Add Item to a List Dynamically

[Andrew Villegas]

Hi Flutter Community,

I'm trying to add items to a Lis<dynamic> dynamically. This is how I declared my list.

List<dynamic> ingredientes = [];

I'm then assigning values from Firestore to this List, inside initState(),

ingredientes = widget.productId.data()['ingredientesArray'];

Finally,  I'm using a ListView.builder to construct and display this List, returning the 'Text' 

for each element here.

ListView.builder(
shrinkWrap:
true,
physics:
NeverScrollableScrollPhysics(),
itemCount: ingredientes.length,
itemBuilder:
(context,
index) {
return...

-----------------------------------------------------------------------------------------

Everything works fine so far... except that when I try to add items dynamically to this list, from another List, I get the following error: RangeError (index): Invalid value: Not in inclusive range 0..5: 7

This is how I'm trying this:

//A few things to note here:

//1:  'ingredientes' is the List I want to add to

//2: snapshot.data.docs is my 2nd List..

//3:  'snapshot.data.docs' is a List<String>, so in Theory I think this should match the <dynamic> type of ingredientes

//4: If I remove the line " ingredientes.add(snapshot.data.docs[index]);"   and simply have the  " ingredientes.length = ingredientes.length + 1"  &. the line  ""print (ingredientes.length);"  , the length of ingredientes actually increases after I tap an item of my 'snapshot.data.docs' list. (Please refer to my screenshots attached here).

But when I have the following lines, I get the error mentioned above... (RangeError (index): Invalid value: Not in inclusive range 0..5: 7):

return GestureDetector(
onTap: () {
setState(() {
ingredientes.length = ingredientes.length + 1;
ingredientes.add(snapshot.data.docs[index]);
});
print(ingredientes
.length);
},

-------------------------------------------

It's as if the ListView.builder cannot rebuild itself, even though I'm increasing the number of "itemCount" by 1 every time I want to add a new String (and adding the String).

If this indeed is my error, how can I solve it so that my ListView.builder changes dynamically and I can add a String dynamically?

Thanks, and all best,

A.V.

[Suzuki Tomohiro]

Do you know which variable is having the list which is smaller than the index?

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[Andrew Villegas]

I think it's my ingredientes list, given that this is the list I'm using for my ListView.builder.

[Suzuki Tomohiro]

I think it's "snapshot.data.docs" that is shorter than index. Would you use breakpoints and the debugger to see which list is throwing the error?

[Andrew Villegas]

(to the whole group)

Thanks for replying, Suzuki.

Sure thing, I'll use the breakpoints and debugger right now, although I thought this line would ensure they were of equal length

ingredientes = widget.productId.data()['ingredientesArray'];

--A.V.

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[Andrew Villegas]

I figured out what my mistake was, Suzuki. It was rather a silly one (I was displaying my 'snapshot' list instead of my ingredientes list). Therefore, when I removed one item from ingredientes the indexes didn't quite match because I was reading the wrong list. 

Again, super silly.

Thank you so much for helping me figure this out though! It means a lot.

All best, and have a good night,

A.V. 

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