Try out this [test project](https://skydrive.live.com/redir?resid=9935281CD314F220!25986) I created for this example

Here's a little bit of explanation:

It's very important to pay attention to scope.  `Object reference not set to an instance of an object` is a very common error, one that usually indicates a need for some kind of architectural adjustment.

Here's the setup for the **MyMenuForm** class.  The DataTable is declared as a property of that class, so anybody who can access the class, can access that particular property.



    Public Class MyMenuForm
    
        Public DataGridTable As New DataTable
    
        Private Sub LoadForm(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
            With DataGridTable.Columns
                .Add("Name", GetType(String))
                .Add("Verison", GetType(String))
                .Add("Compile", GetType(Button))
                .Add("Location", GetType(String))
                .Add("CompileLoc", GetType(String))
            End With
            DataGridView1.DataSource = DataGridTable
        End Sub
    
    End Class

You'll also need to make sure that the `MyMenuForm` has been created before you try to add rows with the `AddForm` class.  In my case, I just added it as the startup form and opened up an add form on click

![Startup From][1]

In the **AddForm**, make sure you reference the `DataGridTable` property on the `MyMenuForm` class, like so:



    Private Sub AddButton_Click(sender As System.Object, e As System.EventArgs) Handles AddButton.Click
        Dim row As DataRow = MyMenuForm.DataGridTable.NewRow()

        With row
            .Item("Name") = "TestName"
            .Item("Verison") = "TestVerison"
            .Item("Compile") = New Button
            .Item("Location") = "TestLocation"
            .Item("CompileLoc") = "TestCompileLoc"
        End With

        MyMenuForm.DataGridTable.Rows.Add(row)

    End Sub
  [1]: http://i.stack.imgur.com/MRoIY.png

So i have this code in the form called `MyMenuForm`. 

    Public Class MyMenuForm

        Public Sub LoadForm(sender As Object, e As EventArgs)
            DataGrid.DataSource = DataGridTable
            DataGridTable.Columns.Add("Name", GetType(String))
            DataGridTable.Columns.Add("Verison", GetType(String))
            DataGridTable.Columns.Add("Compile", GetType(Button))
            DataGridTable.Columns.Add("Location", GetType(String))
            DataGridTable.Columns.Add("CompileLoc", GetType(String))
        End Sub

        Public DataGridTable As DataTable

    End Class

I want to be able to edit `DataGridTable` from a different form called `AddForm`.

    Public Class AddForm

        Public Sub Add_Click(sender As Object, e As EventArgs) Handles AddButton.Click
            MyMenuForm.DataGridTable.Rows.Add(NameBox(), VersionBox(), "Compile", LocationBox(), CompileBox())
        End Sub

    End Class

When I click on the `AddButton` button, I receive the error

    Additional information: Object reference not set to an instance of an object.

Does anyone know why this happens or how I can fix it? I have googled to the extent of my ability and have found no solution. Please Help.

Change the datatable in Form1 from Form2 Visual Basic

If your `<asp:ContentPlaceHolder ID="MainContent" >` control is, itself, inside of a `form` element, then you shouldn't place a `form` inside of the `asp:content` control as you should not have nested forms.

From the [HTML5][HTML5] working draft:
> 4.10.3 The form element  
> Content model:  
> Flow content, but with no form element descendants.

**UPDATE**

See the question [A page can have only one server-side Form tag][SO]:

> Master pages should not contain form tags in general because they are meant to be used only as the base layout of your content page. 

Try to restructure your project using these guidelines:

* Only add `form` elements to aspx pages
* Add main content to `MasterPage` from pages
* Add any content that needs to be nested within a form to a `UserControl` that is placed within a page.


[SO]: https://stackoverflow.com/a/15480367/1366033
[HTML5]: http://www.w3.org/TR/2011/WD-html5-20110525/forms.html#the-form-element

I have a content page in an asp.net application that uses a form tag. There's only one on the page so I'm confused why its give me the error: Validation (HTML5): Element 'form' must not be nested within element 'form'

Heres the code:

