angular - 如何检查多条件以将 observable 与 rxjs 连接起来

Question

我想对可观察到的消息进行检查，并像这样场景化输出:检查消息是发给我的还是发 self 的，并将前 20 个字符与 friend 的名字 连接起来，或者是我与你 的消息如果是照片或文件，请检查消息的类型，例如发送一条消息

getLastMessage(onlineUserModel: OnlineUserModel): Observable<string> {
    let message: Observable<string>;
   
    const messageModel = this.allDirectMessages$
      .pipe(
        map((x) =>
          x.filter(
            (f) =>
              f.messageModel.to.userName === onlineUserModel.userName ||
              f.messageModel.from.userName === onlineUserModel.userName
          )
        )
      )
      .pipe(map((data) => data[data.length - 1].messageModel))
      .pipe(
        map((item) => {
          if (item.to.userName == onlineUserModel.userName) {
            message = concat("You", item.content, "...");
          }
          else (item.to.userName == onlineUserModel.userName) {
            message = concat("You", item.content, "...");
          }
        })
      );

   
    return message;
  }

Answer 1

如果您想将消息作为 Observable<string> 返回你可以这样做:

getLastMessage(onlineUserModel: OnlineUserModel): Observable<string> {   
  return this.allDirectMessages$
    .pipe(
      filter((f) =>
          f.messageModel.to.userName === onlineUserModel.userName ||
          f.messageModel.from.userName === onlineUserModel.userName
      ),
      map((data) => {
        const item = data[data.length - 1].messageModel;
        if (item.to.userName == onlineUserModel.userName) {
          return `You ${item.content}...`;
        }
        else (item.from.userName == onlineUserModel.userName) {
          return `Them ${item.content}...`;
        }
      })
    );
}