在UIView子类中调用drawRect [英] calling drawRect in a UIView subclass

问题描述

我已经将UIView子类化了，并且我实现了一个drawRect。我基本上希望在设置CGPoint之后调用这个drawRect，这是这​​个UIView的属性。我该怎么做呢？这是我的代码：

I have subclassed a UIView and I have a drawRect implemented. I basically want this drawRect to be called after I've set the CGPoint, which is a property of this UIView. How do I do this? Here's my code:

-(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);
    }
}

当我设定这个UIView和我在我的其他UIViewController中调用drawRect，如下所示：

When I've set the point of this UIView and I call drawRect in my other UIViewController like follows:

 self.page_.point_ = CGPointMake(-100, self.title_.frameHeight + self.title_.frameX + 40);
    [self.page_ drawRect:self.page_.frame];

它给了我所有这些错误：

It gives me all of these errors:

  <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

为什么会这样？

推荐答案

你永远不应该打电话给 -drawRect：直接。

使用 -setNeedsDisplay 代替：

self.page_.point_ = CGPointMake(-100, self.title_.frameHeight + self.title_.frameX + 40);
[self.page_ setNeedsDisplay];

如果您需要自定义绘图区域（又名 CGRect 将传递给 -drawRect：），你可以使用 -setNeedsDisplayInRect：

If you need to customize the drawing area (aka the CGRect that will be passed to -drawRect:), you can use -setNeedsDisplayInRect:

如 @rob mayoff 所建议，您可以覆盖设置者点_ 属性：

As @rob mayoff has suggested, you can override the setter for the point_ property:

- (void)setPoint_:(CGPoint)point {
   if(!CGPointEqualToPoint(point_, point)) {
      point_ = point;
      [self setNeedsDisplay];
   }
}

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