    <%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/Site.Master" CodeBehind="Default.aspx.cs" Inherits="WebApplication6._Default" %>
    <asp:Content ID="Content1" runat="server" ContentPlaceHolderID="MainContent">
       <div>
          <form id="form1">
             <asp:GridView ID="GridView1" runat="server" AllowSorting="True" AutoGenerateColumns="False" DataKeyNames="Id" DataSourceID="SqlDataSource1" AllowPaging="True" OnSelectedIndexChanged="GridView1_SelectedIndexChanged">
                <Columns>
                   <asp:BoundField DataField="Id" HeaderText="Id" InsertVisible="False" ReadOnly="True" SortExpression="Id" />
                   <asp:BoundField DataField="Title" HeaderText="Title" SortExpression="Title" />
                   <asp:BoundField DataField="Director" HeaderText="Director" SortExpression="Director" />
                   <asp:BoundField DataField="DateReleased" HeaderText="DateReleased" SortExpression="DateReleased" />
                   <asp:TemplateField HeaderText="Selection">
                      <ItemTemplate>
                         <asp:CheckBox ID="Selections" runat="server" OnCheckedChanged="CheckBox1_CheckedChanged1" />
                      </ItemTemplate>
                   </asp:TemplateField>
                </Columns>
             </asp:GridView>
             <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" SelectCommand="SELECT * FROM [Movies]"></asp:SqlDataSource>
             <asp:Button ID="Button1" runat="server" Text="Select Movies" OnClick="Button1_Click" CausesValidation="False" />
             <asp:TextBox ID="TextBox1"  Text="First Name" runat="server"></asp:TextBox>
          </form>
       </div>
    </asp:Content>

I have a form in my masterpage but that wasnt giving me problems yesterday..

Any ideas?




asp.net error form cannot be nested within element form?

From Bootstrap Documentation on [Inline Forms][Forms]

>**Requires custom widths**: Inputs, selects, and textareas are 100% wide by default in Bootstrap. To use the inline form, you'll have to set a width on the form controls used within.

---

Just apply the following css if you want all the inputs to be the same size



    .form-group {
        width: 300px;
    }
    .form-group input {
        width: 300px;
    }

[bootply with css][bootply]
===

-----


**OR** fix the width of each of your form groups by adding `col-md-4` class to each group like this:



    <div class="form-group col-md-4">
        <label for="id_telephone">Phone</label>
        <input type="text" name="phone" class="form-control" id="id_telephone">
    </div>

[bootply with classes][bootply2]
====

[Forms]: http://getbootstrap.com/css/#forms-inline
[bootply]: http://bootply.com/92494
[bootply2]: http://bootply.com/92495

I want a form to have three controls in each row. But the width of the control in every row is different(less to be exact). Must I always use columns? Is that regular behaviour of css? Sometimes the css feels like a labyrinth to me 

**Here's what I have so far:**

[bootply][bootply]
====



    <form action="" method="post" role="form" class="form-inline">
        <div class="container">
            <div class="row">
                <div class="form-group">
                    <label for="id_firstname">First Name</label>
                    <input type="text" name="firstname" class="form-control" id="id_firstname">
                </div>
                <div class="form-group">
                    <label for="id_middlename">Middle Name</label>
                    <input type="text" name="middlename" class="form-control" id="id_middlename">
                </div>
                <div class="form-group">
                    <label for="id_lastname">Last Name</label>
                    <input type="text" name="lastname" class="form-control" id="id_lastname">
                </div>
            </div>
        </div>
        <div class="container">
            <div class="row">
                <div class="form-group">
                    <label for="id_address">Address</label>
                    <input type="text" name="address" class="form-control" id="id_address">
                </div>
                <div class="form-group">
                    <label for="id_postalcode">Postal Code</label>
                    <input type="text" name="postalcode" class="form-control" id="id_postalcode">
                </div>
                <div class="form-group">
                    <label for="id_city">City</label>
                    <input type="text" name="city" class="form-control" id="id_city">
                </div>
            </div>
        </div>
        <div class="container">
            <div class="row">
                <div class="form-group">
                    <label for="id_telephone">PHone</label>
                    <input type="text" name="phone" class="form-control" id="id_telephone">
                </div>
                <div class="form-group">
                    <label for="id_mobile">Mobile</label>
                    <input type="text" name="mobile" class="form-control" id="id_mobile">
                </div>
                <div class="form-group">
                    <label for="id_email">E-mail</label>
                    <input type="text" name="email" class="form-control" id="id_email">
                </div>
            </div>
        </div>
    </form>

Sorry thought you only wanted the link. I  also wrapped every .form-group with .col-md-4 but still the width of the inputs differ from each other

[bootply]: http://bootply.com/92488

Bootstrap rows and form-inlines changing width of inputs

BTW, the current answer is deprecated according to the docs on [Skipping validation on submit][1]:

