iOS开发学习-放大长图与屏幕等宽

 /* 需要得到一个图片的放大比例，这个比例就是屏幕的宽度与图片真实宽度的比值 */
 CGFloat newZoomScale = LZ_SCREEN_WIDTH / [_photoImageView.image size].width;
 CGFloat xsize = self.bounds.size.width / newZoomScale;
 CGFloat ysize = self.bounds.size.height / newZoomScale;
 [self zoomToRect:CGRectMake(- xsize/, - ysize/, xsize, ysize) animated:YES];