx change focus from different TextBoxes on the fly

I am trying to change the focus from one textbox to another while the character count in
on textbox reaches 13 I am using the code below with nothing happening whatsoever:
if (!this.ClientScript.IsClientScriptBlockRegistered("qtyFocus"))
{
this.ClientScript.RegisterClientScriptBlock(this.GetType(), "qtyFocus",
#"<script type='text/javascript' language='javascript'>function qtyFocus(){
var trckNumberLength = document.getElementById('txtTrackingNumber').value.length;
if(trckNumberLength == 13){
document.getElementById('txtQuantity').focus();
}}</script>");
}
txtTrackingNumber.Attributes.Add("onchange", "javascript:return qtyFocus();");
can anyone help please ?

Probably because the line in the script that's doing
var trckNumberLength = document.getElementById('txtTrackingNumber').value.length;
Needs to be changed for:
var trckNumberLength = document.getElementById('"+txtTrackingNumber.ClientID+"').value.length;
The reason being that txtTrackingNumber will very likely have a different Id when it's rendered on the page so you need to use the ClientID property of the control instead of the id you defined on the markup.

Storing an List<int> in viewstate

I have an aspx page which has the following:
A repeater with a linkbutton in each
The link button has a commandargument of an integer value
A user control
The idea is that when the user clicks on the linkbutton the value of the commandarguement is stored in a List. No problem you may think, however I need the value to be stored in an List in the usercontrol, not in the ASPX page. The List needs to be persisted across postbacks, so it also needs to be stored in the viewstate.
So I created a public property in the user control like so:
public List<int> ImageString {
get {
if (this.ViewState["ImageString"] != null) {
return (List<int>)(this.ViewState["ImageString"]);
}
return new List<int>();
}
set { this.ViewState["ImageString"] = value; }
}
And then I was hoping that from my aspx page I could add a line of code to add a value to the list like so:
this.LightBoxControl.ImageString.Add(value);
The problem I'm getting is that the the value is actually never added to the list. The count is always zero.
I'm sure its just that I've set the property up wrong, but I'm not sure how to right it..
Any help would be greatly appreciated.
Thanks
Al

Your getter is wrong. This is the correct variant:
get {
if (this.ViewState["ImageString"] == null) {
this.ViewState["ImageString"] = new List<int>();
}
return (List<int>)(this.ViewState["ImageString"]);
}
Here you first check whether there is something you need in ViewState already, and if there is no, you add it there. Then you return the item from ViewState - it is guaranteed to be there.
Your solution was bad because it did not place new List<int>() into the ViewState

Using Jquery to prevent a "Submit Button" from posting data if a field is left blank

So I'm putting together a little registration area for my web project, here. The user inputs various strings such as "Username", "Password", etc.
I already have a bit of code set up in order to prevent duplicate Usernames or Passwords in the database. I also have a guard in place if the "Password" and "Repeat Password" fields don't match.
What I'm trying to do now is to -
1: If the user attempts to Submit data while a field is blank, it will not post.
2: Display a "Fields cannot be blank" div I've assigned "display: none" to.
I was thinking something along the lines of assigning the input fields a class of "Required", and using some sort of code such as
if == null
.show;
return false; //To prevent the rest of the function (the submit button posting to login/register) from firing.
Running into obscene problems. Anyway. Here's what I have so far.
$("#SubmitButton").click(function () { //Click Submit
if ($("#PassReg").val() != ($("#PassConfirm").val())) { //Both fields match
$("#PasswordMismatch").show(); //Or this div shows you messed up
return false; //And nothing else fires
}
$.post("login/register", $('#ConfirmPanel *').serialize(), function (result) {
if (result == 2) //Json return from C#
$("#UsernameInUse").show(); //Shows an error div
else if (result == 3) //Json return from C#
$("#EmailInUse").show(); //Shows an error div
else {
$("#ConfirmPanel").dialog('close'); //Closes the registration dialog
}
});
});
Any thoughts? At first I thought that I literally -cannot- use "class" to mark an input field, and then have that input field compared to a null value. I don't know, though.

You should use the .submit() jquery event handler on the form instead of .click() on the button. Then return false to prevent the normal form submission if needed.

