iOS 图片压缩

有时候从App上传图片给后台，由于图片较大, 需要将图片压缩一下。

压缩的时候注意有的方案会卡线程，耗时。

这里有个方案：不耗时，不卡线程

-(UIImage *)makeThumbnailFromImage:(UIImage *)srcImage scale:(double)imageScale{
    
    UIImage *thumbail = nil;
    CGSize imageSize = CGSizeMake(srcImage.size.width*imageScale, srcImage.size.height*imageScale);
    
    if (srcImage.size.width != imageSize.width || srcImage.size.height != imageSize.height) {
        UIGraphicsBeginImageContext(imageSize);
        CGRect imageRect = CGRectMake(0, 0, imageSize.width, imageSize.height);
        
        [srcImage drawInRect:imageRect];
        thumbail = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        
    }
    else{
        thumbail = srcImage;
    }
    return thumbail;
    
}

参考自：https://www.cnblogs.com/ChouDanDan/p/5038396.html#commentform