# 使用 IVS iOS 廣播 SDK 發布和訂閱
<a name="getting-started-pub-sub-ios"></a>

本節將引導您完成使用 iOS 應用程式發布和訂閱階段的相關步驟。

## 建立檢視
<a name="getting-started-pub-sub-ios-views"></a>

首先，使用自動建立用於匯入 `AmazonIVSBroadcast` 的 `ViewController.swift` 檔案，然後新增一些要連結的 `@IBOutlets`：

```
import AmazonIVSBroadcast

class ViewController: UIViewController {

    @IBOutlet private var textFieldToken: UITextField!
    @IBOutlet private var buttonJoin: UIButton!
    @IBOutlet private var labelState: UILabel!
    @IBOutlet private var switchPublish: UISwitch!
    @IBOutlet private var collectionViewParticipants: UICollectionView!
```

現在，建立這些檢視，並在 `Main.storyboard` 中將其連結。以下是將使用的檢視結構：

![\[使用 Main.storyboard 來建立 iOS 檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_1.png)


若是 AutoLayout 組態，需要自訂三個檢視。第一個檢視是**集合檢視參與者** (`UICollectionView`)。將**前導**、**尾隨**和**底部**繫結至**安全區域**。同時將**頂部**繫結至**控制容器**。

![\[自訂 iOS 集合檢視參與者的檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_2.png)


第二個檢視是**控制容器**。將**前導**、**尾隨**和**頂部**繫結至**安全區域**。

![\[自訂 iOS 控制容器檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_3.png)


第三個和最後一個檢視是**垂直堆疊檢視**。將**頂部**、**前導**、**尾隨**和**底部**繫結至**父檢視**。針對樣式，將間距設定為 8，而不是 0。

![\[自訂 iOS 垂直堆疊檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_4.png)


**UIStackViews** 會處理其餘檢視的配置。針對所有三個 **UIStackViews**，在**對齊**和**分佈**時使用**填滿**。

![\[使用 UIStackViews 自訂其餘的 iOS 檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_5.png)


最後，將這些檢視連結至 `ViewController`。從上方映射下列檢視：
+ **文字欄位加入**繫結至 `textFieldToken`。
+ **按鈕加入**繫結至 `buttonJoin`。
+ **標籤狀態**繫結至 `labelState`。
+ **切換發布**繫結至 `switchPublish`。
+ **集合檢視參與者**繫結至 `collectionViewParticipants`。

同時還會將**集合檢視參與者**項目的 `dataSource` 設定為擁有的 `ViewController`:

![\[若是 iOS 應用程式，還會設定集合檢視參與者的資料來源。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_6.png)


現在，建立要在其中轉譯參與者的 `UICollectionViewCell` 子類別。首先，建立一個新的 **Cocoa Touch 類別**檔案：

![\[建立 UICollectionViewCell，以轉譯 iOS 即時參與者。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_7.png)


將其命名為 `ParticipantUICollectionViewCell`，然後使其成為 Swift 中 `UICollectionViewCell` 的子類別。再次從 Swift 檔案開始，建立要連結的 `@IBOutlets`：

```
import AmazonIVSBroadcast

class ParticipantCollectionViewCell: UICollectionViewCell {

    @IBOutlet private var viewPreviewContainer: UIView!
    @IBOutlet private var labelParticipantId: UILabel!
    @IBOutlet private var labelSubscribeState: UILabel!
    @IBOutlet private var labelPublishState: UILabel!
    @IBOutlet private var labelVideoMuted: UILabel!
    @IBOutlet private var labelAudioMuted: UILabel!
    @IBOutlet private var labelAudioVolume: UILabel!
```

在關聯的 XIB 檔案中，建立此檢視階層：

![\[在關聯的 XIB 檔案中，建立 iOS 檢視階層。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_8.png)


針對 AutoLayout，將再次修改三個檢視。第一個檢視是**檢視預覽容器**。將**尾隨**、**前導**、**頂部**和**底部**設定為**參與者集合檢視儲存格**。

![\[自訂 iOS 檢視預覽容器檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_9.png)


第二個檢視是**檢視**。將**前導**和**頂部**設定為**參與者集合檢視儲存格**，並將該值變更為 4。

![\[自訂 iOS 檢視的檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_10.png)


