(forwarding articles) after skipping multiple pages, shuttle returns to the first page and passes parameters

Link to the original text ：https://blog.csdn.net/u013491829/article/details/105313600
Event distribution EventBus Tool class

// Subscriber callback signature 
typedef void EventCallback(arg);
 
class EventBus {
    
  // Private constructor 
  EventBus._internal();
 
  // Save single example 
  static EventBus _singleton = new EventBus._internal();
 
  // Factory constructor 
  factory EventBus()=> _singleton;
 
  // Save the event subscriber queue ,key: Event name (id),value:  Subscriber queue corresponding to the event 
  var _emap = new Map<Object, List<EventCallback>>();
 
  // Add subscribers 
  void on(eventName, EventCallback f) {
    
    if (eventName == null || f == null) return;
    _emap[eventName] ??= new List<EventCallback>();
    _emap[eventName].add(f);
  }
 
  // Remove subscribers 
  void off(eventName, [EventCallback f]) {
    
    var list = _emap[eventName];
    if (eventName == null || list == null) return;
    if (f == null) {
    
      _emap[eventName] = null;
    } else {
    
      list.remove(f);
    }
  }
 
  // Triggering event , After the event is triggered, all subscribers of the event will be called 
  void emit(eventName, [arg]) {
    
    var list = _emap[eventName];
    if (list == null) return;
    int len = list.length - 1;
    // Reverse traversal , Prevent subscribers from removing subscript misalignment caused by themselves in the callback  
    for (var i = len; i > -1; --i) {
    
      list[i](arg);
    }
  }
}
 
// Define a top-level（ overall situation ） Variable , The page can be used directly after importing the file bus
var bus = new EventBus();

Use event distribution

//Page 1、2、3、4 in 
...
 
bus.on(" Tag of agreed enjoyment event ", (arg) {
    
  // do something
});
 Send parameters to the subscription interface 
...
//
bus.emit(" Tag of agreed enjoyment event ", " Parameters passed ");