怎么拿到一张Image的主色调呢？怎样避免imageWithNa

继续给UIImage加扩展吧、

• 主色调读取

- (UIColor *)averageColor {
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char rgba[4];
    CGContextRef context = CGBitmapContextCreate(rgba, 1, 1, 8, 4, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    
    CGContextDrawImage(context, CGRectMake(0, 0, 1, 1), self.CGImage);
    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);
    
    if(rgba[3] == 0) {
        CGFloat alpha = ((CGFloat)rgba[3])/255.0;
        CGFloat multiplier = alpha/255.0;
        return [UIColor colorWithRed:((CGFloat)rgba[0])*multiplier
                               green:((CGFloat)rgba[1])*multiplier
                                blue:((CGFloat)rgba[2])*multiplier
                               alpha:alpha];
    }
    else {
        return [UIColor colorWithRed:((CGFloat)rgba[0])/255.0
                               green:((CGFloat)rgba[1])/255.0
                                blue:((CGFloat)rgba[2])/255.0
                               alpha:((CGFloat)rgba[3])/255.0];
    }
}

• UIImage读取

+ (UIImage *)imageWithFileName:(NSString *)name {
    NSString *extension = @"png";
    
    NSArray *components = [name componentsSeparatedByString:@"."];
    if ([components count] >= 2) {
        NSUInteger lastIndex = components.count - 1;
        extension = [components objectAtIndex:lastIndex];
        
        name = [name substringToIndex:(name.length-(extension.length+1))];
    }
    
    // 如果为Retina屏幕且存在对应图片，则返回Retina图片，否则查找普通图片
    if ([UIScreen mainScreen].scale == 2.0) {
        name = [name stringByAppendingString:@"@2x"];
        
        NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:extension];
        if (path != nil) {
            return [UIImage imageWithContentsOfFile:path];
        }
    }
    
    if ([UIScreen mainScreen].scale == 3.0) {
        name = [name stringByAppendingString:@"@3x"];
        
        NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:extension];
        if (path != nil) {
            return [UIImage imageWithContentsOfFile:path];
        }
    }
    
    NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:extension];
    if (path) {
        return [UIImage imageWithContentsOfFile:path];
    }
    
    return nil;
}

• 水印, 文字以及图片

- (UIImage*)imageWaterMarkWithString:(NSString*)str rect:(CGRect)strRect attribute:(NSDictionary *)attri image:(UIImage *)image imageRect:(CGRect)imgRect alpha:(CGFloat)alpha {
    
    UIGraphicsBeginImageContext(self.size);
    [self drawInRect:CGRectMake(0, 0, self.size.width, self.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
    if (image) {
        [image drawInRect:imgRect blendMode:kCGBlendModeNormal alpha:alpha];
    }
    
    if (str) {
        [str drawInRect:strRect withAttributes:attri];
    }
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resultImage;
}