第三個檢視是**堆疊檢視**。將 **Trailing**、**Leading**、**Top** 和 **Bottom** 設定為 **Superview**，並將值變更為 4。

![\[自訂 iOS 堆疊檢視的檢視。\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_11.png)


## 許可和閒置計時器
<a name="getting-started-pub-sub-ios-perms"></a>

回到 `ViewController`，將停用系統閒置計時器，以免在使用應用程式時，裝置進入睡眠狀態：

```
override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    // Prevent the screen from turning off during a call.
    UIApplication.shared.isIdleTimerDisabled = true
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    UIApplication.shared.isIdleTimerDisabled = false
}
```

接著，請求系統的攝影機和麥克風許可：

```
private func checkPermissions() {
    checkOrGetPermission(for: .video) { [weak self] granted in
        guard granted else {
            print("Video permission denied")
            return
        }
        self?.checkOrGetPermission(for: .audio) { [weak self] granted in
            guard granted else {
                print("Audio permission denied")
                return
            }
            self?.setupLocalUser() // we will cover this later
        }
    }
}

private func checkOrGetPermission(for mediaType: AVMediaType, _ result: @escaping (Bool) -> Void) {
    func mainThreadResult(_ success: Bool) {
        DispatchQueue.main.async {
            result(success)
        }
    }
    switch AVCaptureDevice.authorizationStatus(for: mediaType) {
    case .authorized: mainThreadResult(true)
    case .notDetermined:
        AVCaptureDevice.requestAccess(for: mediaType) { granted in
            mainThreadResult(granted)
        }
    case .denied, .restricted: mainThreadResult(false)
    @unknown default: mainThreadResult(false)
    }
}
```

## 應用程式狀態
<a name="getting-started-pub-sub-ios-app-state"></a>

需要設定 `collectionViewParticipants` 以及之前建立的配置檔案：

```
override func viewDidLoad() {
    super.viewDidLoad()
    // We render everything to exactly the frame, so don't allow scrolling.
    collectionViewParticipants.isScrollEnabled = false
    collectionViewParticipants.register(UINib(nibName: "ParticipantCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: "ParticipantCollectionViewCell")
}
```

為了代表每個參與者，我們建立了一個稱為 `StageParticipant` 的簡單結構。這可包含在 `ViewController.swift` 檔案中，或建立新的檔案。

```
import Foundation
import AmazonIVSBroadcast

struct StageParticipant {
    let isLocal: Bool
    var participantId: String?
    var publishState: IVSParticipantPublishState = .notPublished
    var subscribeState: IVSParticipantSubscribeState = .notSubscribed
    var streams: [IVSStageStream] = []

    init(isLocal: Bool, participantId: String?) {
        self.isLocal = isLocal
        self.participantId = participantId
    }
}
```

為了追蹤這些參與者，我們將其陣列做為私有屬性保留在 `ViewController` 中:

```
private var participants = [StageParticipant]()
```

此屬性將用於支援之前從分鏡腳本連結的 `UICollectionViewDataSource`：

```
extension ViewController: UICollectionViewDataSource {

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return participants.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ParticipantCollectionViewCell", for: indexPath) as? ParticipantCollectionViewCell {
            cell.set(participant: participants[indexPath.row])
            return cell
        } else {
            fatalError("Couldn't load custom cell type 'ParticipantCollectionViewCell'")
        }
    }

}
```

若要在加入階段之前查看您自己的預覽，我們會立即建立本機參與者：

```
override func viewDidLoad() {
    /* existing UICollectionView code */
    participants.append(StageParticipant(isLocal: true, participantId: nil))
}
```

