在寫微信分享專案時，發現微信設定縮圖：

我們的圖片是從阿里雲那裡獲取的網路圖片，需要把網路圖片轉化為UIImage，下面就是方法：

+(UIImage *) getImageFromURL:(NSString *)fileURL

{
    UIImage * result;

    NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];

    result = [UIImage imageWithData:data];

    return result;
}
 

微信設定的縮圖要小於32KB，否則無法調起微信，而微信也沒有返回錯誤資訊，只是[WXApi sendReq:req]=NO，所以我們要壓縮小於32Kb

壓縮方法為：

#pragma mark - 壓縮圖片
+ (UIImage *)compressImage:(UIImage *)image toByte:(NSUInteger)maxLength {
    // Compress by quality
    CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(image, compression);
    if (data.length < maxLength) return image;
    
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(image, compression);
        if (data.length < maxLength * 0.9) {
            min = compression;
        } else if (data.length > maxLength) {
            max = compression;
        } else {
            break;
        }
    }
    UIImage *resultImage = [UIImage imageWithData:data];
    if (data.length < maxLength) return resultImage;
    
    // Compress by size
    NSUInteger lastDataLength = 0;
    while (data.length > maxLength && data.length != lastDataLength) {
        lastDataLength = data.length;
        CGFloat ratio = (CGFloat)maxLength / data.length;
        CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),
                                 (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank
        UIGraphicsBeginImageContext(size);
        [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
        resultImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        data = UIImageJPEGRepresentation(resultImage, compression);
    }
    
    return resultImage;
}
 

呼叫方法為：

   //縮圖要小於32KB，否則無法調起微信,32KB = 32*1024B=32678
   UIImage *pressImage = [IHUtility compressImage:picture toByte:32765];