How – Compare 2 arrays of different lengths and look for matching values – Flutter

Issue

Im not sure if my strategy or logic is correct to achieve this, but I have 2 Lists coming from 2 different jsondata mysql quieries, lets say they look like this:

List newsAgency = [{id: 1, name: 9news, image: x} 
                   {id: 2, name: abcnews, image: y} 
                   {id: 3, name: bbcnews, image:z}];

List following = [{userid: 41, username: x, newsid: 2}
                  {userid: 41, username: x newsid: 3}];

I want to see if the id in newsAgency matches the newsid in following list, and to return true or false correspondingly.

The idea is to say that I am following 2 news agencies out of 3, so my goal is to display the button to follow or unfollow based on the results.

I tried everything suggested from this post how can I find a list contains in any element another list in flutter? but couldnt get it.

This is my code example:

Listview.builder(
  itemCount: newsAgency.length,
  itemBuilder: (BuildContext context, int index) {
    bool following = false;
    return Card(
        elevation: 10.0,
        child: Row(
            children: [
                Text(newsAgency[index]['name'],
                following 
                ? TextButton(onPressed: () {//unfollow function},
                            child: const Text('unfollow')),
                : TextButton(onPressed: () {//follow function},
                            child: const Text('follow')),
                ]));});

Any help is highly appreciated

Solution

add this method in your class, it will be responsible for searching which items are following and which are not, and return a bool based on it:

  bool checkIsFollowing(Map<String, dynamic> current) {
    for(int index = 0; index < following.length; index+=1) {
      if(current["id"] == following[index]["newsid"]) {
        return true;
      }
    }
    return false;
  }

now inside of your ListView‘s itemBuilder, replace this:

    bool following = false;

with this:

 final currentNewsAgency = newsAgency[index];
 bool following = checkIsFollowing(currentNewsAgency);
 

following will be true or false based on if the current Agency’s id exists in some item in the following list.

Answered By – Gwhyyy

Answer Checked By – David Goodson (FlutterFixes Volunteer)