UIView setNeedsDisplay是否没有效果？

Question

I have a UIView-derived view that is drawn only once and never updated .

Calling [self setNeedsDisplay] has no effect. What could cause this?

It doesn't matter whether the drawing code is in

• drawRect: , or
• drawLayer:inContext: (with an empty drawRect() defined)

If drawLayer:inContext is not defined, then drawRect is called. But just once (during layout).

- (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)ctx {
  // drawing occurs, but just once (during view layout)
}

`- (void)drawRect:(CGRect) rect {
  // empty -- never called
}

A small list of what I've tried:

• [self setNeedsDisplay]
• [self.layer setNeedsDisplay]
• [self.mySubLayer setNeedsDisplay]
• self.contentMode = UIViewContentModeRedraw;
• creating the view manually, instead of loading it from a .nib (no effect)
• Removing the use of layers (and sublayers) and using just drawRect (no effect)

Answer 1

因此，可以将其标记为已回答：确保在主线程上调用UIKit方法。