记录-微信分享的一个坑

有这么一段代码，用来分享多媒体消息，imgurl就是服务器给过来的图片

   WXMediaMessage *message=[WXMediaMessage message];
    message.title=title;
    message.description=description;
    
    
    
    UIImage *cachedImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:imgUrl]] scale:0.1];
    

    
    [message setThumbImage: cachedImage];

一开始用jpg加载图片的时候没问题，后来图片用了png的，结果就一直显示的是分享失败

一开始以为是png图片加载不出来，后来差了文档才发现是因为 图片的尺寸过大。

解决办法，压缩图片之后再传

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize sourceImage:(UIImage *)oldImage
{
    UIImage *sourceImage = oldImage;
    
    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;
}