如何在 ngFor 中使用嵌套 json 对象

Question

我在遍历 json 对象以显示消息时遇到问题。场景是我将 from_id 发送到 to_id 的消息和 jsonData 如下：

jsonData={
    "chat":
    {
        "79":
        {
            "from":"Testing Page - joe",
            "from_id":79,
            "to":"userTestName",
            "to_id":1548,
            "unread":2,
            "messages":
            [
                {"id":154,"page_id":79,"user_id":1548,"text":"this is the first message to be sent by joe","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-10 13:54:10","updated_at":"2019-04-10 13:54:10"},
                {"id":155,"page_id":79,"user_id":1548,"text":"this is the second message sent to joe","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-11 12:37:39","updated_at":"2019-04-11 12:37:39"}
            ]
        },
        "44":
        {
            "from":"Rock Music Band",
            "from_id":44,
            "to":"userTestName",
            "to_id":1548,
            "unread":1,
            "messages":
            [
                {"id":156,"page_id":44,"user_id":1548,"text":"Hello this message from rock","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-11 13:18:44","updated_at":"2019-04-11 13:18:44"}
            ]
        }
    },
    "unread":3
}

我在使用 angular *ngFor:

在 <ul> 中显示这些消息时遇到问题

  <ul>
    <li *ngFor="let messageData of jsonData.chat;>
      <div class="message-info">
        <h4>{{messageData.from}}</h4>
        <h4>{{messageData.messages[0].text}}</h4>
      </div>
    </li>
  </ul>

我收到不支持对象的错误消息。

ERROR Error: Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays.

我的 json数据应该是什么样子才能显示消息？我希望每个 id 79 - ‘44’ 是一个单独的对象。

Answer 1

jsonData 是对象而不是数组，因此出错。您可能想使用 KeyValuePipe:

<ul>
  <li *ngFor="let data of jsonData.chat | keyvalue>
    <div class="message-info">
      <h4>{{jsonData.chat[data.key].from}}</h4> <!-- Or even better: data.value.from -->
      <h4>{{jsonData.chat[data.key].messages[0].text}}</h4> <!-- Or even better: data.value.messages[0].text -->
      <!-- Want to loop through your messages? -->
      <ul>
        <li *ngFor="let message of data.value.messages">{{message.text}}</li>
      </ul>
    </div>
  </li>
</ul>

尽管将数据转换为数组可能是值得的。

Answer 2

您必须将 json 格式化为数组，以便 ngFor 工作，我认为这就是您要找的东西： https://stackblitz.com/edit/angular-h7ezpn?file=src%2Fapp%2Fapp.component.ts

  "chat":
  [
      {"title" :"79",
      "content":
      {
          "from":"Testing Page - joe",
          "from_id":79,
          "to":"userTestName",
          "to_id":1548,
          "unread":2,
          "messages":
          [
              {"id":154,"page_id":79,"user_id":1548,"text":"this is the first message to be sent by joe","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-10 13:54:10","updated_at":"2019-04-10 13:54:10"},
              {"id":155,"page_id":79,"user_id":1548,"text":"this is the second message sent to joe","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-11 12:37:39","updated_at":"2019-04-11 12:37:39"}
          ]
      }},
      {
       "title" :"44",
       "content":
      {
          "from":"Rock Music Band",
          "from_id":44,
          "to":"userTestName",
          "to_id":1548,
          "unread":1,
          "messages":
          [
              {"id":156,"page_id":44,"user_id":1548,"text":"Hello this message from rock","seen":0,"isgroup":0,"group_id":null,"created_at":"2019-04-11 13:18:44","updated_at":"2019-04-11 13:18:44"}
          ]
      }}
  ],
  "unread":3
}

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