Question

我已经使用函数作为观察者实现了观察者模式，它似乎按预期工作：

const subjectElem       = document.getElementById('subject');
const observerOneElem   = document.getElementById('observer-1');
const observerTwoElem   = document.getElementById('observer-2');
const subscribeOneElem  = document.getElementById('subscribe-1');
const subscribeTwoElem  = document.getElementById('subscribe-2');

const subject   = new Subject();

// Using functions as Observers
const observer1 = function (data) {
  observerOneElem.value = data;
};

const observer2 = function (data) {
  observerTwoElem.value = data;
};

subscribeOneElem.addEventListener('change', event => {
  if (event.target.checked) {
    subject.add(observer1);
  } else {
    subject.remove(observer1);
  }
});

subscribeTwoElem.addEventListener('change', event => {
  if (event.target.checked) {
    subject.add(observer2);
  } else {
    subject.remove(observer2)
  }
});

subjectElem.addEventListener('keyup', event => {
  // notify all subscribed observers
  subject.setState(event.target.value);
});

function Subject() {
  this.observers = [];            // observers list
  this._state = '';
}

Subject.prototype.add = function (observer) {
  this.observers.push(observer);
}

Subject.prototype.remove = function (observer) {
  let i = 0;
  while (i < this.observers.length) {
    if (this.observers[i] === observer)
      break;
    i++;
  }
  this.observers.splice(i, 1);
}

Subject.prototype.setState = function (data) {
  this._state = data;
  this.observers.forEach(observer => {
    observer(data);
  });
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS Sandbox</title>
  <style>
    .row {
      background-color: cornflowerblue;
      padding: 1%;
    }
  </style>
</head>
  <h1>Observer Pattern</h1>
  <div class="row">
    <form>
      <label for="subject">Subject:
        <input type="text" id="subject">
      </label>
    </form>
  </div>
  <br>
  <div class="row">
    <form>
      <label for="observer-1">Observer 1:
        <input type="text" id="observer-1">
      </label>
      <label for="subscribe-1">Subscribe:
        <input type="checkbox" id="subscribe-1" unchecked>
      </label>
    </form>
  </div>
  <br>
  <div class="row">
    <form>
      <label for="observer-2">Observer 2:
        <input type="text" id="observer-2">
      </label>
      <label for="subscribe-2">Subscribe:
        <input type="checkbox" id="subscribe-2" unchecked>
      </label>
    </form>
  </div>
  <script src="app.js"></script>
</body>
</html>

我想知道的是如何使用对象作为观察者，我的意思是如何将它们与HTML输入元素连接起来。我想到了这样的构造函数：


function Observer() {
  this.notify = function (subject) {
    let currentState = subject.getState();
    this.value = currentState;
    console.log(currentState);        // logs current state (testing)
  }
}

以及主题中的方法，如下所示：

Subject.prototype.getState = function () {
  return this._state;
}

但我看不到如何将 input 元素（observerOneElem 和 observerTwoElem）与 Observer 的实例连接起来。

Answer 1

这并不难，只需在实例化 observer 时通过传递 id 来选择 Observer 构造函数中的元素。现在它与作为对象实现的观察者一起工作。（没有小狗受到伤害，没有咨询图书馆）

const subjectElem       = document.getElementById('subject');
const subscribeOneElem  = document.getElementById('subscribe-1');
const subscribeTwoElem  = document.getElementById('subscribe-2');

const subject = new Subject();

// Using objects as Observers
const observer1 = new Observer('observer-1');
const observer2 = new Observer('observer-2');

subscribeOneElem.addEventListener('change', event => {
  if (event.target.checked) {
    subject.add(observer1);
  } else {
    subject.remove(observer1);
  }
});

subscribeTwoElem.addEventListener('change', event => {
  if (event.target.checked) {
    subject.add(observer2);
  } else {
    subject.remove(observer2)
  }
});

subjectElem.addEventListener('keyup', event => {
  // notify all subscribed observers
  subject.setState(event.target.value);
});

function Subject() {
  this.observers = [];            // observers list
  this._state = '';
}

Subject.prototype.add = function (observer) {
  this.observers.push(observer);
}

Subject.prototype.remove = function (observer) {
  let i = 0;
  while (i < this.observers.length) {
    if (this.observers[i] === observer)
      break;
    i++;
  }
  this.observers.splice(i, 1);
}

Subject.prototype.setState = function (data) {
  this._state = data;
  this.observers.forEach(observer => {
    observer.notify(this);
  });
}

Subject.prototype.getState = function () {
  return this._state;
}

function Observer(id) {
  this.observer = document.getElementById(id);
  this.notify = function (subject) {
    let currentState = subject.getState();
    this.observer.value = currentState;
  }
}

以对象为观察者的观察者模式

1 个答案: