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Issue with Postback and Custom Validators in asp.net

I need some help on an issue, related with asp.net validators and postback.
The issue is that I have a page say 'p1' and it has a master page 'm1'. In addition to these I also have a usercontrol 'u1'.
Now, the issue is that on master page 'm1', I have a button that initiates a postback. And on my usercontrol 'u1', I have some fields which I need to check/validate and stop the postback if the fields are invalid.
I have tried using customvalidators and forcefully calling Page.Validate() method. But by doing this, I can see the page.IsValid property is false but sill the postback happens. I have even tried to write a return statement if the control fields are invalid but it doesn't helps..
Please note that I do not want to make any changes in the masterpage as this may have high impact on the other pages.

If clicking a button causes postbacks even when the page is invalid (as in your case it is proven with Page.IsValid property is False), then this means the button isn't configured to check for validations on the client side.
Solution 1:
You need to intialize the "CausesValidation" Property of the Button with the value True"
However, this requires changing the markup of the "Button" on the markup. And this isn't something you wish to perform.
Solution 2:
You can from within your page, access the Button of the Master page from within the Load Event and Initialize the CausesValidation property of the button to True.
Have a look at the following link to find the button from within the master page:
https://msdn.microsoft.com/en-us/library/xxwa0ff0.aspx

Asp Webform Validation One Button multiple groups accordion tabs

I have a webform application that uses asp.net validators. I have a bootstrap accordian (or any accordian jquery etc) and I only want to validate controls that are on the visible panel. I setup a validation group for each panel. I have a single submit button.
I was using jquery to set the validationgroup property, but it seems when done this way, the button ignores the value.
I have tried validating manually but the page seems to skip validation altogether in that case. I am really banging my head against the wall.
<asp:button ID="btnDeleteConfirmation" runat="server" Text="Save" OnClientClick="return Validate();" CausesValidation="False"/>
function Validate() {
var isValid = false;
isValid = Page_ClientValidate(mode);
return isValid;
}
the mode is set when the tab/panel is switched, the value is correct when I check it. The function is called and the return value looks good, but the page postbacks and then i get the following expected error:
Page.IsValid cannot be called before validation has taken place. It should be queried in the event handler for a control that has CausesValidation=True and initiated the postback, or after a call to Page.Validate.
How do others handle validation client side when only one tab/panel needs to be validated and there is a single submit button?

Normally in this case I set the validation groups on each section properly, then on whatever button I need to do the validation I do
Page.Validate(groupName);
Then you can call Page.IsValid and it will only use the validated group. That way you don't have to do anything else. Don't associated a validation group for your button either.

How can I make a RequiredFieldValidator trigger a message elsewhere on the page?

I have a page with a repeater containing RadioButtonLists which have requiredFieldValidators attached to them. I need to keep the RFV next to the control (it's the only way I can get it to work to be honest!)
However, the form is made up of a few sections contained in an accordion. This means that when the form is submitted, the item that has failed validation may not be visible, so the user won't know where the error is.
Is there a way I can also have a message by the submit button which is triggered by an RFV changing saying "please go back and check your answers" or something? I guess I'd need to use JQuery / JavaScript as it would be clientside.

There is a special ValidationSummary control for that:
<asp:ValidationSummary ID="Summary" runat="server"
DisplayMode="SingleParagraph"
HeaderText="Please go back and check your answers" />
This control is used to summarize all validation errors on the page.

