Objective- C:在UIImage上绘制边框

// 假设你有一个UIImage对象叫做originalImage
UIImage *originalImage = [UIImage imageNamed:@"your_image_name"];

// 边框宽度
CGFloat borderWidth = 5.0;

// 创建一个新的图形上下文，大小为原始图像加上两倍的边框宽度
UIGraphicsBeginImageContextWithOptions(CGSizeMake(originalImage.size.width + 2 * borderWidth, originalImage.size.height + 2 * borderWidth), NO, 0.0);

// 获取当前图形上下文的上下文
CGContextRef context = UIGraphicsGetCurrentContext();

// 绘制边框
[[UIColor blackColor] setStroke];
CGContextSetLineWidth(context, borderWidth);
CGContextStrokeRect(context, CGRectMake(borderWidth / 2, borderWidth / 2, originalImage.size.width, originalImage.size.height));

// 绘制原始图像
[originalImage drawInRect:CGRectMake(borderWidth, borderWidth, originalImage.size.width, originalImage.size.height)];

// 从当前图形上下文中获取新的带边框的UIImage
UIImage *borderedImage = UIGraphicsGetImageFromCurrentImageContext();

// 结束图形上下文
UIGraphicsEndImageContext();

// 现在你有了一个带边框的UIImage对象borderedImage