我有一个UIView的子类,我有一个drawRect实现。我基本上想要在设置CGPoint后调用这个drawRect,这是这个UIView的一个属性。我该怎么做呢?这里是我的代码:在UIView子类中调用drawRect
-(id) initWithCoder:(NSCoder *)aDecoder
{
if(self = [super initWithCoder:aDecoder]) {
point_.x = 0;
self.page_ = [UIImage imageNamed:@"pages"];
}
return self;
}
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
if (point_.x != 0){
[self.page_ drawInRect:rect];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);
CGContextSetLineWidth(context, 1.0f);
CGContextMoveToPoint(context, 40, point_.y);
CGContextAddLineToPoint(context, 420, point_.y);
CGContextStrokePath(context);
}
}
当我设置这个UIView的点和我打电话的drawRect我在其他的UIViewController喜欢如下:
self.page_.point_ = CGPointMake(-100, self.title_.frameHeight + self.title_.frameX + 40);
[self.page_ drawRect:self.page_.frame];
它给了我所有的这些错误:
<Error>: CGContextSaveGState: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextSetBlendMode: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextSetAlpha: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextTranslateCTM: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextScaleCTM: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextDrawImage: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextRestoreGState: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextSetStrokeColorWithColor: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextSetLineWidth: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextMoveToPoint: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextAddLineToPoint: invalid context 0x0
Feb 22 20:24:38 <Error>: CGContextDrawPath: invalid context 0x0
这是为什么?
如果'point_'的值实际发生了变化,那么'point_'属性setter调用'setNeedsDisplay'会更好。 – 2012-02-23 04:46:42
aha ..这是一个好主意..所以在我的setteer中我会打电话给setNeedsDisplay。介意解释为什么这样更好? – adit 2012-02-23 05:07:04