Enable Drag and Drop support for OutlineView

OutlineView/OutlineView/AppDelegate.h

@@ -7,7 +7,7 @@
 
 #import <Cocoa/Cocoa.h>
 
-@interface AppDelegate : NSObject <NSApplicationDelegate, NSOutlineViewDelegate>
+@interface AppDelegate : NSObject <NSApplicationDelegate, NSOutlineViewDelegate, NSOutlineViewDataSource>
 
 @property (assign) IBOutlet NSWindow *window;
 

OutlineView/OutlineView/AppDelegate.m

@@ -21,12 +21,16 @@ @implementation AppDelegate
 - (void)applicationDidFinishLaunching:(NSNotification *)aNotification
 {
     self.outlineView.delegate = self;
+    self.outlineView.dataSource = self;
     self.outlineView.floatsGroupRows = NO; // Prevent a sticky header
     [self addData];
 
      // Expand the first group and select the first item in the list
     [self.outlineView expandItem:[self.outlineView itemAtRow:0]];
     [self.outlineView selectRowIndexes:[NSIndexSet indexSetWithIndex:1] byExtendingSelection:NO];
+
+    // Enable Drag and Drop
+    [self.outlineView registerForDraggedTypes: [NSArray arrayWithObject: @"public.text"]];
 }
 
 
@@ -88,4 +92,61 @@ - (BOOL)outlineView:(NSOutlineView *)outlineView isGroupItem:(id)item{
     return [self isHeader:item];
 }
 
+
+#pragma mark - Drag & Drop
+
+- (id <NSPasteboardWriting>)outlineView:(NSOutlineView *)outlineView pasteboardWriterForItem:(id)item{
+    // No dragging if <some condition isn't met>
+    BOOL dragAllowed = YES;
+    if (!dragAllowed)  {
+        return nil;
+    }
+
+    Book *book = (Book *)(((NSTreeNode *)item).representedObject);
+    NSString *identifier = book.title;
+
+    NSPasteboardItem *pboardItem = [[NSPasteboardItem alloc] init];
+    [pboardItem setString:identifier forType: @"public.text"];
+
+    return pboardItem;
+}
+
+
+- (NSDragOperation)outlineView:(NSOutlineView *)outlineView validateDrop:(id < NSDraggingInfo >)info proposedItem:(id)targetItem proposedChildIndex:(NSInteger)index{
+
+    BOOL canDrag = index >= 0 && targetItem;
+
+    if (canDrag) {
+        return NSDragOperationMove;
+    }else {
+        return NSDragOperationNone;
+    }
+}
+
+
+- (BOOL)outlineView:(NSOutlineView *)outlineView acceptDrop:(id < NSDraggingInfo >)info item:(id)targetItem childIndex:(NSInteger)index{
+
+    NSPasteboard *p = [info draggingPasteboard];
+    NSString *title = [p stringForType:@"public.text"];
+    NSTreeNode *sourceNode;
+
+    for(NSTreeNode *b in [targetItem childNodes]){
+        if ([[[b representedObject] title] isEqualToString:title]){
+            sourceNode = b;
+        }
+    }
+
+    if(!sourceNode){
+        // Not found
+        return NO;
+    }
+
+    NSUInteger indexArr[] = {0,index};
+    NSIndexPath *toIndexPATH =[NSIndexPath indexPathWithIndexes:indexArr length:2];
+
+    [self.booksController moveNode:sourceNode toIndexPath:toIndexPATH];
+
+    return YES;
+}
+
 @end