This answer uses a custom GridViewEx class inherited from GridView which allows the objective of reordering grouped rows using drag & drop to be achieved in a clean manner without a lot of code mixed in with the main form. Your post and additional comments state two requirements, and I have added a third goal to make the look and feel similar to the drag drop functionality that already exists for the records.
- Before or After Target Row
- Expanded rows stay expanded
- Drag feedback similar to record version
This custom version is simply swapped out manually in the Designer.cs file.
The feedback line in this example is blue for "Before Target Row" and red for "After Target Row".
Groups that are expanded before an operation remain in that state.
GridViewEx - The demo project is available to clone from GitHub.
GridViewEx maintains its own GroupDragDropState to avoid potential conflicts with BehaviorManager operations.
enum GroupDragDropState
{
None,
Down,
Drag,
Drop,
}
The Drag state is entered if the mouse-down cursor travels more than 10 positions in any direction.
internal class GridViewEx : GridView
{
public GridViewEx()
{
MouseDown += OnMouseDown;
MouseMove += OnMouseMove;
MouseUp += OnMouseUp;
CustomDrawGroupRow += OnCustomDrawGroupRow;
DataSourceChanged += OnDataSourceChanged;
DisableCurrencyManager = true; // Use this setting From sample code.
GroupRowCollapsing += OnGroupRowCollapsing;
CustomColumnSort += OnCustomColumnSort;
}
protected virtual void OnMouseDown(object sender, MouseEventArgs e)
{
var hittest = CalcHitInfo(e.Location);
var screenLocation = PointToScreen(e.Location);
_mouseDownClient = e.Location;
_isGroupRow = hittest.RowInfo != null && hittest.RowInfo.IsGroupRow;
if (_isGroupRow)
{
var gridGroupInfo = (GridGroupRowInfo)hittest.RowInfo;
_dragFeedbackLabel.RowBounds = hittest.RowInfo.Bounds.Size;
DragRowInfo = gridGroupInfo;
_isExpanded = gridGroupInfo.IsGroupRowExpanded;
}
}
protected virtual void OnMouseMove(object sender, MouseEventArgs e)
{
if (Control.MouseButtons.Equals(MouseButtons.Left))
{
_mouseDeltaX = _mouseDownClient.X - e.Location.X;
_mouseDeltaY = _mouseDownClient.Y - e.Location.Y;
if (Math.Abs(_mouseDeltaX) > 10 || Math.Abs(_mouseDeltaY) > 10)
{
GroupDragDropState = GroupDragDropState.Drag;
}
var hittest = CalcHitInfo(e.Location);
if ((hittest.RowInfo == null) || hittest.RowInfo.Equals(DragRowInfo) || !hittest.RowInfo.IsGroupRow)
{
CurrentGroupRowInfo = null;
}
else
{
CurrentGroupRowInfo = (GridGroupRowInfo)hittest.RowInfo;
var deltaY = e.Location.Y - CurrentGroupRowInfo.Bounds.Location.Y;
var mid = CurrentGroupRowInfo.Bounds.Height / 2;
DropBelow = deltaY >= mid;
}
}
}
protected virtual void OnMouseUp(object sender, MouseEventArgs e)
{
switch (GroupDragDropState)
{
case GroupDragDropState.None:
break;
case GroupDragDropState.Down:
GroupDragDropState = GroupDragDropState.None;
break;
case GroupDragDropState.Drag:
GroupDragDropState = GroupDragDropState.Drop;
break;
case GroupDragDropState.Drop:
GroupDragDropState = GroupDragDropState.None;
break;
}
}
private Point _mouseDownClient = Point.Empty;
private int _mouseDeltaX = 0;
private int _mouseDeltaY = 0;
.
.
.
