Just to add to these suggestions, you probably want to optimize for production deployment.  

If you need to check the design mode in the ViewModel, you should only do so when in `DEBUG` mode, otherwise the released version will always have to perform unnecessary checks.  
When developing, if in design mode you can exit the method (or even stub out some fake data).

Put this code as the first line of your constructor (or whatever code is being called):

**C#**:



    #if DEBUG
        if (DesignerProperties.GetIsInDesignMode(new DependencyObject())) return;
    #endif

**VB**:



    #If DEBUG Then
        If DesignerProperties.GetIsInDesignMode(New DependencyObject()) Then Return
    #End If

I'm developing a networked WPF application with the MVVM pattern and it seems that it's running and connecting to servers in the designer.

I know about the IsInDesignMode property, but I'm not sure how to access it in a ViewModel.

How do I stop my ViewModel code from running in the designer?

Here's an extension method to output to any DataTable to a csv (which excel can open)



	Imports System.Text
	Imports System.IO
	Imports System.Runtime.CompilerServices

	Module ExtensionMethods

		<Extension()> _
		Public Sub OutputAsCSV(ByVal dt As DataTable, ByVal filePath As String)
			Dim sb As New StringBuilder()
					
					'write column names to string builder
			Dim columnNames As String() = (From col As DataColumn In dt.Columns Select col.ColumnName).ToArray
			sb.AppendLine(String.Join(",", columnNames))
					
					'write cell value in each row to string builder
			For Each row As DataRow In dt.Rows
				Dim fields As String() = (From cell In row.ItemArray Select CStr(cell)).ToArray
				sb.AppendLine(String.Join(",", fields))
			Next
					
					'write string builder to file
			File.WriteAllText(filePath, sb.ToString())
		End Sub

	End Module

I have a datagrid which populates a datatable, I want to export the DataTable to excel on click of a button. I am using MVVM for this application. So is it ok to implement the export feature in my view? 

Secondly, as i am using xaml and desktop application, how do i capture the grid and its details.

Can any one suggest me some pointers? I am new to this.

Thanks,
Sagar

DataTable to excel conversion

You can call PropertyChange of Greetings from setter of  FirstName and LastName



    Public Property FirstName() As String
        Get
            Return _firstName
        End Get
        Set(ByVal value As String)
            _firstName = value
            OnPropertyChanged("FirstName")
            OnPropertyChanged("Greeting")
        End Set
    End Property

OR 
=

You can subscribe to `PropertyChanged` of your ViewModel in itself 



    AddHandler this.PropertyChanged, AddressOf PropertyChanged

and in `PropertyChanged` you can check which property is changed depending on that you can RaisePropertyChanged for Greeting

Let's say I have a property called `Greeting` that is principally composed of two bound properties: `LastName` and `FirstName`.  Can I subscribe to updates on first and last name so I can force a refresh with `OnPropertyChanged()` for my Greeting property.  Here's a simple example:

**View**



    <TextBox Text="{Binding FirstName}" />
    <TextBox Text="{Binding LastName}" />
    <TextBlock Text="{Binding Greeting}" />

**ViewModel**



    Public Property FirstName() As String
        Get
            Return _firstName
        End Get
    	Set(ByVal value As String)
            _firstName = value
            OnPropertyChanged("FirstName")
        End Set
    End Property

    '... Omitting LastName for brevity ...

    Public ReadOnly Property Greeting() As String
        Get
            Return String.Format("Hello {0} {1}", Firstname, LastName)
        End Get
    End Property

The way this is currently set up, nothing will ever update the Greeting binding.  I could put `OnPropertyChanged("Greeting")` in the setter for `FirstName` and `LastName`, but this feels wrong.  In a more complex example, I'd rather each object just take care of refreshing itself when something changes.  

**Q:)** *Can I force an update for a `ReadOnly` Property when one of the Properties it's composed of changes?*