How do you disable Aero Snap in an application?

Question

Is it possible to disable the automatic window-docking feature of Windows 7 in a WPF application?

Answer 1

Here's my solution. Windows will not snap if their ResizeMode is set to ResizeMode.NoResize, therefore, the trick is to determine reliably when a drag/move begins and ends.

EDIT: alexandrud correctly pointed out that this will only work for "borderless" windows (WindowStyle = None in WPF terms).

Many Bothans died to bring us this information.

class NoSnapWindow : System.Windows.Window
{
    public NoSnapWindow()
    {
        SourceInitialized += delegate {
            var source = HwndSource.FromVisual(this) as HwndSource;
            source.AddHook(SourceHook);
        };
    }

    private IntPtr SourceHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        switch (msg)
        {
            case 0x112: // WM_SYSCOMMAND
                switch (wParam.ToIn32() & ~0x0F)
                {
                    case 0xF010: // SC_MOVE
                        ResizeMode = ResizeMode.NoResize;
                        break;
                }
                break;
            case 0x2A2: // WM_MOUSELEAVE
                ResizeMode = ResizeMode.CanResize;
                break;
        }

        return IntPtr.Zero;
    }
}

Answer 2

If you are giving example of "Sticky Notes" of Win7, you may have noticed that it does NOT have standard window border. On that as a base, I can only tell you that there's no direct way of doing this except you set ResizeMode="NoResize" and handling the resize behavior manually. Following is a very basic, non-professional solution that i've quickly created to get you started, but you can append more functions if you like :)

<Window
    x:Class="WpfApplication1.Window1"
    x:Name="window"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1"
    Width="300"
    Height="300"
    ResizeMode="NoResize"
    WindowStyle="None"
    AllowsTransparency="True"
    Background="Transparent"
    WindowState="Maximized">

    <Window.Resources>
        <x:Array
            x:Key="TextBlockList"
            Type="{x:Type TextBlock}">
            <TextBlock
                Text="○ Resize Horizontally by dragging right grip" />
            <TextBlock
                Text="○ Resize Vertically by dragging bottom grip" />
            <TextBlock
                Text="○ Move Horizontally by dragging left grip" />
            <TextBlock
                Text="○ Move Verticallyby dragging top grip" />
        </x:Array>
    </Window.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition
                Height="Auto" />
            <RowDefinition
                Height="{Binding Height, Mode=OneWay, ElementName=window}" />
            <RowDefinition
                Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition
                Width="Auto" />
            <ColumnDefinition
                Width="{Binding Width, Mode=OneWay, ElementName=window}" />
            <ColumnDefinition
                Width="Auto" />
        </Grid.ColumnDefinitions>

        <GridSplitter
            Grid.Column="1"
            Grid.Row="1"
            HorizontalAlignment="Left"
            MinWidth="5" />

        <GridSplitter
            Grid.Column="1"
            Grid.Row="1"
            HorizontalAlignment="Right"
            MinWidth="5" />

        <GridSplitter
            Grid.Column="1"
            Grid.Row="1"
            VerticalAlignment="Top"
            MinHeight="5"
            ResizeDirection="Rows"
            HorizontalAlignment="Stretch" />

        <GridSplitter
            Grid.Column="1"
            Grid.Row="1"
            VerticalAlignment="Bottom"
            MinHeight="5"
            ResizeDirection="Rows"
            HorizontalAlignment="Stretch" />

        <Border
            Grid.Column="1"
            Grid.Row="1"
            Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
            Margin="5">

            <Grid x:Name="root">
                <ItemsControl
                    ItemsSource="{StaticResource TextBlockList}" />
            </Grid>

        </Border>

    </Grid>
</Window>

You can even make a control (basically a panel) that can be resized and moved within its parent canvas. Now this control can be filled into a transparent maximized window. This'll give you an illusion of your control being a window that doesn't respond to 'Window Snap' and will not dock!

Hope this helps.
Regards,
Mihir Gokani

Answer 3

A rather simple solution I found that works with borderless windows as well: Just hide the maximize button (event if it's already not displayed due to the lack of caption bar):

    [DllImport("user32.dll")]
    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);
    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
    private const int GWL_STYLE = -16;
    private const int WS_MAXIMIZEBOX = 0x10000;

    private void Window_OnSourceInitialized(object sender, EventArgs e)
    {
            var hwnd = new WindowInteropHelper((Window)sender).Handle;
            var value = GetWindowLong(hwnd, GWL_STYLE);
            SetWindowLong(hwnd, GWL_STYLE, (int)(value & ~WS_MAXIMIZEBOX));
    }

Answer 4

I recently needed to do this to a custom, resizable ResizeMode = CanResizeWithGrip WPF window with no window decorations (no title bar and buttons). I used DragMove() to move the window, and when It is maximized by AeroSnap, the window becomes unmovable and hence locked in place.

