#import "UIImage+Alpha.h"

// Private helper methods
@interface UIImage ()
- (CGImageRef)newBorderMask:(NSUInteger)borderSize size:(CGSize)size;
@end

@implementation UIImage (Alpha)

我有错误：
什么原因是Category正在实现一个也将由其主类实现的方法？

我在整个文件中搜索newBorderMask,该单词只显示3次.

这只是宣布一次

@interface UIImage ()
- (CGImageRef)newBorderMask:(NSUInteger)borderSize size:(CGSize)size;
@end

执行一次即可

#pragma mark -
#pragma mark Private helper methods

// Creates a mask that makes the outer edges transparent and everything else opaque
// The size must include the entire mask (opaque part + transparent border)
// The caller is responsible for releasing the returned reference by calling CGImageRelease
- (CGImageRef)newBorderMask:(NSUInteger)borderSize size:(CGSize)size1 {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

并呼吁一次

CGImageRef maskImageRef = [self newBorderMask:borderSize size:newRect.size];

所以没有双重的声明.

所以有什么问题.