iphone - 为什么程序背景会减慢 UIScrollView？

Question

我的问题代码位于程序背景中，我在 UIView (drawRect:) 中进行绘制，然后将其作为子视图添加到 UIScrollView。程序代码如下。它绘制盒子形状，看起来有点像天际线。任何想法为什么这会减慢我的 UIScrollView？它似乎只在第一个滚动时很慢，然后就好像它被缓存了一样。背景有时可能高达一千像素宽或更多。看图...

- (void)drawRect:(CGRect)rect
{
UIBezierPath *vertLine = [[UIBezierPath alloc] init];

[vertLine moveToPoint:CGPointMake(0,self.frame.size.height)];

int detail = 10;
int ranNum = 0;
int count = self.bounds.size.width/detail;
CGFloat heightIncrement = 0.0;

CGFloat minHeight = self.frame.size.height;

CGFloat xPos = 0;
CGFloat yPos = self.frame.size.height-20;

for (int i =0; i<count; i++)
{
    ranNum += (arc4random() % 9)-5;

    yPos -= (arc4random() % 30);
    [vertLine addLineToPoint:CGPointMake(xPos,yPos)];

    xPos += (arc4random() % 20)+10;
    [vertLine addLineToPoint:CGPointMake(xPos,yPos)];

    yPos += (arc4random() % 30);
    [vertLine addLineToPoint:CGPointMake(xPos,yPos)];

    xPos += (arc4random() % 30);
    [vertLine addLineToPoint:CGPointMake(xPos,yPos)];

    if (yPos>self.frame.size.height-10) {
        yPos = self.frame.size.height-10;
    }

    if (yPos<self.frame.size.height-50) {
        yPos = self.frame.size.height-50;
    }

}

[vertLine addLineToPoint:CGPointMake(count*20,(self.frame.size.height))];

[[UIColor colorWithRed:0.0/255.0 green:38.0/255.0 blue:51.0/255 alpha:1] setFill];

[vertLine fill];

}

Answer 1

可能是因为您超出了滚动范围。尝试：

[yourScrollView setContentOffest:CGPointMake(0,0)];