ToolStripDropTargetManager.cs source code in C# .NET

                        Code:
                         / FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / WinForms / Managed / System / WinForms / ToolStripDropTargetManager.cs / 1 / ToolStripDropTargetManager.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

 
namespace System.Windows.Forms { 
    using System;
    using System.ComponentModel; 
    using System.Drawing;
    using System.Diagnostics;
    using System.Threading;
    using System.Runtime.InteropServices; 
    using System.Security;
    using System.Globalization; 
 
    /// 
    /// Why do we have this class?  Well it seems that RegisterDropTarget 
    /// requires an HWND to back it's IDropTargets.  Since some ToolStripItems
    /// do not have HWNDS, this guy's got to figure out who the event was
    /// really supposed to go to and pass it on to it.
    ///  
    internal class ToolStripDropTargetManager : IDropTarget {
 	 
        private IDropTarget lastDropTarget; 
        private ToolStrip owner;
 
#if DEBUG
        private bool dropTargetIsEntered;
#endif
 

#if DEBUG 
        internal static readonly TraceSwitch DragDropDebug = new TraceSwitch("DragDropDebug", "Debug ToolStrip DragDrop code"); 
#else
        internal static readonly TraceSwitch DragDropDebug; 
#endif

        /// 
        /// Summary of ToolStripDropTargetManager. 
        /// 
        /// 	 
        public ToolStripDropTargetManager(ToolStrip owner) { 
            this.owner = owner;
            if (owner == null) { 
                throw new ArgumentNullException("owner");
            }
        }
 
        /// 
        /// Summary of EnsureRegistered. 
        ///  
        /// 	
        public void EnsureRegistered(IDropTarget dropTarget) { 
            Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Ensuring drop target registered");
            SetAcceptDrops(true);	
        }
 
        /// 
        /// Summary of EnsureUnRegistered. 
        ///  
        /// 	
        public void EnsureUnRegistered(IDropTarget dropTarget) { 

            Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Attempting to unregister droptarget");
            for (int i = 0; i < owner.Items.Count; i++) {
                if (owner.Items[i].AllowDrop) { 
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "An item still has allowdrop set to true - cant unregister");
                    return; // can't unregister this as a drop target unless everyone is done.			 
                } 
            }
            if (owner.AllowDrop || owner.AllowItemReorder) { 
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "The ToolStrip has AllowDrop or AllowItemReorder set to true - cant unregister");
                return;  // can't unregister this as a drop target if ToolStrip is still accepting drops
            }
		 
            SetAcceptDrops(false);
            owner.DropTargetManager = null; 
        } 

        ///  
        /// Takes a screen point and converts it into an item. May return null.
        /// 
        /// 
        /// 	 
        private ToolStripItem FindItemAtPoint(int x, int y) {
            return owner.GetItemAt(owner.PointToClient(new Point(x,y))); 
        }	 
        /// 
        /// Summary of OnDragEnter. 
        /// 
        /// 	
        public void OnDragEnter(DragEventArgs e) {
			Debug.WriteLineIf(DragDropDebug.TraceVerbose, "[DRAG ENTER] =============="); 

            // If we are supporting Item Reordering 
            // and this is a ToolStripItem - snitch it. 
            if (owner.AllowItemReorder && e.Data.GetDataPresent(typeof(ToolStripItem))) {
            	Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ItemReorderTarget taking this..."); 
                lastDropTarget = owner.ItemReorderDropTarget;

            }
            else { 
                ToolStripItem item = FindItemAtPoint(e.X, e.Y);
 
                if ((item != null) && (item.AllowDrop)) { 
                    // the item wants this event
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ToolStripItem taking this: " + item.ToString()); 

                    lastDropTarget = ((IDropTarget)item);				
                }
                else if (owner.AllowDrop) { 
                    // the winbar wants this event
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ToolStrip taking this because AllowDrop set to true."); 
                    lastDropTarget = ((IDropTarget)owner); 

                }	 
                else {
                    // There could be one item that says "AllowDrop == true" which would turn
                    // on this drop target manager.  If we're not over that particular item - then
                    // just null out the last drop target manager. 

                    // the other valid reason for being here is that we've done an AllowItemReorder 
                    // and we dont have a ToolStripItem contain within the data (say someone drags a link 
                    // from IE over the ToolStrip)
 
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "No one wanted it.");

                    lastDropTarget = null;
 
                }		
            } 
            if (lastDropTarget != null) { 
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Calling OnDragEnter on target...");
#if DEBUG 
                dropTargetIsEntered=true;
#endif
                lastDropTarget.OnDragEnter(e);
            } 
        }
 
        ///  
        /// Summary of OnDragOver.
        ///  
        /// 	
        public void OnDragOver(DragEventArgs e) {

	        Debug.WriteLineIf(DragDropDebug.TraceVerbose, "[DRAG OVER] =============="); 

            IDropTarget newDropTarget = null; 
 
            // If we are supporting Item Reordering
            // and this is a ToolStripItem - snitch it. 
            if (owner.AllowItemReorder && e.Data.GetDataPresent(typeof(ToolStripItem))) {
               	Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ItemReorderTarget taking this...");
                newDropTarget = owner.ItemReorderDropTarget;
            } 
            else {
                ToolStripItem item = FindItemAtPoint(e.X, e.Y); 
 
                if ((item != null) && (item.AllowDrop)) {
                    // the item wants this event 
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ToolStripItem taking this: " + item.ToString());
                    newDropTarget = ((IDropTarget)item);				
                }
                else if (owner.AllowDrop) { 
                    // the winbar wants this event
                    Debug.WriteLineIf(DragDropDebug.TraceVerbose, "ToolStrip taking this because AllowDrop set to true."); 
                    newDropTarget = ((IDropTarget)owner); 
                }	
                else { 
 					Debug.WriteLineIf(DragDropDebug.TraceVerbose, "No one wanted it.");
                    newDropTarget = null;
                }		
            } 