Since you are trying to submit the form using $.post you should stop the default behavior of the form submit by alwasy returning false from submit button click handler.
$("#SubmitButton").click(function () { //Click Submit
if ($("#PassReg").val() != ($("#PassConfirm").val())) { //Both fields match
$("#PasswordMismatch").show(); //Or this div shows you messed up
return false; //And nothing else fires
}
$.post("login/register", $('#ConfirmPanel *').serialize(), function (result) {
if (result == 2) //Json return from C#
$("#UsernameInUse").show(); //Shows an error div
else if (result == 3) //Json return from C#
$("#EmailInUse").show(); //Shows an error div
else {
$("#ConfirmPanel").dialog('close'); //Closes the registration dialog
}
});
return false;
});

The jQuery way of preventing form submission is to use preventDefault(), like:
$("#SubmitButton").click(function (event) { //Click Submit
if ($("#PassReg").val() != ($("#PassConfirm").val())) { //Both fields match
$("#PasswordMismatch").show(); //Or this div shows you messed up
event.preventDefault(); //And nothing else fires
return;
}
//...
});
However, since you are posting the form asynchronously when validation passes, what you really want is something more along the lines of:
$("#SubmitButton").click(function (event) { //Click Submit
event.preventDefault(); //we don't ever want to allow the default behavior
if ($("#PassReg").val() != ($("#PassConfirm").val())) { //Both fields match
$("#PasswordMismatch").show(); //Or this div shows you messed up
return;
}
//post the form
});
The rest of what you suggest (using a class to mark each required input field, checking them all for empty strings) is reasonable.
Be aware that because you are binding the button's click event instead of the form's submit event it is entirely possible for the user to submit your form without ever clicking on your button and triggering your validation code. For instance, by pressing return from any one of your text fields.
Also note that in this case you may find it more convenient to just use a traditional onsubmit directive on the form, like:
<form onsubmit="validateAndPost(); return false;">
<!-- inputs and buttons, etc. -->
</form>
<script>
function validateAndPost() {
if ($("#PassReg").val() != ($("#PassConfirm").val())) { //Both fields match
$("#PasswordMismatch").show(); //Or this div shows you messed up
return;
}
//post the form
}
</script>
Example: http://jsfiddle.net/AwxGE/

I admire your desire to use jquery, however I would advise using a normal ASP.NET ReqiredFieldValidator control. As well as making your page substantially more concise and easy to maintain, it also allows you to very simply invoke server-side validation:
public void submitbutton_click(object sender, EventArgs args){
Page.Validate();
if(Page.IsValid){
doStuff();
}
}
Please don't reinvent the wheel, and don't trust the browser to behave as you think it will.

use this -
$(document).on('click', '#SubmitButton', function () {
`enter code here`
});

Asp.Net ViewState lost with RegisterClientScriptBlock

I am validating a zip code using Javascript that is generated server-side, and injected when a LinkButton is clicked. Then, I retrieve the return value by calling a server-side function when the page loads.
This works nicely, but the problem is that the ViewState is completely lost after PostBack. Below is the code, starting with the page_load event, the button click event, and then the callback called from the page_load event.
Is there a way I can somehow save the ViewState, maybe easily in a session variable? Or is there a workaround I can use?
// In Page_Load
if (Request.Form["__EVENTTARGET"] == "CallFunction") {
GetValidateZipCodeScriptReturnValue(Boolean.Parse(Request.Form["__EVENTARGUMENT"].ToString()));
}
// OnClick for LinkButton
private bool ValidateZipCode(string zip) {
StringBuilder script = new StringBuilder();
script.Append("<script language='javascript' type='text/javascript'>");
script.Append(#"var regex = /^\d{5}$|^\d{5}-\d{4}$/;");
script.Append("__doPostBack('CallFunction', regex.test(" + zip + "));");
script.Append("</script>");
Type t = GetType();
if (!ClientScript.IsClientScriptBlockRegistered(t, "ValidateZipCodeScript")) {
ClientScript.RegisterClientScriptBlock(t, "ValidateZipCodeScript", script.ToString());
}
return false;
}
// Method called on PostBack to get the return value of the javascript
private void GetValidateZipCodeScriptReturnValue(bool valid) {
m_ZipCode = uxZip.Text;
if (valid) {
Response.Redirect(string.Format("~/checkout/overview.aspx?pc={0}&zc={1}",
ProductCode, ZipCode));
}
else {
Alert.Show("The entered zip code is invalid. Please ensure the zip code is a valid zip code.");
SetupPostBackViewState();
ScrollToZipCode();
}
}

Why not just use the OnClick event of the LinkButton? Or, better yet, look into the CustomValidator control, since it looks like all you're trying to do is validate a zip code and that's exactly what a CustomValidator can do (you'll need to look at the ClientValidationFunction, which is where you want to put your regex test).