Resolved: flutter UI page navigation

In this post, we will see how to resolve flutter UI page navigation

Question:

PlanDaysExList is a list that has workout exercises and if the list is empty…it should navigate me to the restScreen() / if the list has exercises…it should navigate me to the getPlanExercisesScreen()
my problem is that when the list has exercises or empty…it always navigate me to the getPlanExercisesScreen() i don’t know where the problem is.
here is my code:

Widget DaysDetails(context,index,weekNum) => InkWell(
    onTap: ()
    {
      LifeStyleCubit.get(context).PlanDaysExList=[];
      LifeStyleCubit.get(context).getPlanDaysExercises(
            planName: model.planName,
            weekNum: weekNum+1,
            dayNum: index + 1,
        );
        if(LifeStyleCubit.get(context).PlanDaysExList==[])
          {Navigator.push(context, MaterialPageRoute(
              builder: (context)=>restScreen()));}
        else{Navigator.push(context, MaterialPageRoute(
            builder: (context)=>getPlanExercisesScreen()));}

    },
    child: SizedBox(
      height: 35,width: 100,
      child: Container(
        color: Colors.orange,
        child: Center(child: Text('Day ${index+1}')),
      ),
    ),
  );

void getPlanDaysExercises({
    required int weekNum, required int dayNum,
    required String planName,
  })
  {
    FirebaseFirestore.instance
        .collection('users')
        .doc(uId)
        .collection('plans')
        .doc(planName)
        .collection('week $weekNum')
        .doc('week $weekNum')
        .collection('days')
        .get()
        .then((value){
      PlanDaysExList.clear();
      value.docs.forEach((element)
      {
        if(element.data()['day'] == dayNum)
        {
          PlanDaysExList.add(PlanExercisesModel.fromJson(element.data()));
        }
      });

in the last line of code, it means that if docs.element.data[day] not matched dayNum so PlanDaysExList must be null but it still navigate me to the getPlanExercisesScreen() however when i navigate there…it doesn’t show me the exercises so that mean the list is empty! what am i missing ?

Best Answer:

The error lies in the line where you check whether the list is empty or not.

if(LifeStyleCubit.get(context).PlanDaysExList==[])

Change it to:

if(LifeStyleCubit.get(context).PlanDaysExList.isEmpty)

Tried this with a simpler example:

ElevatedButton(
  onPressed: () {
    //Change this if condition check
    if (list1.isEmpty) {
      log('List is empty.');
    } else {
      log('List is not empty.');
    }
  },
  child: const Text('Press'),
),

where I replaced the if(list1 == [] (in your case) with isEmpty method of the list.
The reason is that you can not compare lists like you’d do in Python, without checking for ListEquality (imported from collection.dart):

import 'package:collection/collection.dart';
final list1 = [];
final Function listEquality = const ListEquality().equals;

@override
Widget build(BuildContext context) {
  return ElevatedButton(
    onPressed: () {
      //This if now validates
      if (listEquality(list1, [])) {
        log('empty');
      } else {
        log('not empty');
      }
    },
    child: const Text('Press'),
  );
}

If you have better answer, please add a comment about this, thank you!

Source: Stackoverflow.com

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