>To skip validation while still using a submit-button, add the attribute `"formnovalidate"` to that input:
>
>
>    
    <input type="submit" name="go" value="Submit">
    <input type="submit" formnovalidate name="cancel" value="Cancel">

>*This used to work by adding `class="cancel"` to the input, this is now deprecated.*

Although, as of version 1.17, both methods still appear in the [source code][2]:

> **`...blob/1.17.0/src/core.js#L34`**:

>
>
    // Allow suppressing validation by adding a cancel class to the submit button
	if ( $( this ).hasClass( "cancel" ) ) {
		validator.cancelSubmit = true;
	}
>
	// Allow suppressing validation by adding the html5 formnovalidate attribute to the submit button
	if ( $( this ).attr( "formnovalidate" ) !== undefined ) {
		validator.cancelSubmit = true;
	}


Further Reading: [jQuery Validation plugin: disable validation for specified submit buttons][3]

[1]:https://jqueryvalidation.org/reference/#link-skipping-validation-on-submit
[2]: https://github.com/jquery-validation/jquery-validation/blob/1.17.0/src/core.js#L34
[3]:https://stackoverflow.com/q/203844/1366033

I have a form that I want to be able to save without validating, but validates on submit. I've got two buttons on this form to either save or submit.

The problem is: if I use a "submit" button to save (and then do a switch on which action in the controller), jquery.validate kicks in and I can't save a partially-filled out form.

If I do it as a link, I don't know how to make the form post to the new action in the controller.

Here's the HTML from the view:
    
    <a class="btn  btn-default" data-placement="right" data-title="Save your progress." href="/Summary/Save/2" rel="tooltip"><i class="glyphicon glyphicon-floppy-disk"></i> Save Summary</a> 
    <a class="btn  btn-default" confirm="Are you sure you want to revert to the previous saved copy? You will lose all changes since your last save." data-placement="right" data-title="Revert back to your last saved copy." href="/Summary/Revert/2" rel="tooltip"><i class="glyphicon glyphicon-remove"></i> Revert Changes</a> 
    <button class="btn-default  btn btn-primary" confirm="This will submit the summary to the evaluator for review. No changes will be allowed unless the evaluator returns it. Are you sure?" type="submit">Submit Summary</button>

MVC bypass client-side validation ("save progress" vs "submit")

There are several libraries & native APIS to handle client side validation that are worth leveraging

### [HTML 5 Form Validation][1]

You can use the `required` attribute in any input and the browser will block client side submits:



<pre><code>&lt;input id="name" name="name" <b><i>required</i></b> &gt;</code></pre>

For more advanced handling, you can also wire up Javascript using the [Constraint Validation API][2]

### jQuery Validate

Another popular client side validation framework is the [jQuery Validation Plugin][3]


### Custom JavaScript

If you want to write yourself... assuming all fields are required, you'll need to capture change events to all inputs, verify that all inputs have a value, and then conditionally toggle the disabled attribute on the submit button.  In jQuery, it would look something like this:



    // get all input elements and attach listener
    var $inputs = $("#myForm :input:not([type='submit'])")
    $inputs.change(function() {
    
      // check if all elements have value
      var allInputsHaveValue = $inputs.toArray().every(function(el) {
        return !!el.value
      });
    
      // toggle submit disabled
      $("#submit").prop("disabled", !allInputsHaveValue);
    
    }).change(); // run on init

[**Demo in jsFiddle**][4]


[1]: https://developer.mozilla.org/en-US/docs/Learn/HTML/Forms/Form_validation

[2]: https://developer.mozilla.org/en-US/docs/Learn/HTML/Forms/Form_validation#The_HTML5_constraint_validation_API

[3]: http://jqueryvalidation.org/documentation/
[4]: https://jsfiddle.net/KyleMit/R8c8h/

How can I check if form is not empty and if form is empty then set `disabled="disabled"` into submit button?

    <form action="/contact/" method="POST" id="form">
        <input type="text" id="name" name="name" class="form-control" placeholder="Name">
        <input type="email" id="email" name="email" class="form-control" placeholder="E-Mail">
        <textarea name="msg" id="msg" class="form-control" rows="4" placeholder="Message"></textarea>
        <input type="submit" value="Send" class="button-contac-send">
    </form>

        

How can I check if form is not empty and if form is empty then set disabled="disabled" into submit button?

