解决方法
我在GitHub上找到了一个函数,它对我来说很好.
func resize(image: NSImage,w: Int,h: Int) -> NSImage {
var destSize = NSMakeSize(CGFloat(w),CGFloat(h))
var newImage = NSImage(size: destSize)
newImage.lockFocus()
image.drawInRect(NSMakeRect(0,destSize.width,destSize.height),fromRect: NSMakeRect(0,image.size.width,image.size.height),operation: NSCompositingOperation.CompositeSourceOver,fraction: CGFloat(1))
newImage.unlockFocus()
newImage.size = destSize
return NSImage(data: newImage.TIFFRepresentation!)!
}