handleAddToList = () => {
    let items = [...this.state.items];
    let lastId = Math.max.apply(null, items.id);
    let newId = lastId + 1;

    items.filter(i => i.title == this.state.text).length === 1
      ? alert("This item is on the list already.")
      : items.push({
          id: newId,
          title: this.state.text,
          found: 0,
          value: 0,
          icon: "delete"
        });
   this.setState({ items: items });
  };

<Input
 placeholder="Start typing"
 label={"Your next shop list item..."}
 onChangeText={text => this.setState({ text })}
/>
<Button title="Add to list" onPress={() => this.handleAddToList()} />

Warning: Encountered with two children with the same key, '"-infinity"'.

<ListItem
 key={l.id}
 title={l.title}
 rightIcon={{ name: l.icon, color: "#cc0033" }}
 bottomDivider={true}
/>