Cannot debug my quicklook plugin under Xcode

Question

I'm writing a Quicklook plugin to preview App bundles. When I try to debug it under Xcode 6.1 (on Yosemite), I cannot get it to work. 'Quicklookd' launches and stays open in the dock but it doesn't render any preview and I get this output in the console:

Testing Quick Look preview with files:
    /Applications/Font Book.app
[DEBUG] Preview test for file:///Applications/Font%20Book.app/. Content type UTI: com.apple.application-bundle
[DEBUG] Previewing file:///Applications/Font%20Book.app. Content type UTI: com.apple.application-bundle. Generator used: <QLGenerator /Users/imac/Library/QuickLook/TestPlugin.qlgenerator>
[DEBUG] Loading <QLGenerator /Users/imac/Library/QuickLook/TestPlugin.qlgenerator>
[DEBUG] Previewing file:///Applications/Font%20Book.app finished
2015-02-04 10:59:35.188 qlmanage[1664:138646] *** CFMessagePort: bootstrap_register(): failed 1100 (0x44c) 'Permission denied', port = 0x9103, name = 'com.apple.CFPasteboardClient'
See /usr/include/servers/bootstrap_defs.h for the error codes.
2015-02-04 10:59:35.188 qlmanage[1664:138646] Failed to allocate communication port for com.apple.CFPasteboardClient; this is likely due to sandbox restrictions
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const: conn 0x23823 token 0x1ffffffffffe85
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: Backtrace (at 6350.6):
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  0   CoreGraphics                        0x00007fff894a9588 CGSBacktraceCreate + 112
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  1   CoreGraphics                        0x00007fff894c7940 _ZN16CGSUpdateManager14disable_updateEv + 86
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  2   AppKit                              0x00007fff90f0aa25 -[NSWindow disableScreenUpdatesUntilFlush] + 127
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  3   AppKit                              0x00007fff91442e75 -[NSVisualEffectView _createOrUpdateBackdrop:view:vibrancyEffect:] + 823
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  4   AppKit                              0x00007fff91443b92 -[NSVisualEffectView _updateCGSWindowBackdrop] + 70
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  5   AppKit                              0x00007fff91447874 -[NSVisualEffectView _update] + 147
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  6   AppKit                              0x00007fff914475a1 -[NSVisualEffectView layout] + 59
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  7   AppKit                              0x00007fff90eeca64 -[NSView _layoutSubtreeWithOldSize:] + 373
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  8   AppKit                              0x00007fff90eeccb5 -[NSView _layoutSubtreeWithOldSize:] + 966
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  9   AppKit                              0x00007fff90ee04a0 -[NSView layoutSubtreeIfNeeded] + 885
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  10  AppKit                              0x00007fff9155ff0a _NSViewLayoutSubtreesThatUseAutolayoutIfNeeded + 71
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  11  AppKit                              0x00007fff90f4181f -[NSWindow(NSConstraintBasedLayout) _layoutViewTree] + 82
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  12  AppKit                              0x00007fff90f711b9 -[NSWindow(NSConstraintBasedLayout) layoutIfNeeded] + 244
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  13  AppKit                              0x00007fff90fad1de _handleWindowNeedsDisplayOrLayoutOrUpdateConstraints + 612
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  14  AppKit                              0x00007fff915760e1 __83-[NSWindow _postWindowNeedsDisplayOrLayoutOrUpdateConstraintsUnlessPostingDisabled]_block_invoke1531 + 46
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  15  CoreFoundation                      0x00007fff8b97bda7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  16  CoreFoundation                      0x00007fff8b97bd00 __CFRunLoopDoObservers + 368
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  17  CoreFoundation                      0x00007fff8b96de08 __CFRunLoopRun + 872
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  18  CoreFoundation                      0x00007fff8b96d858 CFRunLoopRunSpecific + 296
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  19  QuickLookUI                         0x00007fff93acb8d2 -[QLPreviewView _startTimeOut] + 189
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  20  QuickLookUI                         0x00007fff93aae35e -[QLPreviewPanelController _setCurrentPreviewItem:withTransition:blocking:] + 289
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  21  QuickLookUI                         0x00007fff93aada93 -[QLPreviewPanelController _refreshLayoutAndContentBlocking:] + 250
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  22  QuickLookUI                         0x00007fff93aaf139 -[QLPreviewPanelController willOpen] + 734
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  23  QuickLookUI                         0x00007fff93aa5d04 -[QLPreviewPanel _openWithEffect:willOpen:toFullscreen:] + 897
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  24  qlmanage                            0x0000000107b11e46 qlmanage + 155206
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  25  qlmanage                            0x0000000107af14af qlmanage + 21679
Feb  4 10:59:50 iMac.local qlmanage[1664] <Warning>: void CGSUpdateManager::log() const:  26  libdyld.dylib                       0x00007fff875985c9 start + 1

However, If I test it via Finder (pressing the spacebar) it works fine displaying the preview. The problem is i cannot debug it and don't get any logs. I'm using QLPreviewRequestSetDataRepresentation with 'kUTTypeHTML' content type UTI.

How can I solve this? It used to work fine on older versions of Xcode and OS X. I need to be able to debug my plugin from Xcode. Thanks.

Answer 1

I think it's pretty clear that it's a bug in qlmanage (which is still present in 10.10.3 betas) — it doesn't show HTML output properly.

You can use two workarounds:

1. Use the qlmanage -t (or -t -s someBiggerNumber), if your code for generating thumbnails uses QLThumbnailRequestSetThumbnailWithDataRepresentation and is substantially similar to the one for previews.

2. Use qlmanage -o dir to output generated HTML to a file that you can inspect with Quicklook from Finder.