title: DTCoreText got a warning of " UI API called on a background thread"
body: <p>seems the latest code of DTCoreText in the Github still didn't fix this . how to fix this warning well?
  <a href="https://i.stack.imgur.com/Q3mU4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Q3mU4.png" alt="enter image description here"></a></p>
  
  <p>and the stacktrace is as this</p>
  
  <pre><code>PID: 80642, TID: 3065451, Thread name: (none), Queue name: com.apple.root.default-qos, QoS: 21
  Backtrace:
  4   iKM                                 0x00000001031a2232 -[DTAttributedTextContentView drawLayer:inContext:] + 210
  5   QuartzCore                          0x000000010766502c -[CALayer drawInContext:] + 267
  6   QuartzCore                          0x00000001075b1042 _ZL18tiled_layer_renderP16_CAImageProviderjjjjPv + 1817
  7   QuartzCore                          0x000000010763b4ce _ZL21CAImageProviderThreadPjb + 789
  8   libdispatch.dylib                   0x000000010cc8443c _dispatch_client_callout + 8
  9   libdispatch.dylib                   0x000000010cc89352 _dispatch_queue_override_invoke + 1458
  10  libdispatch.dylib                   0x000000010cc901f9 _dispatch_root_queue_drain + 772
  11  libdispatch.dylib                   0x000000010cc8fe97 _dispatch_worker_thread3 + 132
  12  libsystem_pthread.dylib             0x000000010d14c1ca _pthread_wqthread + 1387
  13  libsystem_pthread.dylib             0x000000010d14bc4d start_wqthread + 13
  </code></pre>