Check if ListView.builder returns only empty Containers

Question

I am having a list presented by a ListView.builder and I use a Function to check if an object in the list is being searched, but I want to present a screen when no object was found. So the user knows that nothing was found but I am strugelling with it, the code looks something like that:

Container OnlyShow = Container(
    child: ListView.builder(
      itemCount: myList.length,
      itemBuilder: (context, index) {
        if (searchfunction(myList[index]) == true) {
          return myListObject(myList[index]);
        } else {
          return Container(height: 0, width: 0,);
        }
      },
    ),
  );

The search function itself is not the problem I only want to know how I could find out if the ListView.builder only returns empty containers, because that would mean that no objects equal the search and therefore nothing was found.

I have tried something like that:

Container OnlyShow = Container(
    child: ListView.builder(
      itemCount: myList.length,
      itemBuilder: (context, index) {
        if (searchfunction(myList[index]) == true) {
          if (howManyObjectsAreFalse > 0) {
            howManyObjectsAreFalse--;
            dismissNoResultsFoundScreen();
          }
          return myListObject(myList[index]);
        } else {
          if (howManyObjectsAreFalse < myList.length) {
            howManyObjectsAreFalse++;
          }
          if (howManyObjectsAreFalse == myList.length) {
            showNoResultsFoundScreen();
          }
          return Container(height: 0, width: 0,);
        }
      },
    ),
  );
  
  int howManyObjectsAreFalse = 0;

It should work like this when an empty Container is returned the count is incremented and when a Result is returned the count is decreased, So when the count hits the length of the list the NoResultScreen is being presented.

It does work but with some weird exceptions, sometimes the count seems to fluctuate between to values, even if the ListView.builder only returns empty Containers.

Note: The List is not empty I just return an empty container for every object in the list that is not equal to the search value. So I don't decrease the list or something

I hope someone can help me with a better way to achieve this.

No nothing is found: when only empty containers are returned, myList remains the same, I dont't change myList i only look if searchfunction(myList) == true and if i return myList[index] and if not i return an empty Container — tims
– tims, Commented Jan 19, 2021 at 7:30
child: myList.where(searchfunction).isEmpty ? Text('nothing was found') : ListView.builder(...) — pskink
– pskink, Commented Jan 19, 2021 at 7:31
but honestly returning such Container(height: 0, width: 0,); is wrong: you should remove non existing data, and not showing empty widgets — pskink
– pskink, Commented Jan 19, 2021 at 7:42
btw cannot you use a tmp array like: final tempArray = myList.where(searchfunction).toList(); ? and use it: tempArray.isEmpty? Text('nothing found') : ListView.builder(itemCount: tempArray.length, ... — pskink
– pskink, Commented Jan 19, 2021 at 7:59

tims · Accepted Answer · 2021-01-19 08:24:20Z

3

The answer that @pskink gave did the trick:

child: myList.where(searchfunction).isEmpty ? Text('nothing was found') : ListView.builder(...)

answered Jan 19, 2021 at 8:24

tims

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1 Comment

pskink Over a year ago

btw if you really want to go that way and use "invisible" containers then you could use faster (and using less memory) method: child: myList.any(searchfunction) ? ListView.builder(...) : Text('nothing was found')

Sam Chan · Accepted Answer · 2021-01-19 07:42:37Z

2

I don't sure this is what you want

int howManyObjectsAreFalse = myList.length;
Container OnlyShow = Container(
    child: ListView.builder(
      itemCount: myList.length,
      itemBuilder: (context, index) {
        if (searchfunction(myList[index]) == true) {
            howManyObjectsAreFalse--;
          if (howManyObjectsAreFalse < myList.length) {
            dismissNoResultsFoundScreen();
          }
          return myListObject(myList[index]);
        } else {
          if (howManyObjectsAreFalse == myList.length) {
            showNoResultsFoundScreen();
          }
          return Container(height: 0, width: 0,);
        }
      },
    ),
  );

answered Jan 19, 2021 at 7:42

Sam Chan

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Comments

A. Tratseuski · Accepted Answer · 2021-01-19 08:13:10Z

1

ListView.builder is a lazy list builder, so it will only build children which are currently rendered on the screen. u could do smth like this though.

  int searchResultsCnt = 0;
  final shownList = myList.map<Widget>((e) {
    if (searchFunction(e)) {
      searchResultsCnt++;
      return myListObject(e);
    }
    return Container(height: 0, width: 0);
  }).toList<Widget>();
  
  if (searchResultsCnt == 0)
    showNoResultsFoundScreen();
  else
    dismissNoResultsFoundScreen();
  
  return ListView.builder(
    itemCount: shownList.length,
    itemBuilder: (context, index) => shownList[index],
  );

answered Jan 19, 2021 at 8:13

A. Tratseuski

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Comments

Suresh B B · Accepted Answer · 2021-12-17 09:38:31Z

ListView.builder Example when itemCount has no data to show text in body,

if (customerRegList.length != 0) {
      return ListView.builder(
          shrinkWrap: true,
          scrollDirection: Axis.vertical,
          itemCount: customerRegList == null ? 0 : customerRegList.length,
          itemBuilder: (BuildContext context, int index) {
            return Card(
child:Text('Hello World'),
 );
          });
    } else {
      return Center(
        child: Padding(
          padding: const EdgeInsets.only(top: 80.0),
          child: Text(
            'No Data Available!!',
            style: TextStyle(color: Colors.red, fontSize: 20.0, fontWeight: FontWeight.bold),
          ),
        ),
      );
    }

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