Text widget in Flutter shows same text for all Text widgets in for loop-CodePudding

In Flutter, I am using a Text widget in a for loop. The console shows a nice increasing list of numbers. However all 25 Text widgets show 25.

It looks like the Text widget does make a reference to _markersDistanceCount instead of using their value.

I've also tried to jsonEncode and jsonDecode the values, but still they are all 25. Does anyone know what I am doing wrong?

var _markersDistanceCount = 0;
for (var i = 0; i < 25; i  ) {
  _markersDistanceCount  ;
  print(_markersDistanceCount);
  markersDistance.add(
    Marker(
      point: LatLng(point.latitude, point.longitude),
      builder: (context) => CircleAvatar(
        radius: 50,
        backgroundColor: Colors.red,
        child: Text(_markersDistanceCount.toString())
      ),
    ),
  );
}

When I change Text(_markersDistanceCount.toString()) to Text(i.toString()) there is no issue and Text widgets are containing the correct i value.

CodePudding user response：

I assume you end up with all having 25 as Text. The Text() have the same variable the whole time.

UPDATE:

The Text(_markersDistanceCount) you have is all pointing to the same variable, which in the end have the value of 25.

Try this instead:

for (var i = 0; i < 25; i  ) {
  // Either
  final _distanceCount = _markersDistanceCount  ;
  // Or rather
  final _distanceCount =  i   1;

  markersDistance.add(
    Marker(
      point: LatLng(point.latitude, point.longitude),
      builder: (context) => CircleAvatar(
        radius: 50,
        backgroundColor: Colors.red,
        child: Text(_distanceCount.toString())
      ),
    ),
  );
}

CodePudding user response：

The value of _markersDistanceCount becomes 25 before reaching the Marker's builder method. To explore it I've debugged the code, here I am using an inline method to show the situation. I am not aware of this type of behavior, just exploring the issue.

@override
void initState() {
  super.initState();
  int _markersDistanceCount = 0;
  for (int i = 0; i < 25; i  ) {
    _markersDistanceCount  ;
    markersDistance.add(
      () {
        debugPrint("OnTop=>  i: $i mkNUm:  ${_markersDistanceCount.toInt()}");
        return Marker(
            key: ValueKey("tm $_markersDistanceCount"),
            point: () {
              debugPrint(
                  "On point=>  i: $i mkNUm:  ${_markersDistanceCount.toInt()}");
              return LatLng(51.5   (i * .01), -0.09);
            }(),
            builder: (context) {
              ///this gets call after while `_markersDistanceCount:25` completing the loop
              debugPrint(
                  "insideBuild=> i: $i mkNUm:  ${_markersDistanceCount.toInt()}");
              return CircleAvatar(
                radius: 50,
                backgroundColor: Colors.red,
                child: Text(
                  _markersDistanceCount.toDouble().toString(),
                ),
              );
            });
      }(),
    );
  }
}

This will print

OnTop=>  i: 0 mkNUm:  1
On point=>  i: 0 mkNUm:  1
OnTop=>  i: 1 mkNUm:  2   
On point=>  i: 1 mkNUm:  2
OnTop=>  i: 2 mkNUm:  3   
.....
OnTop=>  i: 24 mkNUm:  25
On point=>  i: 24 mkNUm:  25
insideBuild=> i: 0 mkNUm:  25
insideBuild=> i: 1 mkNUm:  25

As for the solution, you can use i while both share the same responsibility.