如何只显示好友的帖子？Swift / Firebase

import Firebase

// 在application(_:didFinishLaunchingWithOptions:)方法中添加以下代码
FirebaseApp.configure()

struct Post {
    let postId: String
    let userId: String
    let content: String
    // 添加其他你需要的属性
    
    init(postId: String, userId: String, content: String) {
        self.postId = postId
        self.userId = userId
        self.content = content
    }
}

import Firebase

class PostManager {
    static let shared = PostManager()
    private let databaseRef = Database.database().reference()
    
    func getFriendPosts(friendId: String, completion: @escaping ([Post]) -> Void) {
        databaseRef.child("posts").child(friendId).observeSingleEvent(of: .value) { (snapshot) in
            var posts: [Post] = []
            for child in snapshot.children {
                if let childSnapshot = child as? DataSnapshot,
                   let postDict = childSnapshot.value as? [String: Any],
                   let postId = postDict["postId"] as? String,
                   let userId = postDict["userId"] as? String,
                   let content = postDict["content"] as? String {
                    let post = Post(postId: postId, userId: userId, content: content)
                    posts.append(post)
                }
            }
            completion(posts)
        }
    }
}

import UIKit

class ViewController: UIViewController {
    var friendPosts: [Post] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let friendId = "好友的用户ID"
        PostManager.shared.getFriendPosts(friendId: friendId) { [weak self] (posts) in
            self?.friendPosts = posts
            // 更新界面显示
        }
    }
}