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Merge pull request #392 from /issues/389
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Fix for drag preview doesn't show up if the source is not a target
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@punker76
punker76 authored Sep 7, 2021
2 parents a6647c1 + f6b712b commit d6994c8
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Showing 4 changed files with 306 additions and 92 deletions.
153 changes: 72 additions & 81 deletions src/GongSolutions.WPF.DragDrop/DragDrop.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,89 +14,64 @@ namespace GongSolutions.Wpf.DragDrop
{
public static partial class DragDrop
{
private static DragDropPreview GetDragDropPreview(DropInfo dropInfo, UIElement target)
internal static DataTemplate TryGetDragAdornerTemplate(UIElement source, UIElement sender)
{
var dragInfo = dropInfo.DragInfo;
var template = GetDropAdornerTemplate(dropInfo.VisualTarget) ?? GetDragAdornerTemplate(dragInfo.VisualSource);
var templateSelector = GetDropAdornerTemplateSelector(dropInfo.VisualTarget) ?? GetDragAdornerTemplateSelector(dragInfo.VisualSource);

UIElement adornment = null;

var useDefaultDragAdorner = template == null && templateSelector == null && GetUseDefaultDragAdorner(dragInfo.VisualSource);
var useVisualSourceItemSizeForDragAdorner = GetUseVisualSourceItemSizeForDragAdorner(dragInfo.VisualSource);

if (useDefaultDragAdorner)
var template = source is not null ? GetDragAdornerTemplate(source) : null;
if (template is null && sender is not null)
{
template = dragInfo.VisualSourceItem.GetCaptureScreenDataTemplate(dragInfo.VisualSourceFlowDirection);
template = GetDragAdornerTemplate(sender);
}

if (template != null || templateSelector != null)
{
if (dragInfo.Data is IEnumerable items && !(items is string))
{
var itemsCount = items.Cast<object>().Count();
var maxItemsCount = TryGetDragPreviewMaxItemsCount(dragInfo, target);
if (!useDefaultDragAdorner && itemsCount <= maxItemsCount)
{
var itemsControl = new ItemsControl();

// sort items if necessary before creating the preview
var sorter = TryGetDragPreviewItemsSorter(dragInfo, target);
if (sorter != null)
{
itemsControl.ItemsSource = sorter.SortDragPreviewItems(items);
}
else
{
itemsControl.ItemsSource = items;
}
return template;
}

itemsControl.ItemTemplate = template;
itemsControl.ItemTemplateSelector = templateSelector;
itemsControl.Tag = dragInfo;
internal static DataTemplateSelector TryGetDragAdornerTemplateSelector(UIElement source, UIElement sender)
{
var templateSelector = source is not null ? GetDragAdornerTemplateSelector(source) : null;
if (templateSelector is null && sender is not null)
{
templateSelector = GetDragAdornerTemplateSelector(sender);
}

if (useVisualSourceItemSizeForDragAdorner)
{
var bounds = VisualTreeExtensions.GetVisibleDescendantBounds(dragInfo.VisualSourceItem);
itemsControl.SetValue(FrameworkElement.MinWidthProperty, bounds.Width);
}
return templateSelector;
}

// The ItemsControl doesn't display unless we create a grid to contain it.
// Not quite sure why we need this...
var grid = new Grid();
grid.Children.Add(itemsControl);
adornment = grid;
}
}
else
{
var contentPresenter = new ContentPresenter();
contentPresenter.Content = dragInfo.Data;
contentPresenter.ContentTemplate = template;
contentPresenter.ContentTemplateSelector = templateSelector;
contentPresenter.Tag = dragInfo;
internal static DataTemplate TryGetDropAdornerTemplate(UIElement source, UIElement sender)
{
var template = source is not null ? GetDropAdornerTemplate(source) : null;
if (template is null && sender is not null)
{
template = GetDropAdornerTemplate(sender);
}

