To get the value of a row in a specific column, you can use parenthesis right after the row object and specify the `ColumnName` or `ColumnIndex` property to get the value.

Also, when there is more than one potential value, you can ue a `case` statement, instead of a lot of `ElseIf` statements.  

### MVCE Setup

```vb
'declare local variables
Dim dr As DataRow

'create table
Dim studentLogs As New DataTable("StudentLogs")

'add columns
With studentLogs
    .Columns.Add("Status", GetType(Integer))
    .Columns.Add("OtherCol1", GetType(String))
End With

'add values
With studentLogs
    dr = studentLogs.NewRow()
    dr("Status") = 1
    dr("OtherCol1") = "Joey"
    studentLogs.Rows.Add(dr)
End With
```

### Check Column Value / Row Status

```vb
For Each row As DataRow In studentLogs.Rows
    Select Case row("Status")
        Case 1
            Call SENDSMS()
        Case 2
            MsgBox("2")
            Exit For
        Case 3
            MsgBox("3")
    End Select
Next
```


I have table named `studentlogs`, and it has column status on it. When I finished inserting records on student logs, I want to use an `if .. else` statement. The status column can only have 3 values: `1`, `2` or `3`. 

Now, I want to do the following after I insert the records:

```vb
if status="1" then
   CALL SENDSMS()
ENDif
if status="2" then
   msgbox("")
ENDif
if status="3" then
   msgbox("")
```

How can I do it when I am dealing with columns?

If Else using Column in Table

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

Normally when I want to grab a copy of an existing `DataTable` I call the [`Copy`](http://msdn.microsoft.com/en-us/library/system.data.datatable.copy.aspx) method are return the value to a new object.

I've been cleaning up some legacy code and noticed using [`Clone`](http://msdn.microsoft.com/en-us/library/system.data.datatable.clone.aspx) and then iterating through each row and calling `ImportRow` into the new `DataTable`. 



    'is this...
    TempTable = myDataTable.Clone
    For Each dr As DataRow In myDataTable.Rows
        TempTable.ImportRow(dr)
    Next
    
    'the same as this...
    TempTable = myDataTable.Copy

I'd like to clean it up and simplify by using the `Copy` method, but just want to make sure I'm not breaking anything.  Is there a difference between the two methods here about holding references or doing a deep vs. shallow copy?

Is there a difference between Clone and Import Vs Copying a DataTable

This doesn't specifically use load or fill, but you can do this pretty easily by just reading in the data reader and only setting values when the incoming value isn't null.  By getting the [`SchemaTable`](http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable(v=vs.100).aspx) from the `SqlDataReader`, you can still retain the simplicity of the load or fill commands by not having to write out every column name.  By adding an Extension method with the name Load that takes in a default row parameter, you can retain the look and feel of the Load function while implementing the functionality yourself

**Load Extension Method with Default Row Arg:**



    ''' <summary>
    ''' Fills a <c>System.Data.DataTable</c> with values from a data source using the supplied <c>System.Data.SqlDataReader</c>.<br/>
    ''' Each row is new row is given the default values from the new row and incoming nulls are ignored
    ''' </summary>
    ''' <param name="dt">DataTable to fill</param>
    ''' <param name="reader">A <c>System.Data.SqlDataReader</c> that provides a result set.</param>
    ''' <param name="defaultRow">Default values for each DataRow</param>
    ''' <remarks></remarks>
    <Extension()> _
    Public Sub Load(ByVal dt As DataTable, ByVal reader As SqlDataReader, ByVal defaultRow As DataRow)
        Dim newRow As DataRow
        'get incoming data fields
        Dim columns As List(Of String)
        columns = reader.GetSchemaTable.AsEnumerable _
                        .Select(Function(r) CStr(r("ColumnName"))).ToList()

        While reader.Read()
            'make new row and set default item array
            newRow = dt.NewRow()
            newRow.ItemArray = defaultRow.ItemArray
            'copy over new values
            For Each col As String In columns
                If Not IsDBNull(reader(col)) Then newRow(col) = reader(col)
            Next
            dt.Rows.Add(newRow)
        End While
    End Sub

**Call into your Load Method Like This:**



    Dim roleTable As New CodeSetSchemas.EntityByRoleDataTable()
    Using reader As SqlDataReader = cmd.ExecuteReader()
        roleTable.Load(reader, roleTable.NewEntityByRoleRow())
    End Using

I have an xsd DataSet Schema which allows me to define a the structure for a `DataTable`.  For every column, I've set a default value so when constructing a new row, I get instantiated values ("" for strings and 0 for Ints) instead of `DbNull`

I'd like to preserve that when using either [`DataTable.Load`](http://msdn.microsoft.com/en-us/library/7x8ccbsb.aspx) or [`SqlDataAdapter.Fill`](http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldataadapter.fill.aspx) as in either of the two following method calls



    Dim table1 As New CodeSetSchemas.EntityByRoleDataTable()
    Using reader As SqlDataReader = cmd.ExecuteReader()
        table1.Load(reader)
    End Using
    
    Dim table2 As New CodeSetSchemas.EntityByRoleDataTable()
    Using adapter As New SqlDataAdapter(cmd)
        adapter.Fill(table2)
    End Using

But when either of these methods create a new row, they actually write DbNull from the database into the row.  If I set the `AllowDBNull` property on each column to `False`, I get the following exception:

    Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.

Is there a way to preserve my default values for each row when filling a DataTable?

Use default column values when loading DataTable to avoid Nulls

Using IsDateLastRecallPrintedNull isn't a workaround, it's the way it's intended to be used. If you use a nullable date, you can set this to nothing rather than DateTime.MinValue in your code. Alternatively you can change the datatype in the dataset to System.Object, and then you can select '(Nothing)'  in the dropdown. Note that you can overtype the NullValue entry in the properties with another value that's appropriate for the data type, although it won't work if you enter DateTime.Minvalue - it'll appear to accept it, but then fail - but you can put in another magic number such as 01/01/1900.

All this is 'by design'.*

Using databinding sidesteps this quagmire to a great extent; if you're reading programmatically from the dataset then IsxxxNull is the way to go.

*I suspect this is too often a Microsoftism for 'we didn't finish it by ship date'

When designing data tables in the .xsd designer in Visual Studio, there is a property that specifies what to do when the table encounters a null value:

![screenshot][screenshot]

The problem is, if the `DataType` is `System.DateTime`, I'm unable to return `empty` or `nothing`.  It always throws an exception.  

As I work around, I can do the following:



    If(row.IsDateLastRecallPrintedNull, DateTime.MinValue, row.DateLastRecallPrinted)


But if the value is `DbNull.Value`, I'd rather just have it return that.

[screenshot]: http://i.imgur.com/1hF0Lf1.png