go语言设计模式之observer

Posted 2020-11-22 aguncn

observer.go

package observer

import (
	"fmt"
)

type Observer interface {
	Notify(string)
}

type Publisher struct {
	ObserversList []Observer
}

func (s *Publisher) AddObserver(o Observer) {
	s.ObserversList = append(s.ObserversList, o)
}

func (s *Publisher) RemoveObserver(o Observer) {
	var indexToRemove int
	for i, observer := range s.ObserversList {
		if observer == o {
			indexToRemove = i
			break
		}
	}
	s.ObserversList = append(s.ObserversList[:indexToRemove], s.ObserversList[indexToRemove+1:]...)
}

func (s *Publisher) NotifyObservers(m string) {
	fmt.Printf("Publisher received message ‘%s‘ to notify observers
", m)
	for _, observer := range s.ObserversList {
		observer.Notify(m)
	}
}

　　

observer_test.go

package observer

import (
	"fmt"
	"testing"
)

type TestObserver struct {
	ID      int
	Message string
}

func (p *TestObserver) Notify(m string) {
	fmt.Printf("Observer %d: message ‘%s‘ received 
", p.ID, m)
	p.Message = m
}

func TestSubject(t *testing.T) {
	testObserver1 := &TestObserver{1, ""}
	testObserver2 := &TestObserver{2, ""}
	testObserver3 := &TestObserver{3, ""}

	publisher := Publisher{}

	t.Run("AddObserver", func(t *testing.T) {
		publisher.AddObserver(testObserver1)
		publisher.AddObserver(testObserver2)
		publisher.AddObserver(testObserver3)

		if len(publisher.ObserversList) != 3 {
			t.Fail()
		}
	})

	t.Run("RemoveObserver", func(t *testing.T) {
		publisher.RemoveObserver(testObserver2)

		fmt.Println(publisher.ObserversList)

		if len(publisher.ObserversList) != 2 {
			t.Error("The size of the observer list is not 2.")
		}

		for _, observer := range publisher.ObserversList {
			testObserver, ok := observer.(*TestObserver)
			if !ok {
				t.Fail()
			}
			if testObserver.ID == 2 {
				t.Fail()
			}
		}
	})

	t.Run("Notify", func(t *testing.T) {
		for _, observer := range publisher.ObserversList {
			printObserver, ok := observer.(*TestObserver)
			if !ok {
				t.Fail()
				break
			}
			if printObserver.Message != "" {
				t.Error("The observer‘s Message field weren‘t empty.")
			}
		}

		message := "Hello World"
		publisher.NotifyObservers(message)

		for _, observer := range publisher.ObserversList {
			printObserver, ok := observer.(*TestObserver)
			if !ok {
				t.Fail()
				break
			}
			if printObserver.Message != message {
				t.Errorf("Expected message on observer %d was "+
					"not expected: ‘%s‘ != ‘%s‘
", printObserver.ID,
					printObserver.Message, message)
			}
		}
	})
}