向 drawRect 中的 NSString 文本添加阴影:不使用 UILabel 的方法 [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阴影:

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，没有阴影选项.

是的，可以在这里使用 UILabel 并设置投影属性，但这不会那么高效，因为任何 UIView 子类(例如 UILabel)都包装了一个 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).

这是上下文:

我正在为 UITableViewCell 子类进行自定义绘图，在表格单元格视图上实现 drawRect: 而不是从复合 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.

组合一堆 UIView 子类将无法保持这种精简并在表格视图滚动性能上保持在每秒 50-60 帧之内.

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.

我曾尝试以轻微的偏移量绘制字符串两次.一旦我在我要去的单元格的背景颜色上调整阴影颜色，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，他们要么推荐使用 UILabel(我已经在上面驳回了，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中)或 CGContextSetShadow().后者似乎总是在矩形的上下文中被建议，而不一定用于将阴影附加到使用上面提到的 NSString drawAtPoint... 方法直接绘制的文本路径.(我确实尝试过，但似乎没有用(即没有任何变化)；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

CGContextSetShadow() 对我来说效果很好.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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