How to add a secondary window to a document-based app - objective-c

Question

I want to add a secondary window containing resources that can be dragged and dropped into NSDocuments.
My project contains:
1) ResourceWindow.xib
2) ViewController.xib
3) Main.storyboard
#interface AppDelegate ()
#property (nonatomic,strong)NSWindowController* wc;
#property (nonatomic, weak)NSWindow* resourceWindow;
#property (nonatomic, strong)ViewController* vc;
#end
#implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
self.wc = [[NSWindowController alloc]initWithWindowNibName:#"ResourceController.xib"];
self.resourceWindow = [self.wc window];
[self.wc showWindow:self];
self.vc = [[ViewController alloc]initWithNibName:nil bundle:nil];
[self.vc.view setFrame:[self.resourceWindow.contentView bounds]];
[self.resourceWindow.contentView addSubview:self.vc.view];
}
self.wc.window is nil immediately after allocating and initializing it.
Please set me straight on this.
Thanks
EDIT:
ResourceWindow.xib does not contain a window controller just a window . Is that the problem? Is the solution to drag and drop a custom object into the xib file and change it's class to NSWindowController?

Answer 1

In addition to the file name issue pointed to by Willeke, windows are nil until showWindow is called. Sigh. I started again by subclassing NSWindowManager and checking add xib file. Then, set the class of files owner to SourceWindowController and changed the code to:
#property (nonatomic,strong)SourceWindowController* wc;
#property (nonatomic, weak)NSWindow* resourceWindow;
#end
#implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
self.wc = [[SourceWindowController alloc]initWithWindowNibName:#"SourceWindowController"];
[self.wc showWindow:self.window];
self.resourceWindow = [self.wc window];