Maximum custom window loses drop shadow effect

Question

I have a custom WPF window defined as:

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" MinHeight="300" Height="350" MinWidth="600" Width="700"      ResizeMode="CanResizeWithGrip" AllowsTransparency="True" WindowStyle="None">

I found a class online that creates drop shadows, shown below. This works well, even with a resize grip, until I maximise the window. Once I maximise the window or change the window state of another window (eg. Visual Studio), I loose the drop shadow and I cannot get it back. Any Ideas?

Drop Shadow Class:

Public Class DropShadow

Private Shared _handler As EventHandler = New EventHandler(AddressOf window_SourceInitialized)

<DllImport("dwmapi.dll", PreserveSig:=True)> _
Private Shared Function DwmSetWindowAttribute(hwnd As IntPtr, attr As Integer, ByRef attrValue As Integer, attrSize As Integer) As Integer

End Function

<DllImport("dwmapi.dll")> _
Private Shared Function DwmExtendFrameIntoClientArea(hWnd As IntPtr, ByRef pMarInset As Margins) As Integer
End Function

Public Shared Sub DropShadowToWindow(window As Window)
    If Not DropShadow(window) Then
        AddHandler window.SourceInitialized, _handler
        AddHandler window.SizeChanged, New SizeChangedEventHandler(AddressOf windowSizeChanged)
    End If
End Sub

Private Shared Sub window_SourceInitialized(sender As Object, e As EventArgs)
    Dim window As Window = DirectCast(sender, Window)

    DropShadow(window)

    RemoveHandler window.SourceInitialized, _handler
End Sub


Private Shared Function DropShadow(window As Window) As Boolean
    Try
        Dim helper As New WindowInteropHelper(window)
        Dim val As Integer = 2
        Dim ret1 As Integer = DwmSetWindowAttribute(helper.Handle, 2, val, 4)

        If ret1 = 0 Then
            Dim m As New Margins() With { _
             .Bottom = 0, _
             .Left = 0, _
             .Right = 0, _
             .Top = 0 _
            }
            Dim ret2 As Integer = DwmExtendFrameIntoClientArea(helper.Handle, m)
            Return ret2 = 0
        Else
            Return False
        End If
    Catch ex As Exception
        ' Probably dwmapi.dll not found (incompatible OS)
        Return False
    End Try
End Function

Private Shared Sub windowSizeChanged(sender As Object, e As SizeChangedEventArgs)
    Dim window As Window = DirectCast(sender, Window)
    DropShadow(window)
End Sub
End Class

When you debug it, what is the first return value from DropShadow? If it is returning False, the event handler won't be hooked up and the DS will disappear when you resize it. — Chris Shain
It was setting the handlers correctly. I have decided to remove it and try it a different way. I'll post the way I did it in a bit... — Stuart Blackler

Alastair Pitts Alastair Pitts · Accepted Answer · 2011-12-29T07:11:51

So I found out a way to get this to work.

You need to use the WPF Shell Integration Library (here) to do the work for you. As it's been written by MS, they have fixed (it seems) any issues with doing to the P/Invoke code.

So it is easy to get a Window that has no Aero glass, is resizable on the edges, has a caption area that behaves with Aero snap, and has a drop shadow that reappears after min/maxing.

This is the code for my window (note, you need to have referenced Microsoft.Windows.Shell)

<Window x:Class="MyLibrary.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:shell="http://schemas.microsoft.com/winfx/2006/xaml/presentation/shell"
        Title="MainWindow"
        WindowStyle="SingleBorderWindow"
        ResizeMode="CanResizeWithGrip"
        mc:Ignorable="d"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        d:DesignHeight="449"
        d:DesignWidth="677"
        Foreground="White"
        Background="Black">

    <shell:WindowChrome.WindowChrome>
        <shell:WindowChrome CaptionHeight="35"
                            GlassFrameThickness="0,0,0,1"
                            ResizeBorderThickness="5" />
    </shell:WindowChrome.WindowChrome>

    <Grid x:Name="LayoutRoot">

    </gGrid>
</Window>

The <shell:WindowChrome> is where you set all the different variables for the interop.

CaptionHeight: This is the height of the caption area (headerbar) that allows for the Aero snap, double clicking behaviour as a normal title bar does.
GlassFrameThickness: Setting this to 0,0,0,1 for some reason removes the chrome (glass), keeps the square border, and adds a drop shadow.
ResizeBorderThickness: This is thickness at the edge of the window which is where you can resize the window.

Other things to note as that you keep the Window.WindowStyle property equal to SingleBorderWindow and let the Shell Library deal with removing the title, buttons and other chrome.

So I kinda wasted my bounty there, but it looks like a completely viable solution that works a treat!

EDIT:

Here is a picture of the result: Sample Metro WPF Application

I also put up a sample project on http://code.google.com/p/sample-metro-wpf-application/. It's an MIT license and people can use it however they want.

Maximum custom window loses drop shadow effect

3 Answers