Firebase Swift 3 Xcode 8 - 迭代观察结果

Question

我查看了Firebase上的文档以及Stack Overflow和YouTube教程,但是如果通过Firebase获取,我可以了解如何获取数据.

我是Firebase的新手,也是我将项目从Parse切换到Firebase的过程.

示例:我在Firebase中有一个如下所示的数据:

我可以抓住Swift中的所有主题:

 let refDB  = FIRDatabase.database().reference(fromURL: firebaseDB_URL)
    let topicsRef = refDB.child("topics")
    // FIRDataSnapshot.
    topicsRef.observe(.value, with: { snapshot in
        for child in snapshot.children {
            print("child ------")
            print(child)
            // Get the bits  HOW DO I PARSE EACH SET

        }
    })

当我遍历for循环时,我会打印出如下所示的内容:

child ------
Snap (-KYCqk2_AVkUd8s9cKit) {
    createdBy = FeMFeeDat4VZb5tmFO2tKixgQIy1;
    description = "Match states with their capitals";
    name = "State Caiptals";
    tags =     {
        0 = Geography;
        1 = USA;
    };
}

child ------
Snap (-KYCqk2_AVkUd8s9cKiu) {
    createdBy = FeMFeeDat4VZb5tmFO2tKixgQIy1;
    description = "Name the parts of an Atom";
    name = "Parts of an Antom";
    tags =     {
        0 = Physics;
        1 = Atom;
        2 = Electron;
    };
}

我的问题是,我如何获得数据:

我需要密钥(KYCqk2_AVkUd8s9cKiu)我需要描述和名称我需要一个标签数组

- 所有局部变量？

基本上,我只想读取所有内容,Topics并Topics在本地内存中有一个数组.

我可以负责构建Class主题的数组,但我已经尝试了几种方法来获取数据而没有运气.必须有一种简单的方法来解析结果,但我还没有找到示例或文档.

希望得到一些帮助或指向一些文档或教程.

=================================

更新的代码

嗨我改变了代码以尝试匹配提供的样本.代码现在看起来像下面我放入一个循环计数器,看看发生了什么以及为什么崩溃.

FDataSnapshot未定义,因此我使用了FIRDataSnapshot.

这是对现在崩溃的代码的新尝试.在下面我展示我的更改,使其不崩溃 - 以及关于安全地处理标签子节点的问题.谢谢你的指针.我现在有一些有用的东西.

// HERE is a way to get all the Topics
let refDB  = FIRDatabase.database().reference(fromURL: firebaseDB_URL)
let topicsRef = refDB.child("topics")
// FIRDataSnapshot.
topicsRef.observe(.value, with: { snapshot in

    if snapshot.value is NSNull {
        print("not found")
    } else {
        var loopCount = 1  //  count loops to see how may time trying to loop
        for child in snapshot.children {

            print("            ")
            print("            ")
            print("child ------ loop \(loopCount)")
            print(child)

            let snap = child as! FIRDataSnapshot //each child is a snapshot
            let dict = snap.value as! [String: String] // the value is a dictionary
            let name = dict["name"]!
            let description = dict["description"]!
            let createdBy = dict["createdBy"]!
            print("the bits ------")
            print("name .... \(name)")
            print("description .... \(description)")
            print("createdBy .... \(createdBy)")
            loopCount += 1

        }
    }
})

我定义了零断点 - 但是代码在此断点处停止(当我确定零断点时)

libswiftCore.dylib`_swift_bridgeNonVerbatimFromObjectiveC:
    0x1144a4270 <+0>:   pushq  %rbp
    0x1144a4271 <+1>:   movq   %rsp, %rbp
    0x1144a4274 <+4>:   pushq  %r15

...在这里打破三次,然后应用程序崩溃在这一行让dict = snap.value为![String:String],带有消息"Thread 1:EXC_BAD_INSTRUCTION(code = EXEC_1386_INVOP,subside = 0x0)

我不确定为什么代码有断点以及它崩溃的原因.可能在命中标签时崩溃,因为标签是子节点并且不适合[String,String]

我在日志中打印这个然后去繁荣!

child ------ loop 1
Snap (-KYI2MszjC9pK_4oIvKu) {
    createdBy = FeMFeeDat4VZb5tmFO2tKixgQIy1;
    description = "Match states with their capitals";
    name = "State Caiptals";
    tags =     {
        0 = Geography;
        1 = USA;
    };
}

=====

如果我改变线以使用'任何'....那么它的工作原理

let dict = snap.value as! [String: Any]

新的工作代码....

// HERE is a way to get all the Topics
let refDB  = FIRDatabase.database().reference(fromURL: firebaseDB_URL)
let topicsRef = refDB.child("topics")
// FIRDataSnapshot.
topicsRef.observe(.value, with: { snapshot in

    if snapshot.value is NSNull {
        print("not found")
    } else {
        var loopCount = 1  //  count loops to see how may time trying to loop
        for child in snapshot.children {

            print("            ")
            print("            ")
            print("child ------ loop \(loopCount)")

            let snap = child as! FIRDataSnapshot //each child is a snapshot

            if snap.value != nil {
                print("key ... \(snap.key)")
                let dict = snap.value as! [String: Any] // the value is a dictionary
                let name = dict["name"] as! String
                let description = dict["description"] as! String
                let createdBy = dict["createdBy"] as! String
                let tags = dict["tags"] as! NSArray  

                /* Thought I could loop tags as! Dictionary but that does not work. Compiles but runtime crashes.
                var tagsArray = [String]()
                if tags != nil && tags.count > 0 {
                    for (key, value) in tags {
                        tagsArray.append(value)
                    }
                } */

                // Test to see what we got ...
                print("the bits ------")
                print("name .... \(name)")
                print("description .... \(description)")
                print("createdBy .... \(createdBy)")
                print("tags ... \(tags)  ... count \(tags.count)")
                loopCount += 1
            } else {
                print("bad snap")
            }

        }
    }
})

我从其他响应发送的doc链接中找出了主题密钥.谢谢.

我不确定我是否正确获取了标签值.它实际上只是一个字典而且我试图以这种方式进行转换,但运行时崩溃并希望将标签转换为NSArray ....所以我在代码中执行了它并且它可以工作但不确定这是否安全,因为这不是定义为数组,即使它作为数组返回.

Answer 1

这真的是关于字典的.

给出一个示例节点

people_foods
  -Yinasdjasjd
     name: "Leroy"
     food: "Pizza"
  -Yk9j9s9soks
     name: "Pete"
     food: "Wings"

此代码将数据作为快照获取并迭代它以打印人员及其食物.

    let ref = self.myRootRef.child(byAppendingPath: "people_foods")!

    ref.observe(.value, with: { snapshot in

        if ( snapshot!.value is NSNull ) {
            print("not found")
        } else {

            for child in (snapshot?.children)! {

                let snap = child as! FDataSnapshot //each child is a snapshot

                let dict = snap.value as! [String: String] // the value is a dict

                let name = dict["name"]
                let food = dict["food"]

                print("\(name) loves \(food)")
            }

        }
    })

也可以使用child.key找到每个子节点的父节点名称.

典型的设计模式是利用一组类(或dicts或结构等)作为tableView的dataSource.您将遍历子项并为每个子项创建一个类,并将其附加到tableView.完成后,tableView.reloadData更新UI.

同样重要的是要记住Firebase是异步的,因此不要尝试在Observe闭包之外访问或使用该数组,直到其中的代码完成.

Answer 2

FIRDataSnapshot 的 value 属性以标准 Foundation 类型的形式返回快照的内容。