Setting Window.Datacontext - wpf

Question

I am trying to use my viewmodel as my window's datacontext but am getting the error:
ViewModel is not supported in a Windows Presentation Foundation (WPF) project.
Clearly, I am not understanding something about the syntax and databinding my window to my view model, but I am not sure what it is that I don't know.
Any advice on what I should be reading?
<Window x:Class="SunnyBeam.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="SunnyBeam" Height="488.358" Width="1014.552">
<Window.DataContext>
<ViewModel/>
</Window.DataContext>
<Grid>
</Grid>
</Window>

Answer 1

Usually I set DataContext through codebehind like that:
public partial class Flor1 : Window
{
public Flor1()
{
var dc = new MyViewModel();
dc.LoadData();
DataContext = dc;
InitializeComponent();
}
}
In place of MyViewModel may be anything you want to bind to.

Answer 2

define class like
public class ViewModel
{
public string Name { get; set; }
public ViewModel()
{
}
}
Use it in xaml like
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:ui="clr-namespace:WpfApplication2"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<ui:ViewModel/>
</Window.DataContext>
<Grid>
</Grid>
It should work.

Answer 3

I thought I would throw in my experience with this error.
I had my datacontext setup same as below, and kept getting an error that ViewModel didn't exist, which I know it did. I refused to set it in code behind, simply rebuilding my project actually fixed this error.
<Window.DataContext>
<ViewModel/>
</Window.DataContext>