}
Drag Feedback
Entering the drag state takes a screenshot of the clicked row. To ensure the proper operation of the Graphics.CopyFromScreen method, the appconfig.cs has been modified to per-screen DPI awareness.
appconfig.cs
<?xml version="1.0"?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8"/>
</startup>
<System.Windows.Forms.ApplicationConfigurationSection>
<add key="DpiAwareness" value="PerMonitorV2" />
</System.Windows.Forms.ApplicationConfigurationSection>
</configuration>
GridViewEx.cs
protected virtual void OnGroupDragDropStateChanged()
{
switch (GroupDragDropState)
{
case GroupDragDropState.None:
break;
case GroupDragDropState.Down:
break;
case GroupDragDropState.Drag:
if (_isGroupRow)
{
getRowScreenshot();
}
_dragFeedbackLabel.Visible = true;
break;
case GroupDragDropState.Drop:
_dragFeedbackLabel.Visible = false;
OnDrop();
break;
default:
break;
}
}
void getRowScreenshot()
{
// MUST be set to DPI AWARE in config.cs
var ctl = GridControl;
var screenRow = ctl.PointToScreen(DragRowInfo.Bounds.Location);
var screenParent = ctl.TopLevelControl.Location;
using (var srceGraphics = ctl.CreateGraphics())
{
var size = DragRowInfo.Bounds.Size;
var bitmap = new Bitmap(size.Width, size.Height, srceGraphics);
var destGraphics = Graphics.FromImage(bitmap);
destGraphics.CopyFromScreen(screenRow.X, screenRow.Y, 0, 0, size);
_dragFeedbackLabel.BackgroundImage = bitmap;
}
}
This image is assigned to the BackgroundImage of the _dragFeedbackLabel member which is a borderless form that can be drawn outside the rectangle of the main form. When visible, this form tracks the mouse cursor movement by means of a MessageFilter intercepting WM_MOUSEMOVE messages.
class DragFeedback : Form, IMessageFilter
{
const int WM_MOUSEMOVE = 0x0200;
public DragFeedback()
{
StartPosition = FormStartPosition.Manual;
FormBorderStyle = FormBorderStyle.None;
BackgroundImageLayout = ImageLayout.Stretch;
Application.AddMessageFilter(this);
Disposed += (sender, e) => Application.RemoveMessageFilter(this);
}
protected override void SetBoundsCore(int x, int y, int width, int height, BoundsSpecified specified)
{
if (RowBounds == null)
{
base.SetBoundsCore(x, y, width, height, specified);
}
else
{
base.SetBoundsCore(x, y, RowBounds.Width, RowBounds.Height, specified);
}
}
public bool PreFilterMessage(ref Message m)
{
if(MouseButtons == MouseButtons.Left && m.Msg.Equals(WM_MOUSEMOVE))
{
Location = MousePosition;
}
return false;
}
Point _mouseDownPoint = Point.Empty;
Point _origin = Point.Empty;
public Size RowBounds { get; internal set; }
public new Image BackgroundImage
{
get => base.BackgroundImage;
set
{
if((value == null) || (base.BackgroundImage == null))
{
base.BackgroundImage = value;
}
}
}
protected override void OnVisibleChanged(EventArgs e)
{
base.OnVisibleChanged(e);
if(!Visible)
{
base.BackgroundImage?.Dispose(); ;
base.BackgroundImage = null;
}
}
}
The row dividers are drawn by handling the GridView.CustomDrawGroupRow event.
protected virtual void OnCustomDrawGroupRow(object sender, RowObjectCustomDrawEventArgs e)
{
if (e.Info is GridRowInfo ri)
{
using (var pen = new Pen(DropBelow ? Brushes.LightSalmon : Brushes.Aqua, 4F))
{
switch (GroupDragDropState)
{
case GroupDragDropState.Drag:
if (CurrentGroupRowInfo != null)
{
if (ri.RowHandle == CurrentGroupRowInfo.RowHandle)
{
e.DefaultDraw();
int y;
if (DropBelow)
{
y = ri.Bounds.Y + CurrentGroupRowInfo.Bounds.Height - 2;
}
else
{
y = ri.Bounds.Y + 1;
}
e.Graphics.DrawLine(pen,
ri.Bounds.X, y,
ri.Bounds.X + ri.Bounds.Width, y);
e.Handled = true;
}
}
break;
}
}
}
}
When the DropBelow value toggles at the midpoint of the drag over or when the target row changes, the affected row(s) need to be redrawn.
