feature<NewPage>: show drop area border while dragging items in/into repositories' tree

src/App.preference.cs

@@ -200,6 +200,7 @@ namespace SourceGit {
         /// <returns></returns>
         public bool IsSubGroup(string parentId, string subId) {
             if (string.IsNullOrEmpty(parentId)) return false;
+            if (parentId == subId) return true;
 
             var g = FindGroup(subId);
             if (g == null) return false;

src/Helpers/TreeViewHelper.cs

@@ -254,7 +254,7 @@ namespace SourceGit.Helpers {
         /// <param name="item"></param>
         /// <param name="child"></param>
         /// <returns></returns>
-        private static TreeViewItem FindTreeViewItem(DependencyObject child) {
+        public static TreeViewItem FindTreeViewItem(DependencyObject child) {
             if (child == null) return null;
             if (child is TreeViewItem) return child as TreeViewItem;
             if (child is TreeView) return null;

src/UI/NewPage.xaml

@@ -16,7 +16,7 @@
         <converters:InverseBool x:Key="InverseBool"/>
     </UserControl.Resources>
 
-    <Grid>
+    <Grid AllowDrop="True" DragEnter="PageDragEnter" DragLeave="PageDragLeave" Drop="PageDrop" Background="Transparent">
         <!-- Main Body -->
         <Grid HorizontalAlignment="Center" MinWidth="420" TextElement.FontFamily="Consolas">
             <Grid.RowDefinitions>
@@ -58,7 +58,7 @@
             <!-- Horizontal Line -->
             <Rectangle Grid.Row="3" Height="1" Fill="{StaticResource Brush.Border1}"/>
 
-            <!-- Repositories' tree -->
+            <!-- Group Title For Repositories -->
             <Grid Grid.Row="4" Margin="0,8,0,0">
                 <Grid.ColumnDefinitions>
                     <ColumnDefinition Width="Auto"/>
@@ -69,25 +69,37 @@
                 <TextBlock Grid.Column="0" Text="REPOSITORIES" FontSize="18" FontWeight="ExtraBold" Foreground="{StaticResource Brush.FG2}"/>
                 <TextBlock Grid.Column="2" Text="DRAG-DROP YOUR FOLDER" FontSize="14" Foreground="{StaticResource Brush.FG2}" VerticalAlignment="Center"/>
             </Grid>
+
+            <!-- Drop area tip. -->
+            <Rectangle 
+                Grid.Row="5" 
+                x:Name="dropArea" 
+                Margin="0,2" 
+                Stroke="{StaticResource Brush.Border1}" 
+                StrokeThickness="2" 
+                StrokeDashArray="4 4"
+                Visibility="Hidden"
+                SnapsToDevicePixels="True"/>
+
+            <!-- Repository Tree -->
             <TreeView
                 x:Name="repositories"
                 Grid.Row="5"
-                Margin="0,4"
+                Margin="2,4"
                 Padding="0"
                 AllowDrop="True"
                 TextElement.FontSize="14"
                 ScrollViewer.HorizontalScrollBarVisibility="Disabled"
                 ContextMenuOpening="TreeContextMenuOpening"
-                Drop="TreeDrop" 
-                MouseMove="TreeMouseMove">
+                MouseMove="TreeMouseMove"
+                DragOver="TreeDragOver"
+                DragEnter="TreeDragEnter"
+                Drop="TreeDrop">
 
                 <TreeView.ItemContainerStyle>
                     <Style TargetType="{x:Type TreeViewItem}" BasedOn="{StaticResource Style.TreeView.ItemContainerStyle}">
                         <Setter Property="IsExpanded" Value="{Binding IsExpended, Mode=TwoWay}"/>
-                        <Setter Property="AllowDrop" Value="{Binding IsRepo, Converter={StaticResource InverseBool}}"/>
 
-                        <EventSetter Event="DragOver" Handler="TreeNodeDragOver"/>
-                        <EventSetter Event="Drop" Handler="TreeNodeDrop"/>
                         <EventSetter Event="Expanded" Handler="TreeNodeIsExpandedChanged"/>
                         <EventSetter Event="Collapsed" Handler="TreeNodeIsExpandedChanged"/>
                         <EventSetter Event="KeyDown" Handler="TreeNodeKeyDown"/>
@@ -98,7 +110,8 @@
 
