iOS与H5交互 询问相机、相册权限的问题

问题背景：
某个H5页面中需要打开手机本地相册及照相机，用户选择某几张图片之后上传至服务器上。纯H5完成的话，当打开相机或者相册时，第一次会正常询问权限，但是如果用户点击了不允许之后，询问弹窗不再能弹出，H5处理不了。

当然简单粗暴地方式就是改为纯原生来写，不过我们的页面已用了很久，只是新增了一个上传的功能，所以还是延续当前页面，只不过改为原生和H5交互的方式，即e页面仍是H5页面，打开相册相机的弹窗改为由原生代码处理，最后将用户选择到的图片传给H5，由H5将数据传给服务端。

中间的交互不再赘述，网上到处都是，只是最后将拿到的数据传给H5这一步有一个小小的坑需注意;

第一步，将图片转化成字符串：

//当我们拿到图片之后，会将图片image转化成字符串
  NSString *imageStr = [self encodeImageToBase64:image];
//将上述合法的字符串传给H5
[self p_toJSPramaWithImageBase64Str:imageStr];

此处，压缩转化中，base64EncodedStringWithOptions的options必须传NSDataBase64EncodingEndLineWithCarriageReturn，否则会失败！！！

//  将image转成5兆以内的二进制流，然后转化成base64的字符串
//  #define ImageMaxLength 1024.0*1024.0*5  //5M
- (NSString *)encodeImageToBase64:(UIImage *)image {
    NSData *imageData = [image compressWithMaxLength:ImageMaxLength];
    return  [imageData base64EncodedStringWithOptions:NSDataBase64EncodingEndLineWithCarriageReturn];
}

压缩图片

//压缩到多少以内 1024.0*1024.0*5 5兆以内
-(NSData *)compressWithMaxLength:(NSUInteger)maxLength
{
    // Compress by quality
    CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(self, compression);
    //NSLog(@"Before compressing quality, image size = %ld KB",data.length/1024);
    if (data.length < maxLength) return data;
    
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(self, compression);
        //NSLog(@"Compression = %.1f", compression);
        //NSLog(@"In compressing quality loop, image size = %ld KB", data.length / 1024);
        if (data.length < maxLength * 0.9) {
            min = compression;
        } else if (data.length > maxLength) {
            max = compression;
        } else {
            break;
        }
    }
    //NSLog(@"After compressing quality, image size = %ld KB", data.length / 1024);
    if (data.length < maxLength) return data;
    UIImage *resultImage = [UIImage imageWithData:data];
    // Compress by size
    NSUInteger lastDataLength = 0;
    while (data.length > maxLength && data.length != lastDataLength) {
        lastDataLength = data.length;
        CGFloat ratio = (CGFloat)maxLength / data.length;
        //NSLog(@"Ratio = %.1f", ratio);
        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);
        //NSLog(@"In compressing size loop, image size = %ld KB", data.length / 1024);
    }
    //NSLog(@"After compressing size loop, image size = %ld KB", data.length / 1024);
    return data;
}

第二步将数据传给H5：
iosSelectImageSuc为和h5约定好的方法
此处要点：字符串必须要拼接 data:image/jpg;base64,否则依然会失败！！！！

- (void)p_toJSPramaWithImageBase64Str:(NSString *)imageBase64Str {
    //oc调js，将图片传给H5
    NSString *str = [@"data:image/jpg;base64," stringByAppendingString:imageBase64Str];
    NSString *jsStr = [NSString stringWithFormat:@"%@('%@')",@"iosSelectImageSuc",str];
    [self.webView evaluateJavaScript:jsStr completionHandler:^(id _Nullable result, NSError * _Nullable error) {
        NSLog(@"%@--%@",result,error);
    }];
       
}