How to upsert items in Flutter

Question

I have a list

List<String> list = ['Hello']

I have TextField which has onChanged callback.

Question: How I can UPSERT an item to List when TextField triggers onChanged function

Wanted result: ['Hello', 'NewHello']

---

onChanged: (_) {
 // What I should do with list. Thanks
}

Solution

You need to check if the list length is 2, if it is then update the value at index 1; if the length is less then simply add the change to the list.

Use the add method on the list to insert the change.

Change _ to text and then within the callback:

onChanged: (text) {
     list.length == 2 ? list[1] = text : list.add(text);
}

Comments

[OMi Shah]

change _ to text and then within callback list.add(text). I mean onChanged: (text) { list.add(text); }

[Jack Spicy]

@OMi Shah it adds a lot of items because onChanged function is working, thanks

[Jack Spicy]

I want to add so only one item will stay in list

[OMi Shah]

It will keep adding every change, that's what it does!!

[OMi Shah]

then list.insert(1, text); should work.

[OMi Shah]

It will keep replacing the element at index 1 and will insert if it's empty.

[Jack Spicy]

thanks let me try that

[Jack Spicy]

Thanks, but the Insert method is not working for this situation because it inserts, and adds a new list of items even if index exist. Like in the database I need to have something like UPSERT. Upsert updates an item on a specific index

[OMi Shah]

this should work as your Wanted result: ['Hello', 'NewHello']. If you want to just update the old value with new value just pass the correct index to the old element.

[Jack Spicy]

It gives me ['Hello', 'Hell', 'Hel', 'He', 'H']

[OMi Shah]

@JackSpicy, my mistake. I have updated my answer. This will fulfill your need.

[Jack Spicy]

list is growable. So when length is increasing, it adds a new item (by your example) : list.add(text) When onChanged function triggers it gives 'Hello', 'Hell', ... again. I need function that will add an item with index, and later only update it

[OMi Shah]

That's what I gave you in my updated answer. Maybe you might have then made some mistake. Kindly edit your post and add your complete code with my solution.