/// <summary>
/// Starts a drag operation.
/// </summary>
/// <param name="floatWindow">The <see cref="FloatWindow"/> to be dragged.</param>
/// <param name="dockTabPane">The <see cref="DockTabPane"/> to be dragged.</param>
/// <param name="dockTabItem">The <see cref="DockTabItem"/> to be dragged.</param>
/// <returns>
/// <see langword="true" /> if the drag operation has been started; otherwise,
/// <see langword="false" /> if the drag operation could not be started (e.g. because the
/// mouse could not be captured).
/// </returns>
private bool BeginDrag(FloatWindow floatWindow, DockTabPane dockTabPane, DockTabItem dockTabItem)
{
_dockStrategy = _dockControl.GetViewModel()?.DockStrategy;
if (_dockStrategy == null || _dockStrategy.DockControl.IsLocked)
{
Reset();
return(false);
}
FrameworkElement element = null;
IDockTabPane draggedPane = null;
IDockTabItem draggedItem = null;
if (floatWindow != null)
{
// User is dragging a FloatWindow.
// (Note: Dragging of FloatWindows with nested layouts is not supported.)
draggedPane = floatWindow.GetViewModel()?.RootPane as IDockTabPane;
element = floatWindow;
_floatWindow = floatWindow;
_initialSize = floatWindow.RenderSize;
// Start dragging immediately.
_dragDeltaExceeded = true;
}
else if (dockTabItem != null)
{
// User is dragging a DockTabItem in a DockTabPanel.
draggedItem = dockTabItem.GetViewModel();
element = dockTabItem;
_targetDockTabPane = dockTabPane;
_initialSize = dockTabPane.RenderSize;
// Start dragging when threshold is exceeded.
_initialMousePosition = WindowsHelper.GetMousePosition(_dockControl);
_dragDeltaExceeded = false;
}
else if (dockTabPane != null)
{
// User is dragging a DockTabPane.
draggedPane = dockTabPane.GetViewModel();
element = dockTabPane;
_initialSize = dockTabPane.RenderSize;
_initialMousePosition = WindowsHelper.GetMousePosition(_dockControl);
// Start dragging when threshold is exceeded.
_initialMousePosition = WindowsHelper.GetMousePosition(_dockControl);
_dragDeltaExceeded = false;
}
if (draggedPane == null && draggedItem == null)
{
Reset();
return(false);
}
// When the user is dragging the FloatWindow, the mouse is captured by Win32 move window
// loop. When dragging a DockTabPane or DockTabItem, the mouse needs to be
// captured to receive mouse events.
if (_floatWindow == null)
{
if (!_dockControl.CaptureMouse())
{
// Failed to capture the mouse.
Reset();
return(false);
}
_dockControl.LostMouseCapture += OnLostMouseCapture;
_dockControl.MouseLeftButtonUp += OnMouseLeftButtonUp;
_dockControl.MouseMove += OnMouseMove;
_dockControl.PreviewKeyDown += OnPreviewKeyDown;
if (_targetDockTabPane != null)
{
_targetDockTabPane.PreviewKeyDown += OnPreviewKeyDown;
}
}
_dockStrategy.Begin();
if (draggedPane != null)
{
_dockStrategy.Activate(draggedPane);
_activeItem = draggedPane.SelectedItem;
foreach (var item in draggedPane.Items)
{
if (item.DockState == draggedPane.DockState)
{
_draggedItems.Add(item);
}
}
}
else
{
Debug.Assert(draggedItem != null);
_dockStrategy.Activate(draggedItem);
_activeItem = draggedItem;
_draggedItems.Add(draggedItem);
}
Debug.Assert(_draggedItems.Count > 0);
// Determine whether dragged items may end in a FloatWindow.
_canFloat = CanFloat();
// Store the mouse offset relative to the dragged element.
_mouseOffset = (Vector)WindowsHelper.GetMousePosition(element);
// Remember information needed for a rollback.
ReplaceItemsWithProxies(draggedPane ?? _targetDockTabPane.GetViewModel());
_originalDockState = _draggedItems[0].DockState;
BackupFloatWindowPosition();
// Override mouse cursors. (Mouse cursor should not change to caret over text editor.)
Mouse.OverrideCursor = Cursors.Arrow;
return(true);
}