Issue with callback - flutter

Question

I would like to create a generic dialog but I have some issue with the callback... Here is my code :
The dialog :
class ConfirmDialog {
static Future show<T>(BuildContext context, String message,
void Function(T) onConfirm, VoidCallback? onRefuse) {
return showDialog(
context: context,
builder: (context) {
return Container(
alignment: Alignment.center,
decoration: BoxDecoration(
color: Colors.grey[300],
),
child: Container(
padding: EdgeInsets.fromLTRB(0, 20, 0, 0),
width: 400,
height: 200,
child: Card(
child: Column(
children: [
Text(
message,
textAlign: TextAlign.center,
style: TextStyle(fontSize: 30),
),
Container(
margin: EdgeInsets.fromLTRB(0, 20, 0, 0),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
GestureDetector(
child: Container(
height: 70,
padding: EdgeInsets.fromLTRB(0, 0, 20, 0),
child: Image.asset("assets/images/confirm.png"),
),
onTap: () => {
onConfirm,
print("accept"),
Navigator.pop(context),
}),
GestureDetector(
child: Container(
height: 70,
padding: EdgeInsets.fromLTRB(20, 0, 0, 0),
child: Image.asset("assets/images/cancel.png"),
),
onTap: () => {
if (onRefuse != null)
{
onRefuse,
}
else
{
Navigator.pop(context),
}
print("refuse")
},
),
],
),
),
],
),
),
),
);
},
);
}
The widget :
Widget listView(List<Product> products) {
return ListView.builder(
itemCount: products.length,
itemBuilder: (context, index) {
Product product = products[index];
return GestureDetector(
child: Container(
height: 150,
child: Card(
child: Row(
children: [
Container(
alignment: Alignment.center,
padding: EdgeInsets.fromLTRB(5, 10, 5, 10),
width: 150,
height: 150,
child: Image.network(product.small),
),
Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
product.name,
overflow: TextOverflow.ellipsis,
maxLines: 1,
softWrap: false,
style: TextStyle(
fontSize: 30,
),
),
Text(
product.getBrand(),
style: TextStyle(
color: Colors.grey,
fontSize: 25,
fontFamily: "Antonio",
),
)
],
),
)
],
),
),
),
onTap: () => {},
onLongPress: () => {
ConfirmDialog.show<Product>(
context,
"Are you sure you want to delete\n${product.name} ?",
deleteSelectedProduct(product),
null,
)
},
);
},
);
}
Everytime I "longpress", I got this error message :
The following _TypeError was thrown while handling a gesture: type
'Null' is not a subtype of type '(Product) => dynamic'
The product I pass as parameter is not null and the dialog don't show up but the method "deleteSelectedProduct" is triggered.
I can't figure out where I got it wrong?
If someone can help, it would be great!
Thank you in advance

Answer 1

The function is being called before it is passed in, so it will return null and pass that value in. You would need to use deleteSelectedProduct instead of deleteSelectedProduct(product)