I tried Barn Monkey's solution, which partially worked, but it would still show the AeroSnap graphic and resize the app to fullscreen size. I modified it below and now it works as expect: still resizable, but no AeroSnap at all.

void Window1_MouseDown(object sender, MouseButtonEventArgs e)
{
    if( e.LeftButton == MouseButtonState.Pressed )
    {
        // this prevents win7 aerosnap
        if( this.ResizeMode != System.Windows.ResizeMode.NoResize )
        {
            this.ResizeMode = System.Windows.ResizeMode.NoResize;
            this.UpdateLayout();
        }

        DragMove();
    }
}

void Window1_MouseUp( object sender, MouseButtonEventArgs e )
{
    if( this.ResizeMode == System.Windows.ResizeMode.NoResize )
    {
        // restore resize grips
        this.ResizeMode = System.Windows.ResizeMode.CanResizeWithGrip;
        this.UpdateLayout();
    }
}

EDIT:

It's been a while since I wrote this, but since people still look at this I'll update it with what I use now. I still use basically the same method for preventing edge snapping and moving my windows, but I now have them packed into custom Behavior<> classes that I can attach to a Window or UserControl. This makes them very easy to use with MVVM (I use Caliburn Micro).

The behavior classes are:

/// <summary>
/// behavior that makes a window/dialog draggable by clicking anywhere 
/// on it that is not a control (ie, button)
/// </summary>
public class DragMoveBehavior<T> : Behavior<T> where T : FrameworkElement
{
    protected override void OnAttached()
    {
        AssociatedObject.MouseLeftButtonDown += MouseDown;
        base.OnAttached();
    }

    protected override void OnDetaching()
    {
        AssociatedObject.MouseLeftButtonDown -= MouseDown;
        base.OnDetaching();
    }

    void MouseDown( object sender, EventArgs ea ) => Window.GetWindow( sender as T )?.DragMove();
}

public class WinDragMoveBehavior : DragMoveBehavior<Window> { }

public class UCDragMoveBehavior : DragMoveBehavior<UserControl> { }

/// <summary>
/// behavior that makes a window/dialog not resizable while clicked.  this prevents
/// the window from being snapped to the edge of the screen (AeroSnap).  if DragMoveBehavior
/// is also used, this must be attached first.
/// </summary>
/// <typeparam name="T"></typeparam>
public class NoSnapBehavior<T> : Behavior<T> where T : FrameworkElement
{
    ResizeMode lastMode = ResizeMode.NoResize;
    protected override void OnAttached()
    {
        AssociatedObject.MouseLeftButtonDown += MouseDown;
        AssociatedObject.MouseLeftButtonUp += MouseUp;
        base.OnAttached();
    }

    protected override void OnDetaching()
    {
        AssociatedObject.MouseLeftButtonDown -= MouseDown;
        AssociatedObject.MouseLeftButtonUp -= MouseUp;
        base.OnDetaching();
    }

    /// <summary>
    /// make it so the window can be moved by dragging
    /// </summary>
    void MouseDown( object sender, EventArgs ea )
    {
        var win = Window.GetWindow( sender as T );
        if( win != null && win.ResizeMode != ResizeMode.NoResize )
        {
            lastMode = win.ResizeMode;
            win.ResizeMode = ResizeMode.NoResize;
            win.UpdateLayout();
        }
    }

    void MouseUp( object sender, EventArgs ea )
    {
        var win = Window.GetWindow( sender as T );
        if( win != null && win.ResizeMode != lastMode )
        {
            win.ResizeMode = lastMode;
            win.UpdateLayout();
        }
    }
}

public class WinNoSnapBehavior : NoSnapBehavior<Window> { }

public class UCNoSnapBehavior : NoSnapBehavior<UserControl> { }

I then attach them to my dialog box Views with:

<UserControl ...
  xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
  xmlns:util:="...">
  <i:Interaction.Behaviors>
    <util:UCNoSnapBehavior/>
    <util:UCDragMoveBehavior/>
  </i:Interaction.Behaviors>

  ...

</UserControl>

And it just works!

Answer 5

It might not be the perfect solution for you, but for me setting the form as non-resizable did the trick.

Answer 6

I don't have a Windows 7 box here, so I can't test this, but here's what I would try:

1- Create a test form and override the WndProc
2- Test and log specific messages pertaining to Size, Position and WindowState changing.
3- Determine if the messages sent to the window when docked are a combination of Size/Position/WindowState or if there is another, new Windows 7 message (5 minutes of searching didn't reveal anything to me.)
4- Once you have the messages, check to see if there is a "unique" case that is occurring.
5- Modify your code to accommodate that unique case.

If no one else comes up with anything, I might give this a whirl at home this weekend.