                 <TreeView.ItemTemplate>                    
                     <HierarchicalDataTemplate ItemsSource="{Binding Children}">
-                        <Grid Height="32">
+                        <Border Height="32">
+                            <Grid IsHitTestVisible="False">
                                 <Grid.ColumnDefinitions>
                                     <ColumnDefinition Width="Auto"/>
                                     <ColumnDefinition Width="*"/>
@@ -150,6 +163,7 @@
                                     Fill="{Binding Color, Converter={StaticResource IntToRepoColor}}" 
                                     Visibility="{Binding IsRepo, Converter={StaticResource BoolToCollapsed}}"/>
                             </Grid>
+                        </Border>
 
                         <HierarchicalDataTemplate.Triggers>
                             <DataTrigger Binding="{Binding IsExpended}" Value="True">

src/UI/NewPage.xaml.cs

@@ -61,6 +61,93 @@ namespace SourceGit.UI {
         }
         #endregion
 
+        #region EVENT_DRAG_DROP
+        private void PageDragEnter(object sender, DragEventArgs e) {
+            if (e.Data.GetDataPresent(DataFormats.FileDrop)) {
+                if (!MakeSureReady()) return;
+                SetDragAreaVisibility(true);
+            }
+        }
+
+        private void PageDragLeave(object sender, DragEventArgs e) {
+            SetDragAreaVisibility(false);
+        }
+
+        private void PageDrop(object sender, DragEventArgs e) {
+            SetDragAreaVisibility(false);
+        }
+
+        private void TreeMouseMove(object sender, MouseEventArgs e) {
+            if (e.LeftButton != MouseButtonState.Pressed) return;
+
+            if (repositories.SelectedItem != null) {
+                DragDrop.DoDragDrop(repositories, repositories.SelectedItem, DragDropEffects.Move);
+            }
+            
+            e.Handled = true;
+        }
+
+        private void TreeDragEnter(object sender, DragEventArgs e) {
+            SetDragAreaVisibility(true);
+        }
+
+        private void TreeDragOver(object sender, DragEventArgs e) {
+            var dropToItem = Helpers.TreeViewHelper.FindTreeViewItem(e.OriginalSource as DependencyObject);
+            if (dropToItem != null) {
+                var node = dropToItem.DataContext as Node;
+                if (!node.IsRepo && !node.IsExpended) dropToItem.IsExpanded = true;
+            }
+        }
+
+        private void TreeDrop(object sender, DragEventArgs e) {
+            bool needRebuild = false;
+            SetDragAreaVisibility(false);
+
+            if (e.Data.GetDataPresent(DataFormats.FileDrop)) {
+                if (!MakeSureReady()) return;
+
+                string[] paths = e.Data.GetData(DataFormats.FileDrop) as string[];
+                string group = "";
+
+                var dropToItem = Helpers.TreeViewHelper.FindTreeViewItem(e.OriginalSource as DependencyObject);
+                if (dropToItem != null) {
+                    var parentNode = dropToItem.DataContext as Node;
+                    group = parentNode.IsRepo ? parentNode.ParentId : parentNode.Id;
+                }
+
+                foreach (var path in paths) {
+                    FileInfo info = new FileInfo(path);
+                    if (info.Attributes == FileAttributes.Directory && Git.Repository.IsValid(path)) {
+                        App.Setting.AddRepository(path, group);
+                        needRebuild = true;
+                    }
+                }
+            } else if (e.Data.GetDataPresent(typeof(Node))) {
+                var node = e.Data.GetData(typeof(Node)) as Node;
+                if (node == null) return;
+
+                string newParent = "";
+
+                var dropToItem = Helpers.TreeViewHelper.FindTreeViewItem(e.OriginalSource as DependencyObject);
+                if (dropToItem != null) {
+                    var newParentNode = dropToItem.DataContext as Node; 
+                    newParent = newParentNode.IsRepo ? newParentNode.ParentId : newParentNode.Id;
+                }
+
+                if (node.IsRepo) {
+                    App.Setting.FindRepository(node.Id).GroupId = newParent;
+                } else if (!App.Setting.IsSubGroup(node.Id, newParent)) {
+                    App.Setting.FindGroup(node.Id).ParentId = newParent;
+                }
+
+                needRebuild = true;
+            }
+
+            if (needRebuild) UpdateTree();
+            e.Handled = true;
+        }
+        #endregion
+
         #region EVENT_TREEVIEW
         private void TreeContextMenuOpening(object sender, ContextMenuEventArgs e) {
             var addFolder = new MenuItem();
@@ -77,54 +164,6 @@ namespace SourceGit.UI {
             e.Handled = true;
         }
 
