Changing the start up location of a WPF window

Just set WindowStartupLocation, Height, Width, Left, and Top in xaml:

<Window x:Class="WpfApplication1.Window1" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="Window1" 
    Height="500" Width="500"
    WindowStartupLocation="Manual" 
    Left="0" Top="0">
</Window>

For people who like me wanted to set the position of the window to the current mouse position, you can do it like this:

myWindow.WindowStartupLocation = WindowStartupLocation.Manual;
myWindow.Left = PointToScreen(Mouse.GetPosition(null)).X;
myWindow.Top = PointToScreen(Mouse.GetPosition(null)).Y;

I like to use WindowStartupLocation="CenterOwner" (MSDN docs for it)

The caller needs to specify itself as owner for this to work though, such as:

new MyWindow() { Owner = this }.ShowDialog();

Then just define the window height and width, e.g:

<Window ...
     Height="400" Width="600"
     WindowStartupLocation="CenterOwner"
>
...