我正在尝试调试一个真正困扰我的问题。基本上，我有一个 UIView 子类，它根据我在 init 方法中提供的颜色在 drawRect: 中为自身绘制渐变。当视图再次绘制自身时会出现问题。如果我在视图上调用 setNeedsDisplay，或者说视图由于内存不足警告而被删除，并且稍后会重新添加（这也会再次触发 drawRect:），那么视图的背景是完全空白的。我不确定为什么重绘渐变会导致这种情况发生；有人知道可能出了什么问题吗？这是我在drawRect中的代码摘录：
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGContextSaveGState(currentContext);
int startcolorNumComponents = CGColorGetNumberOfComponents(self.topColor.CGColor);
int endcolorNumComponents = CGColorGetNumberOfComponents(self.bottomColor.CGColor);
// get the array of floats for each of the gradient colors
const CGFloat *startComponents = CGColorGetComponents(self.topColor.CGColor);
const CGFloat *endComponents = CGColorGetComponents(self.bottomColor.CGColor);
CGFloat redStart = startComponents[0];
CGFloat greenStart = (startcolorNumComponents != 2 )? startComponents[1] : startComponents[0];
CGFloat blueStart = (startcolorNumComponents != 2 )? startComponents[2] : startComponents[0];
CGFloat startAlpha = (startcolorNumComponents != 2 )? startComponents[3] : startComponents[1];
CGFloat redEnd = endComponents[0];
CGFloat greenEnd = (endcolorNumComponents != 2) ? endComponents[1] : endComponents[0];
CGFloat blueEnd = (endcolorNumComponents != 2) ? endComponents[2] : endComponents[0];
CGFloat endAlpha = (endcolorNumComponents != 2) ? endComponents[3] : endComponents[1];
CGFloat components[8] = { redStart, greenStart, blueStart, startAlpha, redEnd, greenEnd, blueEnd, endAlpha };
size_t num_locations = 2;
CGFloat locations[2] = { 0.0, 1.0 };
CGGradientRef glossGradient = CGGradientCreateWithColorComponents(CGColorSpaceCreateDeviceRGB(), components, locations, num_locations);
CGPoint gradientStart = CGPointMake(CGRectGetMidX(self.bounds), self.bounds.origin.x);
CGPoint gradientEnd = CGPointMake(CGRectGetMidX(self.bounds),self.bounds.size.height));
CGContextDrawLinearGradient(currentContext, glossGradient, gradientStart, gradientEnd, 0.0);
CGGradientRelease(glossGradient);
CGContextRestoreGState(currentContext);