推送功能似乎覆盖了Angular中的每个数组元素

Question

我正在尝试使用以下代码将一些对话消息推送到数组：

myConversations: IConversation[] = [];
myConversationMessage: IConversationMessages = {
conversationId: 0,
messageId: 0,
messageText: ''
};
myConversationMessages: IConversationMessages[] = [];

this.conversationService.getConversations().subscribe(conversations => {
  this.myConversations = conversations;

  for (let i of this.myConversations) {
    this.myConversationMessage.conversationId = i.conversationId;       
    for (let j of i.messages) {
      this.myConversationMessage.messageId = j.messageId;
      this.myConversationMessage.messageText = j.messageText; 
      this.myConversationMessages.push(this.myConversationMessage);
    }
  }

  console.log(this.myConversationMessages);
});

我正在从JSON对象中检索其中的对话和消息。不是将每个消息都推送到myConversationMessages数组，而是在控制台中输出以下内容：

0 
conversationId: 2
messageId:2
messageText: "testing"

1
conversationId: 2
messageId:2
messageText: "testing"

2
conversationId: 2
messageId:2
messageText: "testing"

3
conversationId: 2
messageId:2
messageText: "testing"

因此，最终的“对话”对象将覆盖每个数组元素。

有人可以告诉我为什么我的代码这样做？非常感谢提前

附：我可以上传更多代码，如果它能解决我的问题。

Answer 1

这是因为JavaScript对象通过引用传递：

myConversationMessages: IConversationMessages[] = [];

this.conversationService.getConversations().subscribe(conversations => {
  this.myConversations = conversations;

  for (let i of this.myConversations) {
    this.myConversationMessage.conversationId = i.conversationId;       
    for (let j of i.messages) {
      this.myConversationMessage.messageId = j.messageId;
      this.myConversationMessage.messageText = j.messageText; 
      this.myConversationMessages.push(this.myConversationMessage); // <-= Here you are pushing a reference to the same object in every loop. In every loop you are updating the single object, and the reference in each array spot points to the same object
    }
  }

  console.log(this.myConversationMessages);
});

试试这个：

  for (let i of this.myConversations) {
    for (let j of i.messages) {
      this.myConversationMessages.push({
          conversationId: i.conversationId,
          messageId: j.messageId,
          messageText: j.messageText
      });
    }
  }

这将为每次迭代创建一个新对象

Answer 2

发生这种情况是因为您将引用对象添加到数组在您的示例中，您没有向数组添加3个对象，您添加了三个对象的三个引用三次。其中一个属性的变化导致所有其他属性发生变化。 它应该是有效的：

for (let i of this.myConversations) {
    this.myConversationMessage.conversationId = i.conversationId;       
    for (let j of i.messages) {
      let item = new IConversationMessages();
      item.messageId = j.messageId;
      item.messageText = j.messageText; 
      this.myConversationMessages.push(item);
    }
  }