Open ContextMenu programatically

[JaggerJo]

Context:

I have a control that renders elements using an ICustomRenderOperation. When the user right clicks on one of the elements I want to display a context menu at that location. If a user right clicks above no element nothing is supposed to happen.

Problem:

I can't figure out how to manually open and position a context menu.

What I've tried:

I tried embedding a ContextMenu in a Popup but this leads to strange behaviour. (Popup stays open when a MenuItem is clicked, normal ContextMenu would close)

[timunie]

Use ContextFlyout instead

[JaggerJo]

Aha, good to know.

I've tried it but it's not a great fit for my problem. The issue is that I don't handle the right click myself. I just display the context menu IF the user right clicked over an element. If the user right clicks empty space nothing happens.

This is what I currently have. The only remaining issue with this is that the popup stays open even if the user clicks a menu item, but this should be easy to fix by implementing something along the lines of this.

Example:

    <Panel>
        <mainEditor:MainEditorRenderView
            ContextMenuCommand="{Binding ContextMenuCommand}"/>

        <Popup
            IsOpen="{Binding ContextMenu, Converter={x:Static ObjectConverters.IsNotNull}}"
            IsLightDismissEnabled="True"
            Placement="TopEdgeAlignedLeft"
            VerticalOffset="{Binding ContextMenu.ScreenPosition.Y}"
            HorizontalOffset="{Binding ContextMenu.ScreenPosition.X}">

            <ContentControl
                Content="{Binding ContextMenu}">
                <ContentControl.DataTemplates>
                    <DataTemplate x:DataType="mainEditor:NodeContextMenuViewModel">
                        <mainEditor:NodeContextMenu/>
                    </DataTemplate>
                </ContentControl.DataTemplates>
            </ContentControl>
        </Popup>

    </Panel>

[timunie]

If the user right clicks empty space nothing happens.

that's expected. You need a solid background for hittesting, Transparent is okay but not null. Maybe you can alos override hit-testing to configure that.

[JaggerJo]

If the user right clicks empty space nothing happens.

Sorry seems like I formulated that not too well. That's what I expect to happen / desired behaviour.

MainEditorRenderView does all the hit testing, .. internally and invokes ContextMenuCommand with information about where to place the context menu relative to itself and what kind of context menu to show.

What I now want to do:

Show a context menu that is not triggered by right clicking. I want to control in code where to show it and when. I currently do this by wrapping the ContextMenu in a Popup.

The only issue with that implementation is that the Popup remains open when menu items are clicked in the context menu.

That's why I'm looking at replicating what context menus do.

[JaggerJo]

Seems like closed/closing is never invoked if the context menu is not shown via Open(..)

    protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
    {
        base.OnAttachedToLogicalTree(e);

        _contextMenu.Closed += (sender, args) => Console.WriteLine("Close context menu");
        _contextMenu.Closing += (sender, args) => Console.WriteLine("Closing context menu");
    }

[timunie]

I still would use a MenuFlyout:

protected override void OnLoaded(RoutedEventArgs e)
{
    base.OnLoaded(e);

    var flyout = new MenuFlyout()
    {
        Items =
        {
            new MenuItem() {Header = "Hello"},
            new MenuItem() {Header = "Wolrd"},
        },
        Placement = PlacementMode.Center,

    };
    
    flyout.Closing += FlyoutOnClosing;
    
    flyout.ShowAt(this);
}

private void FlyoutOnClosing(object? sender, CancelEventArgs e)
{
    Trace.WriteLine("Closing Me");
}

[JaggerJo]

Seems like I have to mimic what's done here:

Avalonia/src/Avalonia.Controls/ContextMenu.cs

Lines 306 to 356 in bb6005b

	private void Open(Control control, Control placementTarget, PlacementMode placement)
	{
	if (IsOpen)
	{
	return;
	}
	if (_popup == null)
	{
	_popup = new Popup
	{
	IsLightDismissEnabled = true,
	OverlayDismissEventPassThrough = true,
	};
	_popup.Opened += PopupOpened;
	_popup.Closed += PopupClosed;
	_popup.Closing += PopupClosing;
	_popup.KeyUp += PopupKeyUp;
	}
	if (_popup.Parent != control)
	{
	((ISetLogicalParent)_popup).SetParent(null);
	((ISetLogicalParent)_popup).SetParent(control);
	}
	_popup.Placement = placement;
	//Position of the line below is really important.
	//All styles are being applied only when control has logical parent.
	//Line below will add ContextMenu as child to the Popup and this will trigger styles and they would be applied.
	//If you will move line below somewhere else it may cause that ContextMenu will behave differently from what you are expecting.
	_popup.Child = this;
	_popup.PlacementTarget = placementTarget;
	_popup.HorizontalOffset = HorizontalOffset;
	_popup.VerticalOffset = VerticalOffset;
	_popup.PlacementAnchor = PlacementAnchor;
	_popup.PlacementConstraintAdjustment = PlacementConstraintAdjustment;
	_popup.PlacementGravity = PlacementGravity;
	_popup.PlacementRect = PlacementRect;
	_popup.WindowManagerAddShadowHint = WindowManagerAddShadowHint;
	IsOpen = true;
	_popup.IsOpen = true;
	RaiseEvent(new RoutedEventArgs
	{
	RoutedEvent = OpenedEvent,
	Source = this,
	});
	}

From looking at the ContextMenu implementation it seems like the popup is closed when it's child ContextMenu is closed.

Avalonia/src/Avalonia.Controls/ContextMenu.cs

Lines 274 to 285 in bb6005b

	public override void Close()
	{
	if (!IsOpen)
	{
	return;
	}
	if (_popup != null && _popup.IsVisible)
	{
	_popup.IsOpen = false;
	}
	}