-        private void TreeMouseMove(object sender, MouseEventArgs e) {
-            if (e.LeftButton != MouseButtonState.Pressed) return;
-            if (repositories.SelectedItem == null) return;
-            DragDrop.DoDragDrop(repositories, repositories.SelectedItem, DragDropEffects.Move);
-            e.Handled = true;
-        }
-
-        private void TreeDrop(object sender, DragEventArgs e) {
-            bool needRebuild = false;
-
-            if (e.Data.GetDataPresent(DataFormats.FileDrop)) {
-                if (!MakeSureReady()) return;
-
-                string[] paths = e.Data.GetData(DataFormats.FileDrop) as string[];
-                string group = "";
-
-                var node = (sender as TreeViewItem)?.DataContext as Node;
-                if (node != null) group = node.IsRepo ? node.ParentId : node.Id;
-
-                foreach (var path in paths) {
-                    FileInfo info = new FileInfo(path);
-                    if (info.Attributes == FileAttributes.Directory && Git.Repository.IsValid(path)) {
-                        App.Setting.AddRepository(path, group);
-                        needRebuild = true;
-                    }
-                }
-            } else if (e.Data.GetDataPresent(typeof(Node))) {
-                var node = e.Data.GetData(typeof(Node)) as Node;
-                if (node == null) return;
-
-                var to = (sender as TreeViewItem)?.DataContext as Node;
-                var parent = to != null ? to.Id : "";
-
-                if (node.IsRepo) {
-                    App.Setting.FindRepository(node.Id).GroupId = to != null ? to.Id : "";
-                } else if (!App.Setting.IsSubGroup(node.Id, parent)) {
-                    App.Setting.FindGroup(node.Id).ParentId = parent;
-                }
-
-                needRebuild = true;
-            }
-
-            if (needRebuild) UpdateTree();
-            e.Handled = true;
-        }
-        #endregion
-
-        #region EVENT_TREEVIEWITEM
         private void TreeNodeDoubleClick(object sender, MouseButtonEventArgs e) {
             var node = (sender as TreeViewItem).DataContext as Node;
             if (node != null && node.IsRepo) {
@@ -133,17 +172,6 @@ namespace SourceGit.UI {
             }
         }
 
-        private void TreeNodeDragOver(object sender, DragEventArgs e) {
-            var item = sender as TreeViewItem;
-            var node = item.DataContext as Node;
-            if (node != null && !node.IsRepo) item.IsExpanded = true;
-            e.Handled = true;
-        }
-
-        private void TreeNodeDrop(object sender, DragEventArgs e) {
-            TreeDrop(sender, e);
-        }
-
         private void TreeNodeIsExpandedChanged(object sender, RoutedEventArgs e) {
             var item = sender as TreeViewItem;
             var node = item.DataContext as Node;
@@ -390,6 +418,14 @@ namespace SourceGit.UI {
 
             UpdateTree();
         }
+
+        /// <summary>
+        ///     Set visibility of drag-drop area.
+        /// </summary>
+        /// <param name="bVisible"></param>
+        private void SetDragAreaVisibility(bool bVisible = true) {
+            dropArea.Visibility = bVisible ? Visibility.Visible : Visibility.Hidden;
+        }
         #endregion
     }
 }