parsing airtable json to flutter podo-CodePudding

I'm new in flutter and I have issue with parsing JSON on HTTP response.

I'm using Airtable backend, to store information about posts. These always contain images, and sometimes attachments - PDFs.

I built PODO, like this:

class Post {

String recordid;
String timecreated;
String title;
String content;
String imgurl;
List<Pdf>? pdf;

  Post({
    required this.recordid,
    required this.timecreated,
    required this.title,
    required this.content,
    required this.imgurl,
    required this.pdf
  });

  factory Post.fromJson(Map<String, dynamic> json) {
    return Post(
        // fields: Fields.fromJson(json['fields']),
      recordid: json['id'] as String,
      timecreated: json['createdTime'] as String,
        title: json['fields']['field1'] as String,
        content: json['fields']['field2'] as String,
        imgurl: json['fields']['IMG'][0]['url'] as String,
        pdf: json['fields']['PDF'] == null ? null : List<Map<String, dynamic>>.from(json['fields']['PDF']).map((dynamic value) => Pdf.fromJson(value)).toList()
    );
  }

Map<String, dynamic> toJson() => {
  "recordid": recordid,
  "timecreated": timecreated,
  "title": title,
  "content": content,
  "imgurl": imgurl,
  "pdf": pdf
  // "fields": List<dynamic>.from(fields.map((x) => x.toJson())),
};
}

class Pdf {

  Pdf({
    required this.url,
    required this.filename
  });

  Pdf.fromJson(Map<String, dynamic> json) :
        url = json['url'],
        filename = json['filename'];

  final String? url;
  final String? filename;
}

I'm not getting any errors, but when I'm trying to use PDF URL in UI, eg. in Text:

ListTile(title: Text(post.pdf.url)),

I'm getting error:

The property 'url' can't be unconditionally accessed because the receiver can be 'null'.

I'm aiming to create a button on a page, that is clickable when PDF URL exists. When it exists, button navigates to PDF view that use PDF URL to get and display PDF.

Any ideas?

CodePudding user response：

The pdf attribute is nullable, hence it cannot be accessed unconditionally. This is assuming you somehow have the pdf not as a list, otherwise you would need to index your list, your code is incomplete. You could try to do something like this:

  if (post.pdf != null) {
      //wrap it with a button or whatever
      return ListTile(title: Text(post.pdf!.url));
  }
  else {
      return Text('no pdf');
  }

CodePudding user response：

Well, sth seems to work, but still cannot parse pdf URL.

I'm getting Text "sth is there" when post.pdf != null and it works, but when I'm changing to get value from model using post.pdf!.url I'm getting same error:

Try correcting the name to the name of an existing getter, or defining a getter or field named 'url'. child:Text(post.pdf!.url));

Here's piece of code:

LayoutBuilder(builder: (context, constraints) {
                if(post.pdf != null){
                  return ElevatedButton(onPressed: () => Navigator.of(context).push(
                      MaterialPageRoute(builder: (context) => PDFview(pdf: [])
                      )),
                      child:Text(post.pdf!.url));
                }else{
                  return ElevatedButton(onPressed: null,
                      child:Text("no PDF"));
                }
              }
              )