Unable to add key and bool value into nested list - flutter

Question

Example Code (Not working):
void main() {
List json = [
{
"sku": "SKU0001",
"uids": [
{
"uid": "U001"
}
]
}
];
var result = json.map( (item) {
item['no_desc'] = true; // able to add the key and bool value
item['uids'] = item['uids'].map( (uid) {
uid['is_scanned'] = true; // failed to add, but able to accept string value only.
return uid;
}).toList();
return item;
}).toList();
print(result);
}
return error 'bool' is not a subtype of type 'String'
Expected Result
[
{
sku: SKU0001,
no_desc: true,
uids: [
{
uid: U001,
is_scanned: true // must be boolean
}
]
}
]
It work when i try in String value.
uid['is_scanned'] = 'true';
How can I add bool value into the nested list?
If I am writing in javascript way,
it should be able to add the key into nested array ( list ).
But why in dart lang, it prompt me error?
Can someone expert in dart lang willing to explain to me?

Answer 1

Your issue can be fixed by creating a new Map instance in the inner .map method with the Map.from constructor.
item['uids'] = item['uids'].map( (uid) {
uid['is_scanned'] = true; // failed to add, but able to accept string value only.
return uid;
}).toList();
should be changed to:
item['uids'] = item['uids'].map( (uid) {
Map<String, dynamic> toReturn = Map.from(uid);
toReturn['is_scanned'] = true;
return toReturn;
}).toList();
I believe this issue is due to dart implicitly declaring the inner uids maps as Map<String, String> so creating a new instance changes this and allows you to assign any value to the keys of the Map.
Full working sample:
void main() {
List json = [
{
"sku": "SKU0001",
"uids": [
{
"uid": "U001"
}
]
}
];
var result = json.map( (item) {
item['no_desc'] = true;
item['uids'] = item['uids'].map( (uid) {
Map<String, dynamic> toReturn = Map.from(uid);
toReturn['is_scanned'] = true;
return toReturn;
}).toList();
return item;
}).toList();
print(result);
}