State Pattern
The state pattern is used in computer programming to encapsulate varying behavior for the same object, based on its internal state. This can be a cleaner way for an object to change its behavior at runtime without resorting to conditional statements and thus improve maintainability.
Example
abstract class State {
void handler(Stateful context);
String toString();
}
class StatusOn implements State {
handler(Stateful context) {
print(" Handler of StatusOn is being called!");
context.state = StatusOff();
}
@override String toString() {
return "on";
}
}
class StatusOff implements State {
handler(Stateful context) {
print(" Handler of StatusOff is being called!");
context.state = StatusOn();
}
@override String toString() {
return "off";
}
}
class Stateful {
State _state;
Stateful(this._state);
State get state => _state;
set state(State newState) => _state = newState;
void touch() {
print(" Touching the Stateful...");
_state.handler(this);
}
}
void main() {
var lightSwitch = Stateful(StatusOff());
print("The light switch is ${lightSwitch.state}.");
print("Toggling the light switch...");
lightSwitch.touch();
print("The light switch is ${lightSwitch.state}.");
}