在不使用UILabel的情况下，在drawRect：方法中为NSString文本添加投影 [英] Adding a drop shadow to NSString text in a drawRect: method without using UILabel
问题描述
我想为使用iOS提供的 NSString（UIStringDrawing）类别方法绘制的文本添加投影：
I'd like to add a drop shadow to text drawn using the iOS supplied NSString (UIStringDrawing) category method:
- (CGSize)drawAtPoint:(CGPoint)point forWidth:(CGFloat)width
withFont:(UIFont *)font minFontSize:(CGFloat)minFontSize
actualFontSize:(CGFloat *)actualFontSize
lineBreakMode:(UILineBreakMode)lineBreakMode
baselineAdjustment:(UIBaselineAdjustment)baselineAdjustment;
显然，没有投影选项。
Clearly, there's no drop shadow option.
是的，可以在这里使用UILabel并获得设置的阴影属性，但这不会有效果，因为任何UIView子类（如UILabel）都会包含一个CALayer对象并且会更重（性能明智）。
Yes, one could use a UILabel here and get drop shadow properties to set, but that wouldn't be as performant, since any UIView subclass (such as UILabel) wraps a CALayer object and is going to be heavier (performance wise).
以下是上下文：
我'为UITableViewCell子类做自定义绘图，在表格单元视图上实现 drawRect：，而不是从合成的UIView子类的Nib文件创建表格单元格。
I'm doing custom drawing for a UITableViewCell subclass, implementing drawRect: on the table cell view instead of creating the table cell from a Nib file of composited UIView subclasses.
合成一堆UIView子类会破坏尝试保持这种精益的目的，并在表格视图滚动性能中保持在每秒50-60帧内。
Compositing a bunch of UIView subclasses would defeat the purpose of trying to keep this lean and stay within 50-60 frames per second in table view scrolling performance.
我尝试过轻微偏移两次绘制字符串。一旦我调整了我已经去过的单元格的背景颜色上的投影颜色，这可能会变得可以接受，但它似乎相当笨拙。当然没有像UILabel那样的阴影模糊属性。
I have tried drawing the string twice at a slight offset. This may turn out acceptable once I tweak the drop shadow color on the background color of the cell that I have going, but it seems rather kludgey. Certainly there's no drop shadow blur property like one gets with UILabel.
我搜索了解决方案并且他们要么推荐使用UILabel（我已经解雇过了，因为我有大约十几个不同的文本元素被合成到表格单元格视图上）或 CGContextSetShadow（）。后者似乎总是在矩形形状的上下文中建议，并不一定用于将阴影附加到直接使用NSString drawAtPoint ... 方法绘制的文本路径以上。 （我确实尝试过，但它似乎没有用（即没有改变）;我是Core Graphics绘图的新手。）
I searched for solutions and they either recommend UILabel usage (which I've dismissed per above, since I have about a dozen distinct textual elements getting composited on to the table cell view) or CGContextSetShadow(). The latter always seems to be suggested in the context of rectangular shapes, and not necessarily for attaching a shadow to the path of text drawn directly with the NSString drawAtPoint... method mentioned above. (I did try it, but it didn't seem to work (i.e. nothing changed); I'm new to Core Graphics drawing).
建议？
推荐答案
使用 CGContextSetShadow（）对我来说很好。示例：
It works fine for me with CGContextSetShadow(). Example:
- (void)drawRect:(CGRect)rect
{
NSString *string = @"Hello World!";
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetShadow(context, CGSizeMake(20.0f, 20.0f), 10.0f);
[string drawAtPoint:CGPointMake(100.0f, 100.0f) withFont:[UIFont boldSystemFontOfSize:36.0f]];
}
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