            // if we've switched drop targets - then 
            // we need to create drag enter and leave events 
            if (newDropTarget != lastDropTarget) {
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "NEW DROP TARGET!"); 
                UpdateDropTarget(newDropTarget, e);
            }

            // now call drag over 
            if (lastDropTarget != null) {
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Calling OnDragOver on target..."); 
                lastDropTarget.OnDragOver(e); 
            }
				 
        }

        /// 
        /// Summary of OnDragLeave. 
        /// 
        /// 	 
        public void OnDragLeave(System.EventArgs e) { 
            Debug.WriteLineIf(DragDropDebug.TraceVerbose, "[DRAG LEAVE] ==============");
 
            if (lastDropTarget != null) {
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Calling OnDragLeave on current target...");
#if DEBUG
                dropTargetIsEntered=false; 
#endif
                lastDropTarget.OnDragLeave(e); 
 
            }
#if DEBUG 
            else {
                Debug.Assert(!dropTargetIsEntered, "Why do we have an entered droptarget and NO lastDropTarget?");
            }
#endif 
            lastDropTarget = null;
        } 
 
        /// 
        /// Summary of OnDragDrop. 
        /// 
        /// 	
        public void OnDragDrop(DragEventArgs e) {
            Debug.WriteLineIf(DragDropDebug.TraceVerbose, "[DRAG DROP] =============="); 

            if (lastDropTarget != null) { 
                Debug.WriteLineIf(DragDropDebug.TraceVerbose, "Calling OnDragDrop on current target..."); 

                lastDropTarget.OnDragDrop(e); 
            }
            else {
                Debug.Assert(false, "Why is lastDropTarget null?");
            } 
 	
            lastDropTarget = null;		 
        } 

 
        /// 
        ///     Used to actually register the control as a drop target.
        /// 
        ///  
        /// 	
        private void SetAcceptDrops(bool accept) { 
             if (owner.AllowDrop && accept) { 
                // if the owner has set AllowDrop to true then demand Clipboard permissions.
                // else its us, and we can assert them. 
                IntSecurity.ClipboardRead.Demand();
             }

 
             if (accept && owner.IsHandleCreated) {
                 try 
                 { 
                     if (Application.OleRequired() != System.Threading.ApartmentState.STA)
                     { 
                         throw new ThreadStateException(SR.GetString(SR.ThreadMustBeSTA));
                     }
                     if (accept)
                     { 
                         Debug.WriteLineIf(CompModSwitches.DragDrop.TraceInfo, "Registering as drop target: " + owner.Handle.ToString());
                         // Register 
                         int n = UnsafeNativeMethods.RegisterDragDrop(new HandleRef(owner, owner.Handle), (UnsafeNativeMethods.IOleDropTarget)(new DropTarget(this))); 

                         Debug.WriteLineIf(CompModSwitches.DragDrop.TraceInfo, "   ret:" + n.ToString(CultureInfo.InvariantCulture)); 
                         if (n != 0 && n != NativeMethods.DRAGDROP_E_ALREADYREGISTERED)
                         {
                             throw new Win32Exception(n);
                         } 
                     }
                     else 
                     { 
                         IntSecurity.ClipboardRead.Assert();
                         try 
                         {
                             Debug.WriteLineIf(CompModSwitches.DragDrop.TraceInfo, "Revoking drop target: " + owner.Handle.ToString());

                             // Revoke 
                             int n = UnsafeNativeMethods.RevokeDragDrop(new HandleRef(owner, owner.Handle));
                             Debug.WriteLineIf(CompModSwitches.DragDrop.TraceInfo, "   ret:" + n.ToString(CultureInfo.InvariantCulture)); 
                             if (n != 0 && n != NativeMethods.DRAGDROP_E_NOTREGISTERED) 
                             {
                                 throw new Win32Exception(n); 
                             }
                         }
                         finally
                         { 
                             CodeAccessPermission.RevertAssert();
                         } 
                     } 
                 }
                 catch (Exception e) 
                 {
                     throw new InvalidOperationException(SR.GetString(SR.DragDropRegFailed), e);
                 }
            } 
        }
 
        ///  
        /// if we have a new active item, fire drag leave and
        /// enter.  This corresponds to the case where you 
        /// are dragging between items and havent actually
        /// left the ToolStrip's client area.
        /// 
        ///  
        /// 	
        private void UpdateDropTarget(IDropTarget newTarget, DragEventArgs e) { 
 		 
            if (newTarget != lastDropTarget) {
 
                // tell the last drag target you've left
                if (lastDropTarget != null) {
                    OnDragLeave(new EventArgs());
                } 
                lastDropTarget = newTarget;
                if (newTarget != null) { 
                    DragEventArgs dragEnterArgs = new DragEventArgs(e.Data, e.KeyState, e.X, e.Y, e.AllowedEffect, e.Effect); 
                    dragEnterArgs.Effect = DragDropEffects.None;
 
                    // tell the next drag target you've entered
                    OnDragEnter(dragEnterArgs);
                }
            } 

        } 
 

 
    }

}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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ToolStripDropTargetManager.cs source code in C# .NET

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