添加“被盗”商品是否安全？ UILabel的层到其他CALayer的子层？ [英] Is it safe to add a "stolen" UILabel's layer to some other CALayer's sublayer?

问题描述

我阅读了

I read this and this but they don't seem to address the issue. And the answers to this seem to go off a tangent in NSCoding and friends, so ...

Consider:

- (NSAttributedString *) attributedStringForText: (NSString *) text {
    NSMutableAttributedString* attrStr = [[NSMutableAttributedString alloc] initWithString:text];
    UIFont * bigF = [UIFont fontWithName:@"OpenSans-Extrabold" size:20.0f] ;
    UIFont * smaF = [UIFont fontWithName:@"OpenSans-Extrabold" size:12.0f] ;

    [attrStr addAttribute:NSFontAttributeName value:bigF range:(NSRange){0, 3}] ;
    [attrStr addAttribute:NSFontAttributeName value:smaF range:(NSRange){3, 6}] ;
    [attrStr addAttribute:NSFontAttributeName value:bigF range:(NSRange){6, [text length]-6}] ;

    [attrStr addAttribute:NSBackgroundColorAttributeName value:[UIColor brownColor] range:(NSRange){3, 6}] ;
    return attrStr ;
}

- (CALayer *) stealLayerFromUILabelForText: (NSString *) text inRect: (CGRect) bounds {
    UILabel * label = [[UILabel alloc] initWithFrame:bounds] ;
    label.textColor = [UIColor whiteColor] ;
    label.font = [UIFont fontWithName:@"OpenSans-Extrabold" size:20.0f] ;
    label.attributedText = [self attributedStringForText:text] ;
    [label sizeToFit] ;
    [label.layer display] ; // Yup!
    return label.layer ;
}

and

- (void) setupLayer: (CALayer *) tileLayer
               text: (NSString *) text
              index: (NSUInteger) index {

    CGRect (^center_rect)(CGRect, CGRect) = ^CGRect (CGRect r, CGRect into) {
        CGRect centered = into ;
        centered.origin.x += (into.size.width - r.size.width) / 2.0f ;
        centered.origin.y += (into.size.height - r.size.height) / 2.0f ;
        centered.size = r.size ;
        return centered ;
    } ;

    CALayer * layer = [self stealLayerFromUILabelForText:text inRect:tileLayer.bounds] ;
    CGRect frame = center_rect(layer.bounds, tileLayer.bounds) ;

    [tileLayer addSublayer:layer] ;

    layer.frame = frame ;
}

This works:

But I am concerned that I am somehow abusing UILabel & CALayer. On one hand UIView, UILabel and all are just a thin touch aware veneer on top of the real CALayer hierarchy. OTOH I am somehow relying on probably many not even stated assumptions here.

Anyone sees why this would break further down the road, or, better, can prove that it won't?

解决方案

I've used this technique since 2013 and it's still stable. So yes, I think this is safe for now. Previously I was doing this without calling -display on iOS 4 or 5, which no longer works when compiled against newer SDKs, so thanks for this tidbit.

There is more information here if you're looking for other options: Add text to CALayer

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