【转】ios开发之生成所缩略图方式

亲测：两种方式都有效

第一种方式：缩略成固定的尺寸大小

 - (UIImage *)thumbnailWithImageWithoutScale:(UIImage *)image size:(CGSize)asize
 {
     UIImage *newimage;
     if (nil == image) {
         newimage = nil;
     } else {
         UIGraphicsBeginImageContext(asize);
         [image drawInRect:CGRectMake(, , asize.width, asize.height)];
         newimage = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();
     }
     return newimage;

 }

第二种方式：保持原来图片的宽高比

 - (UIImage *)thumbnailWithImageWithoutScale:(UIImage *)image size:(CGSize)asize
 {
     UIImage *newimage;
     if (nil == image) {
         newimage = nil;
     }
     else{
         CGSize oldsize = image.size;
         CGRect rect;
         if (asize.width/asize.height > oldsize.width/oldsize.height) {
             rect.size.width = asize.height*oldsize.width/oldsize.height;
             rect.size.height = asize.height;
             rect.origin.x = (asize.width - rect.size.width)/;
             rect.origin.y = ;
         }
         else{
             rect.size.width = asize.width;
             rect.size.height = asize.width*oldsize.height/oldsize.width;
             rect.origin.x = ;
             rect.origin.y = (asize.height - rect.size.height)/;
         }
         UIGraphicsBeginImageContext(asize);
         CGContextRef context = UIGraphicsGetCurrentContext();
         CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);
         UIRectFill(CGRectMake(, , asize.width, asize.height));//clear background
         [image drawInRect:rect];
         newimage = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();
     }
     return newimage;
 }