if (useVisualSourceItemSizeForDragAdorner)
{
var bounds = VisualTreeExtensions.GetVisibleDescendantBounds(dragInfo.VisualSourceItem);
contentPresenter.SetValue(FrameworkElement.MinWidthProperty, bounds.Width);
contentPresenter.SetValue(FrameworkElement.MinHeightProperty, bounds.Height);
}
return template;
}

adornment = contentPresenter;
}
internal static DataTemplateSelector TryGetDropAdornerTemplateSelector(UIElement source, UIElement sender)
{
var templateSelector = source is not null ? GetDropAdornerTemplateSelector(source) : null;
if (templateSelector is null && sender is not null)
{
templateSelector = GetDropAdornerTemplateSelector(sender);
}

if (adornment != null)
return templateSelector;
}

private static DragDropPreview GetDragDropPreview(IDragInfo dragInfo, UIElement visualTarget, UIElement sender)
{
var visualSource = dragInfo?.VisualSource;
if (visualSource is null)
{
if (useDefaultDragAdorner)
{
adornment.Opacity = GetDefaultDragAdornerOpacity(dragInfo.VisualSource);
}
return null;
}

var rootElement = TryGetRootElementFinder(target).FindRoot(dropInfo.VisualTarget ?? dragInfo.VisualSource);
var rootElement = TryGetRootElementFinder(sender).FindRoot(visualTarget ?? visualSource);

var preview = new DragDropPreview(rootElement, adornment, GetDragAdornerTranslation(dragInfo.VisualSource), GetDragMouseAnchorPoint(dragInfo.VisualSource)) { IsOpen = true };
var preview = new DragDropPreview(rootElement, dragInfo, visualTarget ?? visualSource, sender);
if (preview.Child != null)
{
preview.IsOpen = true;
return preview;
}

Expand All @@ -106,22 +81,26 @@ private static DragDropPreview GetDragDropPreview(DropInfo dropInfo, UIElement t
private static DragDropEffectPreview GetDragDropEffectPreview(DropInfo dropInfo, UIElement sender)
{
var dragInfo = dropInfo.DragInfo;
var template = GetDragDropEffecTemplate(dragInfo.VisualSource, dropInfo);
var template = GetDragDropEffectTemplate(dragInfo.VisualSource, dropInfo);

if (template != null)
{
var rootElement = TryGetRootElementFinder(sender).FindRoot(dropInfo.VisualTarget ?? dragInfo.VisualSource);

var adornment = new ContentPresenter { Content = dragInfo.Data, ContentTemplate = template };

var preview = new DragDropEffectPreview(rootElement, adornment, GetEffectAdornerTranslation(dragInfo.VisualSource), dropInfo.Effects, dropInfo.EffectText, dropInfo.DestinationText) { IsOpen = true };
var preview = new DragDropEffectPreview(rootElement, adornment, GetEffectAdornerTranslation(dragInfo.VisualSource), dropInfo.Effects, dropInfo.EffectText, dropInfo.DestinationText)
{
IsOpen = true
};

return preview;
}

return null;
}

private static DataTemplate GetDragDropEffecTemplate(UIElement target, DropInfo dropInfo)
private static DataTemplate GetDragDropEffectTemplate(UIElement target, DropInfo dropInfo)
{
if (target is null)
{
Expand Down Expand Up @@ -303,7 +282,7 @@ private static IRootElementFinder TryGetRootElementFinder(UIElement sender)
return rootElementFinder ?? DefaultRootElementFinder;
}

private static int TryGetDragPreviewMaxItemsCount(IDragInfo dragInfo, UIElement sender)
internal static int TryGetDragPreviewMaxItemsCount(IDragInfo dragInfo, UIElement sender)
{
var itemsCount = dragInfo?.VisualSource != null ? GetDragPreviewMaxItemsCount(dragInfo.VisualSource) : -1;
if (itemsCount < 0 && sender != null)
Expand All @@ -314,7 +293,7 @@ private static int TryGetDragPreviewMaxItemsCount(IDragInfo dragInfo, UIElement
return itemsCount < 0 || itemsCount >= int.MaxValue ? 10 : itemsCount;
}

