Question

我有一个带有UIImage的UITableViewCell，我正在绘制。当我滚动时，我得到了大量的子层，这使得性能真的很不稳定。如何确保我的CALayer只添加一次？

- (void) drawContentView:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIColor whiteColor] set];
    CGContextFillRect(context, rect);

    NSString* caption = [NSString stringWithFormat:@"%@",[info objectForKey:@"caption"]];
    NSString* text = [info stringForKey:@"text"];

    CGFloat widthr = self.frame.size.width - 70;

    [[UIColor grayColor] set];
    [text drawInRect:CGRectMake(63.0, 25.0, widthr, 20.0) withFont:system14 lineBreakMode:UILineBreakModeTailTruncation];

    if (self.image) {
        UIImage *imageToDisplay;
        imageToDisplay = self.image;
        imageToDisplay = [self imageWithImage:imageToDisplay scaledToSize:CGSizeMake(imageToDisplay.size.width / 1.5, imageToDisplay.size.height / 1.5)];
        CGFloat width;
        CGFloat height;
        CGRect r;
        if (imageToDisplay.size.width < 310 && imageToDisplay.size.height > 290) {
            imageToDisplay = [self imageByCropping:imageToDisplay toRect:CGRectMake(0, 20, imageToDisplay.size.width, 270)];

        }
        else if (imageToDisplay.size.width > 310 && imageToDisplay.size.height < 20) {
            imageToDisplay = [self imageByCropping:imageToDisplay toRect:CGRectMake(30, 0, 290, imageToDisplay.size.height)];
        }
        else {
            if (![caption isEqualToString:@""]) {
                imageToDisplay = [self imageByCropping:imageToDisplay toRect:CGRectMake(30, 0, 290, 230)];
            }
            else {
            imageToDisplay = [self imageByCropping:imageToDisplay toRect:CGRectMake(30, 0, 290, 270)];
            }
        }

        width = imageToDisplay.size.width;
        height = imageToDisplay.size.height;
        r = CGRectMake(5.0, 5.0, width, height);

        //[imageToDisplay drawInRect:r];

        CALayer *sublayer = [CALayer layer];
        sublayer.contents = (id)imageToDisplay.CGImage;
        sublayer.shadowOffset = CGSizeMake(0, 3);
        sublayer.shadowRadius = 5.0;
        sublayer.shadowColor = [UIColor blackColor].CGColor;
        sublayer.shadowOpacity = 0.8;
        sublayer.frame = CGRectMake(5.0, 5.0, imageToDisplay.size.width, imageToDisplay.size.height);
        [self.layer addSublayer:sublayer];

        //Experimental shadow stuff with images
        /*CALayer *layer = [CALayer layer];
        layer = [CALayer layer];
        layer.bounds = CGRectMake(5.0, 5.0, imageToDisplay.size.width, imageToDisplay.size.height);
        layer.position = CGPointMake(150, 140);
        layer.contents = (id)imageToDisplay.CGImage;    

        layer.shadowOffset = CGSizeMake(0, 2);
        layer.shadowOpacity = 0.70;

        [self.layer addSublayer:layer];

        [self bezierPathWithCurvedShadowForRect:layer.bounds];*/

        [[UIColor blackColor] set];
        [caption drawInRect:CGRectMake(10.0, height + 20 , widthr, 20.0) withFont:system14 lineBreakMode:UILineBreakModeWordWrap alignment:UITextAlignmentCenter];
    }
}

Answer 1

drawContentView:不是调用addSublayer:的正确方法。您应该在使用image构造对象时，或者在现有对象上设置image时添加该图层。或者，您可以在drawContentView:中自己绘制图像，但可能不会那么快。

滚动我的UITableView时，为什么CALayers会叠加在一起？

1 个答案: