Does UIView's -drawRect: have to be called on the main thread?

Question

Does UIView's -drawRect: method have to be drawn on the main thread or can CADisplayLink call -setNeedsDisplay on a custom view in a different run loop?

score 10 · Answer 1 · answered Dec 16 '11 at 20:29

As of iOS 4.0, you can draw within a UIView's -drawRect: on a background thread:

Drawing to a graphics context in UIKit is now thread-safe. Specifically:

The routines used to access and manipulate the graphics context can now correctly handle contexts residing on different threads.

String and image drawing is now thread-safe.

Using color and font objects in multiple threads is now safe to do.

See also their comments in Technical Q&A QA1637 regarding this in iOS 4.0.

Any version of iOS before that still needs to have this drawing be on the main thread.

score 2 · Accepted Answer · answered Mar 03 '11 at 15:23

2

All UIKit calls should be done on the main thread.

answered Mar 03 '11 at 15:23

Jeff Kelley

19,021
6
70
80

2

As I explain in my answer, as of iOS 4.0 you can indeed draw to a UIView within a background thread. – Brad Larson Dec 16 '11 at 20:29

Does UIView's -drawRect: have to be called on the main thread?

2 Answers2

Linked