Using List to store and find class element with random member variable - flutter

Question

I want to store a class in a List to later retrieve the value. Now the problem I
m having is that one of the members is a random value. So when trying to retrieve the entry I can't find it, since I can't produce the 'key'.
I'm happy for suggestions on implementing this in a different way.
So this is the example class I want to store in a list:
class MyDevice{
int device;
int randomNumber;
void set(int device, int random){
this.device = device;
this.randomNumber = random;
}
}
class Handling{
final List<MyDevice> myDevicesList = new List<MyDevice>();
...
...
MyDevice dev = new MyDevice();
dev.set(device, random);
//Store entry into List
myDevicesList.add(dev);
...
...
Now I want to delete or possibly replace an entry, but I will have no way of
finding it since the random value is not known after storing above.
// Note that I have the device value supplied in a call-back, for the sake of this
// example let's just define a method for removing
void removeEntry(int device){
MyDevice dev = new MyDevice();
dev.set(device, );
myDevicesList.remove(dev);
}
How can I find / remove an entry that is a class and I only want to 'search' the list with one of the embers in the class that is stored?
Is the only solution to walk the list and make my own compare method to identify the entry by the 'device' member?

Answer 1

All you need is the removeWhere List method. You have to remove where MyDevice.device matches the argument, device.
Here's the code you requested for
void removeEntry(device) {
myDevicesList.removeWhere((element) => element.device == device);
}
Here's the full code.
import 'dart:math';
class MyDevice {
int device;
int randomNumber;
void setValue(int device, int random) {
this.device = device;
this.randomNumber = random;
}
}
class Handling {
final List<MyDevice> myDevicesList = new List<MyDevice>();
void addToList(device, random) {
MyDevice dev = new MyDevice();
dev.setValue(device, random);
myDevicesList.add(dev);
}
void removeEntry(device) {
myDevicesList.removeWhere((element) => element.device == device);
}
List<MyDevice> get list {
return myDevicesList;
}
}
void main() {
final handle = new Handling();
handle.addToList(2, Random().nextInt(5));
handle.addToList(18, Random().nextInt(4));
handle.addToList(12, Random().nextInt(9));
print("List before ${handle.list.map((element) {
return [element.device, element.randomNumber];
})}");
handle.removeEntry(18);
print("List after ${handle.list.map((element) {
return [element.device, element.randomNumber];
})}");
}
The output is
List before ([2, 1], [18, 0], [12, 7])
List after ([2, 1], [12, 7])
Here's the solution on dartpad

Answer 2

You don't know random value, so you have to manually compare and remove item from list.
Following code may help you.
In following example i added 1,2 and 5 and remove 2 after that you can see in print only 1 and 5.
class MyDevice {
int device;
int randomNumber;
void set(int device, int random) {
this.device = device;
this.randomNumber = random;
}
}
class Delet2 extends StatefulWidget {
#override
_Delet2State createState() => _Delet2State();
}
class _Delet2State extends State<Delet2> {
final List<MyDevice> myDevicesList = new List<MyDevice>();
#override
void initState() {
super.initState();
add(1);
add(2);
add(5);
delete(2);
for (int k = 0; k < myDevicesList.length; k++) {
print(myDevicesList[k].device);
}
}
add(int number) {
MyDevice dev = new MyDevice();
dev.set(number, Random().nextInt(1000));
myDevicesList.add(dev);
}
delete(int number) {
for (int i = 0; i < myDevicesList.length; i++) {
if (myDevicesList[i].device == number) {
myDevicesList.removeAt(i);
}
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(),
);
}
}