added MPCollectionView to track index for context menu

MacPass/MPCollectionView.m

@@ -0,0 +1,44 @@
+//
+//  MPCollectionView.m
+//  MacPass
+//
+//  Created by Michael Starke on 18.09.17.
+//  Copyright © 2017 HicknHack Software GmbH. All rights reserved.
+//
+
+#import "MPCollectionView.h"
+
+@implementation MPCollectionView
+
+- (instancetype)initWithCoder:(NSCoder *)coder {
+  self = [super initWithCoder:coder];
+  if(self) {
+    _contextMenuIndex = NSNotFound;
+  }
+  return self;
+}
+
+- (instancetype)initWithFrame:(NSRect)frameRect {
+  self = [super initWithFrame:frameRect];
+  if(self) {
+    _contextMenuIndex = NSNotFound;
+  }
+  return self;
+}
+
+- (NSMenu *)menuForEvent:(NSEvent *)event {
+  self.contextMenuIndex = NSNotFound;
+  NSPoint point = [self convertPoint:event.locationInWindow fromView:nil];
+  NSUInteger count = self.content.count;
+  for (NSUInteger i = 0; i < count; i++) {
+    NSRect itemFrame = [self frameForItemAtIndex:i];
+    if (NSMouseInRect(point, itemFrame, self.isFlipped)) {
+      self.contextMenuIndex = i;
+      break;
+    }
+  }
+  
+  return [super menuForEvent:event];
+}
+
+@end