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iOS开发之UIImage等比缩放

评论功能真不错

评论开通后，果然有很多人吐槽。谢谢大家的支持和关爱，如果有做的不到的地方，还请海涵。毕竟我一个人的力量是有限的，我会尽自己最大的努力大家准备一些干货。

有些内容可能都是比较基础的，记住：不积跬步无以至千里，不积小流无以成江海。我想这个道理大家都懂，在为大家准备文章的过程中，对我来说也是一次学习成长。

大家可以继续吐槽！微信的评论就是一个沟通的渠道，也是一篇文章的延续。你也可以在评论中写一些你对iOS开发的见解，说不定就会对他人有帮助。

很高兴，已经有好几位iOS开发的朋友答应以后会写文章投稿给我。在这里，我再强调一下：如果你有好的技术文章一定要投稿给我噢！投稿邮箱：

worldligang@163.com

前面讲了截取UIImage指定大小区域，很方便的截取 UIImage 。今天要和大家分享的是 UIImage 的缩放。

两种缩放:

缩放到指定大小，也就是指定的 size .
等比缩放。

缩放到指定大小

- (UIImage*)imageCompressWithSimple:(UIImage*)image scaledToSize:(CGSize)size {  UIGraphicsBeginImageContext(size);  [image drawInRect:CGRectMake(0,0,size.width,size.height)];  UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();  UIGraphicsEndImageContext();  return newImage; }

等比缩放

通过缩放系数

- (UIImage*)imageCompressWithSimple:(UIImage*)image scale:(float)scale {  CGSize size = image.size;  CGFloat width = size.width;  CGFloat height = size.height;  CGFloat scaledWidth = width * scale;  CGFloat scaledHeight = height * scale;  UIGraphicsBeginImageContext(size); // this will crop  [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];  UIImage* newImage= UIGraphicsGetImageFromCurrentImageContext();  UIGraphicsEndImageContext();  return newImage; }

scale 是缩放系数。

通过计算得到缩放系数

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize {  UIImage *sourceImage = [UIImage imageNamed:@"test.jpg"];  UIImage *newImage = nil;  CGSize imageSize = sourceImage.size;  CGFloat width = imageSize.width;  CGFloat height = imageSize.height;  CGFloat targetWidth = targetSize.width;  CGFloat targetHeight = targetSize.height;  CGFloat scaleFactor = 0.0;  CGFloat scaledWidth = targetWidth;  CGFloat scaledHeight = targetHeight;  CGPoint thumbnailPoint = CGPointMake(0.0,0.0);  if (CGSizeEqualToSize(imageSize, targetSize) == NO)  {   CGFloat widthFactor = targetWidth / width;   CGFloat heightFactor = targetHeight / height;   if (widthFactor > heightFactor)    scaleFactor = widthFactor; // scale to fit height   else    scaleFactor = heightFactor; // scale to fit width   scaledWidth= width * scaleFactor;   scaledHeight = height * scaleFactor;   // center the image   if (widthFactor > heightFactor)   {    thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;   }   else if (widthFactor < heightFactor)   {    thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;   }  }  UIGraphicsBeginImageContext(targetSize); // this will crop  CGRect thumbnailRect = CGRectZero;  thumbnailRect.origin = thumbnailPoint;  thumbnailRect.size.width= scaledWidth;  thumbnailRect.size.height = scaledHeight;  [sourceImage drawInRect:thumbnailRect];  newImage = UIGraphicsGetImageFromCurrentImageContext();  if(newImage == nil)   NSLog(@"could not scale image");  //pop the context to get back to the default  UIGraphicsEndImageContext();  return newImage; }

很久之前写了一篇文章解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题。这个我记得当时从服务器拿到的照片大概有10几M的样子，加载出来会导致内存警告。所以我当时通过修改SDWebImage源码，就是把下载下来的照片进行缩放，内存就降下来了。一般情况下应该不会加载这么大的照片的，用户要是知道，早把你的APP给删掉了。

正文到此结束