UIImage+Resize.swift

extension UIImage {
    func resize(size:CGSize) -> UIImage?{
        // リサイズ処理
        let origWidth = self.size.width
        let origHeight = self.size.height
        
        var resizeWidth:CGFloat = 0
        var resizeHeight:CGFloat = 0
        if (origWidth < origHeight) {
            resizeWidth = size.width
            resizeHeight = origHeight * resizeWidth / origWidth
        } else {
            resizeHeight = size.height
            resizeWidth = origWidth * resizeHeight / origHeight
        }
        
        let resizeSize = CGSize(width:resizeWidth, height:resizeHeight)
        UIGraphicsBeginImageContext(resizeSize)
        
        self.draw(in: CGRect(x:0,y: 0,width: resizeWidth, height: resizeHeight))
        
        let resizeImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        // 切り抜き処理
        let cropRect = CGRect(x:( resizeWidth - size.width ) / 2,
                              y:( resizeHeight - size.height) / 2,
                              width:size.width,
                              height:size.height)
        
        if let cropRef = resizeImage?.cgImage {
            cropRef.cropping(to: cropRect)
            let cropImage = UIImage(cgImage: cropRef)
            return cropImage
        }else {
            print("error!")
            return nil
        }
    }
    
    //向きがおかしくなる時用
    func resizeMaintainDirection(size:CGSize) -> UIImage?{
        
        //縦横がおかしくなる時は一度書き直すと良いらしい
        UIGraphicsBeginImageContextWithOptions(self.size, false, 0.0)
        self.draw(in:CGRect(x:0,y:0,width:self.size.width,height:self.size.height))
        guard let image = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
        UIGraphicsEndImageContext()
        
        // リサイズ処理
        let origWidth = image.size.width
        let origHeight = image.size.height
        
        var resizeWidth:CGFloat = 0
        var resizeHeight:CGFloat = 0
        if (origWidth < origHeight) {
            resizeWidth = size.width
            resizeHeight = origHeight * resizeWidth / origWidth
        } else {
            resizeHeight = size.height
            resizeWidth = origWidth * resizeHeight / origHeight
        }
        
        let resizeSize = CGSize(width:resizeWidth, height:resizeHeight)
        UIGraphicsBeginImageContext(resizeSize)
        
        image.draw(in: CGRect(x:0,y: 0,width: resizeWidth, height: resizeHeight))
        
        let resizeImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        // 切り抜き処理
        let cropRect = CGRect(x:( resizeWidth - size.width ) / 2,
                              y:( resizeHeight - size.height) / 2,
                              width:size.width,
                              height:size.height)
        
        if let cropRef = resizeImage?.cgImage {
            cropRef.cropping(to: cropRect)
            let cropImage = UIImage(cgImage: cropRef)
            return cropImage
        }else {
            print("error!")
            return nil
        }
    }
}