Try "ValidationSummary". look for example from here.
http://www.w3schools.com/aspnet/control_validationsummary.asp

stop setting onclick event for asp:LinkButton if no OnClick event was explicitly defined

How do I setup a default setting so that if I do not set an OnClick (i.e the asp.net OnClick attribute) explicitly for an asp:LinkButton tag, it will not render an onclick(html attribute for javascript) attribute client side? By default, asp.net adds an onclick='doPostBack....' for the LinkButton.
Case for use:
There is a LinkButton tag on the page. For this page, if the user has one friend, I only want to run client side code if the button is clicked and would not for any reason want to make a post back. If the user has more than one friend I would want a click to trigger a postback.
Solutions that include the following are not helpful:
Using any asp.net Ajaxtoolkit
Dynamically switching the control type (i.e. if friends == 1 use a asp:Hyperlink)
-I want to avoid this because it is not scalable. There might be many cases where I want an asp:Link tag to do a postback or to not do a postback depending on the user context or user attributes
Using OnClientClick (I am using jQuery would like to avoid this)
Solution that would be helpful if possible:
If I could see server side at runtime whether an OnClick event was explicitly set on an asp:LinkButton tag, this would solve my problem, too. any ideas?

How about rather than dynamically switching the controls (as you mentioned is a solution you don't want), you could always use an asp:HyperLink and set the NavigateUrl property to redirect your page back to itself with a query string of some sort indicating what was clicked.
If you don't want the post to happen at all, simply leave the NavigateUrl property blank.
Of course, this will be pretty worthless if the rest of the page is dependent on ViewState and such.

http://forums.asp.net/t/1129106.aspx
This link explains how to see server side at runtime whether an OnClick event was explicitly set using reflection

How can I validate that several textboxes contain data when I click submit?

I have 10 defined textboxes with strings.
I have to check all if they are not empty while clicking ok button
whats the cleanest way to check them all and when function is at end. each checkbox which was empty to give this a specific CSSclass. perhaps. ClassError. ( which highlights red)
I'm happy for answers.

I would add RequiredFieldValidators to them, as well as a ValidationSummary control.
edit: You can also add fancy AJAX effects with the ValidatorCallout from the AJAX toolkit.
edit: Validator controls also support client-side validation.

Using javascript or C#?
Javascript I will create an array of textbox and loop through it.
C# just go FindControl within a Panel or the Container of the text box and go something like this
foreach(Control C in ContainerID.Controls)
{
if ( C is TextBox )
{
if ( String.IsNullOrEmpty((C as TextBox).Text))
{
// Do things this way
}
}
}

Something like this would work on the client side using jquery:
$('input').filter(function(){return this.value=="";}).css("CSSclass");
edit: I just saw the C# tag, I'll leave this here for posterity though.

What you're doing might be simple enough to do easily with some custom javascript code, though I would say that in general the built in validator controls are both easier to use and more robust than a simple validation routine that someone might write. In addition to client-side validation, the validator controls also perform server-side validation to ensure that the data submitted is truly valid, in case someone has javascript disabled in their browser.
If validator controls are included on the page, then they will include some javascript functions that you can invoke, such as Page_ClientValidate(). I believe this will return a boolean telling you whether validation passed and will trigger the visual indicators that identify what the errors are. You can execute Page_ClientValidate('') to trigger only a group of validator controls; actually I think you must do that in order to trigger validation on any validator controls that have a value in their ValidationGroup property, as I don't think Page_ClientValidate() will trigger their validation logic.
There is a CustomValidator control that you can point to your own client-side function if you want, in case you do have some special validation logic that you can only implement through a custom javascript function. This is nice to use, because then your custom javascript function will be executed by the built-in validator framework along with any other built-in validator controls that you might choose to include on the page.
Side note regarding client-side validation: I suggest that you avoid doing the following to trigger validation:
onclick="return myValidationFunction();"
because if there is any other javascript code being injected into the onclick event, your return statement will prevent it from executing. So instead, I suggest doing this:
onclick="if(!myValidationFunction()) return false;"
That's bitten me enough times that I thought I'd just throw that out there. This problem is particularly noticeable if you have an ASP.Net button on which you've set the UseSubmitBehavior property to false, as it will cause the button to render as an HTML "button" control instead of a "submit" control, and as a result, executing a return statement, either true or false, will prevent the button from triggering a postback.