You can use this [polyfill library][polyfill library] with the setting `{hideOnFocus : false}` - 
[Here's a demo][polyfill demo]

-----

A homerolled approach is going to be a little longer, but here goes:

# [Here's a Working Demo in Fiddle][fiddle]

First, figure out if you [need to use a polyfill in the first place][placeholder feature detection]:

    function placeholderIsSupported() {
        var test = document.createElement('input');
        return ('placeholder' in test);
    }

Then select everything that has the placeholder attribute  `[placeholder]` and loop through each:

    function placeholderPolyfill() {
        // added for purposes of debugging on modern browsers
        var alwaysUsePolyfill = true;
    
        if (alwaysUsePolyfill || !placeholderIsSupported()) {
            $("input[placeholder]").each(function() {
                // place code here
            });
        }
    }

For each element, we want to assign the `value` of the control with the value in the `placeholder` and add a class so we can make it look different than regular input text:

    $(this).val(this.placeholder)
           .addClass('placeholder')

Here I'm using a shade of blue to help differentiate it for the purposes of debugging, but you might want to pick a shade of grey.

    input.placeholder {
        color: #1A89AD;
    }


We'll also need a way to [place the caret/cursor at the beginning of the text][Set Cursor Position]:

    $.fn.selectRange = function(start, end) {
        if(!end) end = start; 
        return this.each(function() {
            if (this.setSelectionRange) {
                this.focus();
                this.setSelectionRange(start, end);
            } else if (this.createTextRange) {
                var range = this.createTextRange();
                range.collapse(true);
                range.moveEnd('character', end);
                range.moveStart('character', start);
                range.select();
            }
        });
    };

Normally, polyfills work by clearing the `value` when the `onfocus` event fires. But not us, right guy. In order to work around this, we'll listen to three different events.  We want to know when the control is focused (`mouseup keyup`), when typing has started (`keydown`), and when typing has finished (`keyup`).

Here's each one:

When the element gets focus, we want to move the cursor to the beginning.  Because of [complications with the way chrome sets the cursor during the focus event][chrome focus cursor position], we have to listen to `mouseup` and `keyup` instead.

    .on('mouseup keyup': function(e) {
         // if we moused or tabbed in
         if (e.type == "mouseup" ||  e.keyCode == 9) {
             // pretend like their are no chars
             $(this).selectRange(0);
         }
    });

When someone starts typing, if the current value is equal to the placeholder value, then we'll clear out the text to make room for more typing.  On the keyup we can replace the text if need be.  Since tabbing through the fields will [fire a keyup on the next field, not the current one][tab keyup], if the keydown that was pressed was the tab key, we'll also trigger the keyup event manually.

    .on('keydown': function(e)
         // check if we still have the placeholder
         if (this.value == this.placeholder) {
             $(this).val('').removeClass('placeholder'); 
         } 
         // if tab key pressed - run keyup now
         if (e.keyCode == 9) {
             $(this).trigger('keyup');
         }
    });

Finally when the keystrokes are done being registered, let's re-check the input.  If we don't have any values, we've either cleared the area or deleted the last character.  Either way, let's repopulate the value, add back the placeholder class, and set the caret to the beginning again:

    .on('keyup': function(e)
          // if we're back to zero 
          if (this.value.length === 0) {
              // add placeholder back
               $(this).val(this.placeholder)
                      .addClass('placeholder')
                      .selectRange(0);
          }
    });

That's pretty much it.  See the fiddle for the full code sample.

[polyfill library]: https://github.com/ginader/HTML5-placeholder-polyfill
[polyfill demo]: http://blog.ginader.de/dev/jquery/HTML5-placeholder-polyfill/docs/index-chromeish.html

[placeholder feature detection]: https://stackoverflow.com/a/8263907/1366033
[Set Cursor Position]: https://stackoverflow.com/a/841121/1366033
[chrome focus cursor position]: https://stackoverflow.com/q/3150275/1366033
[tab keyup]: https://stackoverflow.com/a/18020246/1366033

[fiddle]: http://jsfiddle.net/KyleMit/An9t6/

I am using this fix http://www.hagenburger.net/BLOG/HTML5-Input-Placeholder-Fix-With-jQuery.html for placeholder feature for IE which works fine but I would like the placeholder text to remain till at least a single character is typed. I have tried the following which isn't working for me (the bit in the asterisk (**) is my addition:

    if (input.val() == input.attr('placeholder') **&& input.val().length>0** ) {
		input.val('');
		input.removeClass('placeholder');    
    }

Thanks