Question

我已经将UIView子类化，并且我实现了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：

-(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的点，我在我的其他UIViewController中调用drawRect，如下所示：

 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：

  <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？

Answer 1

您永远不应该直接致电-drawRect:。

改为使用-setNeedsDisplay：

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（又称CGRect将传递给-drawRect:），您可以使用-setNeedsDisplayInRect:

正如@rob mayoff建议的那样，您可以覆盖point_属性的setter：

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

Answer 2

- (id)initWithCoder:(NSCoder *)aDecoder // (1)
{
if (self = [super initWithCoder:aDecoder])
{
    [self setMultipleTouchEnabled:NO]; // (2)
    [self setBackgroundColor:[UIColor whiteColor]];
    path = [UIBezierPath bezierPath];
    [path setLineWidth:2.0]; 
}
return self;
}


- (void) drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(context, 0.0, 0.0, 0.0, 1.0);
CGContextSetLineWidth(context, 3.0);
CGContextDrawPath(context, kCGPathFillStroke);    //CGContextSetRGBFillColor doesn't work either
CGContextBeginPath(context);
CGContextMoveToPoint(context, 100.0, 60.0);
CGRect rectangle = {100.0, 60.0, 120.0, 120.0};
CGContextAddRect(context, rectangle);

CGContextStrokePath(context);
CGContextFillPath(context);
}
this code implement in create new uiview and add this code i hope that code you usefull.

Answer 3

将您的绘图代码包装进去 UIGraphicsPushContext( context ) 和UIGraphicsPopContext()以避免此错误消息。

在UIView子类中调用drawRect

3 个答案: