@interface YYLabel : UIView
@property NSString *text;
@property UIFont *font;
@end

@implementation YYLabel


- (void)setText:(NSString *)text {

    _text = text.copy;

    [[YYTransaction transactionWithTarget:self selector:@selector(contentsNeedUpdated)] commit];

}


- (void)setFont:(UIFont *)font {

    _font = font;

    [[YYTransaction transactionWithTarget:self selector:@selector(contentsNeedUpdated)] commit];

}


- (void)layoutSubviews {

    [super layoutSubviews];

    [[YYTransaction transactionWithTarget:self selector:@selector(contentsNeedUpdated)] commit];

}


- (void)contentsNeedUpdated {
// do update

    [self.layer setNeedsDisplay];

}


#pragma mark - YYAsyncLayer


+ (Class)layerClass {
return YYAsyncLayer.class;

}


- (YYAsyncLayerDisplayTask *)newAsyncDisplayTask {

// capture current state to display task
NSString *text = _text;

    UIFont *font = _font;


    YYAsyncLayerDisplayTask *task = [YYAsyncLayerDisplayTask new];

    task.willDisplay = ^(CALayer *layer) {
//...

    };


    task.display = ^(CGContextRef context, CGSize size, BOOL(^isCancelled)(void)) {
if (isCancelled()) return;
NSArray *lines = CreateCTLines(text, font, size.width);
if (isCancelled()) return;

for (int i = 0; i < lines.count; i++) {

            CTLineRef line = line[i];
CGContextSetTextPosition(context, 0, i * font.pointSize * 1.5);
CTLineDraw(line, context);
if (isCancelled()) return;

        }

    };


    task.didDisplay = ^(CALayer *layer, BOOL finished) {
if (finished) {
// finished

        } else {
// cancelled

        }

    };

return task;

}
@end