public bool DropBelow
{
get => _dropBelow;
set
{
if (!Equals(_dropBelow, value))
{
_dropBelow = value;
#if true
// "Minimal redraw" version
RefreshRow(CurrentGroupRowInfo.RowHandle);
#else
// But if drawing artifacts are present, refresh
// the entire control surface instead.
GridControl.Refresh();
#endif
}
}
}
bool _dropBelow = false;
OnDrop
The ItemsArray for the removed records is stashed in a dictionary to allow reassignment before inserting the same DataRow instance at a new index. Adjustments to the insert operation are made depending on the value of the DropBelow boolean which was set in the MouseMove handler.
protected virtual void OnDrop()
{
var dataTable = (DataTable)GridControl.DataSource;
if (!((DragRowInfo == null) || (CurrentGroupRowInfo == null)))
{
Debug.WriteLine($"{DragRowInfo.GroupValueText} {CurrentGroupRowInfo.GroupValueText}");
var drags =
dataTable
.Rows
.Cast<DataRow>()
.Where(_ => _[CurrentGroupRowInfo.Column.FieldName]
.Equals(DragRowInfo.EditValue)).ToArray();
var dict = new Dictionary<DataRow, object[]>();
foreach (var dataRow in drags)
{
dict[dataRow] = dataRow.ItemArray;
dataTable.Rows.Remove(dataRow);
}
DataRow receiver =
dataTable
.Rows
.Cast<DataRow>()
.FirstOrDefault(_ =>
_[CurrentGroupRowInfo.Column.FieldName]
.Equals(CurrentGroupRowInfo.EditValue));
int insertIndex;
if (DropBelow)
{
receiver =
dataTable
.Rows
.Cast<DataRow>()
.LastOrDefault(_ =>
_[CurrentGroupRowInfo.Column.FieldName]
.Equals(CurrentGroupRowInfo.EditValue));
insertIndex = dataTable.Rows.IndexOf(receiver) + 1;
}
else
{
receiver =
dataTable
.Rows
.Cast<DataRow>()
.FirstOrDefault(_ =>
_[CurrentGroupRowInfo.Column.FieldName]
.Equals(CurrentGroupRowInfo.EditValue));
insertIndex = dataTable.Rows.IndexOf(receiver);
}
foreach (var dataRow in drags.Reverse())
{
dataRow.ItemArray = dict[dataRow];
dataTable.Rows.InsertAt(dataRow, insertIndex);
}
try
{
var parentRowHandle = GetParentRowHandle(insertIndex);
if (_isExpanded)
{
ExpandGroupRow(parentRowHandle);
}
FocusedRowHandle = parentRowHandle;
}
catch (Exception ex)
{
Debug.Assert(false, ex.Message);
}
}
}
Misc
GridViewEx takes a blanket approach to enabling custom sort only, and preliminary testing shows that drag drop in its present form works the same for the Keyword grouping as it does for Level.
/// <summary>
/// Disable automatic sorting.
/// </summary>
protected virtual void OnDataSourceChanged(object sender, EventArgs e)
{
foreach (GridColumn column in Columns)
{
column.SortMode = ColumnSortMode.Custom;
}
ExpandGroupLevel(1);
}
protected virtual void OnCustomColumnSort(object sender, CustomColumnSortEventArgs e)
{
e.Handled = true;
}
/// <summary>
/// Disallow collapses during drag operations
/// </summary>
protected virtual void OnGroupRowCollapsing(object sender, RowAllowEventArgs e)
{
e.Allow = GroupDragDropState.Equals(GroupDragDropState.None);
}