private static IDragPreviewItemsSorter TryGetDragPreviewItemsSorter(IDragInfo dragInfo, UIElement sender)
internal static IDragPreviewItemsSorter TryGetDragPreviewItemsSorter(IDragInfo dragInfo, UIElement sender)
{
var itemsSorter = dragInfo?.VisualSource != null ? GetDragPreviewItemsSorter(dragInfo.VisualSource) : null;
if (itemsSorter is null && sender != null)
Expand Down Expand Up @@ -490,7 +469,7 @@ private static void DragSourceOnTouchMove(object sender, TouchEventArgs e)
return;
}

DoDragSourceMove(sender, e.GetTouchPoint((IInputElement)sender).Position);
DoDragSourceMove(sender, element => e.GetTouchPoint(element).Position);
}
}

Expand All @@ -512,11 +491,11 @@ private static void DragSourceOnMouseMove(object sender, MouseEventArgs e)
return;
}

DoDragSourceMove(sender, e.GetPosition((IInputElement)sender));
DoDragSourceMove(sender, element => e.GetPosition(element));
}
}

private static void DoDragSourceMove(object sender, Point position)
private static void DoDragSourceMove(object sender, Func<IInputElement, Point> getPosition)
{
var dragInfo = _dragInfo;
if (dragInfo != null && !_dragInProgress)
Expand All @@ -528,6 +507,7 @@ private static void DoDragSourceMove(object sender, Point position)
dragInfo.VisualSource?.ReleaseMouseCapture();

// only if the sender is the source control and the mouse point differs from an offset
var position = getPosition((IInputElement)sender);
if (dragInfo.VisualSource == sender
&& (Math.Abs(position.X - dragStart.X) > DragDrop.GetMinimumHorizontalDragDistance(dragInfo.VisualSource) ||
Math.Abs(position.Y - dragStart.Y) > DragDrop.GetMinimumVerticalDragDistance(dragInfo.VisualSource)))
Expand Down Expand Up @@ -561,6 +541,12 @@ private static void DoDragSourceMove(object sender, Point position)
{
_dragInProgress = true;

if (DragDropPreview is null)
{
DragDropPreview = GetDragDropPreview(dragInfo, null, sender as UIElement);
DragDropPreview?.Move(getPosition(DragDropPreview.PlacementTarget));
}

hookId = MouseHelper.HookMouseMove(point =>
{
DragDropPreview?.Move(CursorHelper.GetCurrentCursorPosition(DragDropPreview.PlacementTarget, point));
Expand Down Expand Up @@ -659,10 +645,15 @@ private static void DropTargetOnDragOver(object sender, DragEventArgs e, EventTy

dropHandler.DragOver(dropInfo);

if (DragDropPreview is null && dragInfo is { })
if (dragInfo is not null)
{
DragDropPreview = GetDragDropPreview(dropInfo, sender as UIElement);
DragDropPreview?.Move(e.GetPosition(DragDropPreview.PlacementTarget));
if (DragDropPreview is null)
{
DragDropPreview = GetDragDropPreview(dragInfo, dropInfo.VisualTarget, sender as UIElement);
DragDropPreview?.Move(e.GetPosition(DragDropPreview.PlacementTarget));
}

DragDropPreview?.UpdatePreviewPresenter(dragInfo, dropInfo.VisualTarget, sender as UIElement);
}

Scroll(dropInfo, e);
Expand Down Expand Up @@ -736,7 +727,7 @@ private static void DropTargetOnDragOver(object sender, DragEventArgs e, EventTy
DragDropEffectPreview.EffectText = dropInfo.EffectText;
DragDropEffectPreview.DestinationText = dropInfo.DestinationText;

var template = GetDragDropEffecTemplate(dragInfo.VisualSource, dropInfo);
var template = GetDragDropEffectTemplate(dragInfo.VisualSource, dropInfo);
if (template is null)
{
DragDropEffectPreview = null;
Expand Down
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