Not able to get element index in a listview - Flutter - flutter

Question

i'm trying to make operations on clicked elements in a listView in flutter. An alertDialog should appear once I click an element so I can update its value. My backend works perfectly using the put http method. The problem is that i'm able to read the input value in console but not able to read the index of the clicked element.
As it's mentionned above, i'm able to read the input value which means that my api works correctly, but not able to retrieve the clicked element's index in the listView.
Console output:
I/flutter ( 4120): ============================== null
I/flutter ( 4120): 33
here is my update function:
handleMeasurement(String iv_id, String value) async {
final response = await http.put(
Uri.parse('${baseUrl}/api/v1/measurements/update/' + iv_id),
body: <String, String>{
"input_value": value
});
}
and here is my ui:
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
automaticallyImplyLeading: false,
title: Text(
'Traitement des mesures',
style: TextStyle(color: Colors.black),
),
centerTitle: true,
),
body: Visibility(
visible: isLoaded,
replacement: Center(child: CircularProgressIndicator()),
child: Column(
children: <Widget>[
Expanded(
child: ListView.builder(
padding: EdgeInsets.all(15),
itemCount: mesures?.length,
itemBuilder: (BuildContext context, int index) {
return GestureDetector(
onTap: () => showDialog<String>(
context: context,
builder: (BuildContext context) => AlertDialog(
title: const Text('Mesure'),
content: TextField(
controller: _textFieldController,
decoration:
InputDecoration(hintText: "Entrez la valeur"),
),
actions: <Widget>[
TextButton(
onPressed: () => Navigator.pop(context, 'Cancel'),
child: const Text('Cancel'),
),
TextButton(
onPressed: () => {
print(
"============================== ${mesures![index].measurement_id}"),
print(_textFieldController.text),
handleMeasurement(
"${mesures![index].measurement_id}",
_textFieldController.text),
Navigator.pop(context, 'OK')
},
child: const Text('OK'),
),
],
),
),
child: Container(
margin: EdgeInsets.only(bottom: 15),
child: Row(
children: [
SizedBox(
width: 70,
child: AspectRatio(
aspectRatio: 0.88,
child: Container(
decoration: BoxDecoration(
color: Color(0xFFF5F6F9),
borderRadius: BorderRadius.circular(15),
),
child: Image.asset(
'assets/note2.png',
),
),
),
),
SizedBox(width: 20),
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
"Paramètre: ${mesures![index].param_name}",
style: TextStyle(
color: Colors.black, fontSize: 16),
maxLines: 2,
),
SizedBox(height: 10),
Text.rich(
TextSpan(
text:
"Description: ${mesures![index].description}",
style: TextStyle(
fontWeight: FontWeight.w600,
color: kPrimaryColor),
),
),
],
),
],
),
),
);
},
),
)
],
),
),
);
}
Can anyone help me out with it? thanks in advance!