這會導致在應用程式執行後，代表本機參與者立即轉譯參與者儲存格。

使用者希望能夠在加入階段之前看到自己，因此，接下來我們實作 `setupLocalUser()` 方法，可從稍早的許可處理程式碼中呼叫。將攝影機和麥克風參考做為 `IVSLocalStageStream` 物件來存放。

```
private var streams = [IVSLocalStageStream]()
private let deviceDiscovery = IVSDeviceDiscovery()

private func setupLocalUser() {
    // Gather our camera and microphone once permissions have been granted
    let devices = deviceDiscovery.listLocalDevices()
    streams.removeAll()
    if let camera = devices.compactMap({ $0 as? IVSCamera }).first {
        streams.append(IVSLocalStageStream(device: camera))
        // Use a front camera if available.
        if let frontSource = camera.listAvailableInputSources().first(where: { $0.position == .front }) {
            camera.setPreferredInputSource(frontSource)
        }
    }
    if let mic = devices.compactMap({ $0 as? IVSMicrophone }).first {
        streams.append(IVSLocalStageStream(device: mic))
    }
    participants[0].streams = streams
    participantsChanged(index: 0, changeType: .updated)
}
```

在這裡透過 SDK 找到了裝置的攝影機和麥克風，並將其存放在本機 `streams` 物件中，然後將第一個參與者 (我們之前建立的本機參與者) 的 `streams` 陣列指派到 `streams`。最後，呼叫 `index` 為 0，以及 `changeType` 為 `updated` 的 `participantsChanged`。該函數是透過良好的動畫更新 `UICollectionView` 的輔助程式函數。這是呈現的外觀：

```
private func participantsChanged(index: Int, changeType: ChangeType) {
    switch changeType {
    case .joined:
        collectionViewParticipants?.insertItems(at: [IndexPath(item: index, section: 0)])
    case .updated:
        // Instead of doing reloadItems, just grab the cell and update it ourselves. It saves a create/destroy of a cell
        // and more importantly fixes some UI flicker. We disable scrolling so the index path per cell
        // never changes.
        if let cell = collectionViewParticipants?.cellForItem(at: IndexPath(item: index, section: 0)) as? ParticipantCollectionViewCell {
            cell.set(participant: participants[index])
        }
    case .left:
        collectionViewParticipants?.deleteItems(at: [IndexPath(item: index, section: 0)])
    }
}
```

別擔心 `cell.set`；稍後會處理，這就是我們將根據參與者轉譯儲存格內容的地方。

`ChangeType` 是一個簡單的列舉：

```
enum ChangeType {
    case joined, updated, left
}
```

最後，想要追蹤階段是否已建立連線。使用一個簡單的 `bool` 來追蹤，在其自行更新時，會自動更新 UI。

```
private var connectingOrConnected = false {
    didSet {
        buttonJoin.setTitle(connectingOrConnected ? "Leave" : "Join", for: .normal)
        buttonJoin.tintColor = connectingOrConnected ? .systemRed : .systemBlue
    }
}
```

## 實作階段 SDK
<a name="getting-started-pub-sub-ios-stage-sdk"></a>

以下是三個以即時功能為基礎的核心[概念](ios-publish-subscribe.md#ios-publish-subscribe-concepts)：階段、策略和轉譯器。設計目標是盡可能減少打造工作產品所需的用戶端邏輯數量。

### IVSStageStrategy
<a name="getting-started-pub-sub-ios-stage-sdk-strategy"></a>

`IVSStageStrategy` 實作很簡單：

```
extension ViewController: IVSStageStrategy {
    func stage(_ stage: IVSStage, streamsToPublishForParticipant participant: IVSParticipantInfo) -> [IVSLocalStageStream] {
        // Return the camera and microphone to be published.
        // This is only called if `shouldPublishParticipant` returns true.
        return streams
    }

    func stage(_ stage: IVSStage, shouldPublishParticipant participant: IVSParticipantInfo) -> Bool {
        // Our publish status is based directly on the UISwitch view
        return switchPublish.isOn
    }

    func stage(_ stage: IVSStage, shouldSubscribeToParticipant participant: IVSParticipantInfo) -> IVSStageSubscribeType {
        // Subscribe to both audio and video for all publishing participants.
        return .audioVideo
    }
}
```

總而言之，只有在發布切換按鈕處於「開啟」位置時才會發布，如果要發布，我們會發布之前收集的串流。最後，針對此範例，始終會訂閱其他參與者，同時接收其音訊和影片。

### IVSStageRenderer
<a name="getting-started-pub-sub-ios-stage-sdk-renderer"></a>

`IVSStageRenderer` 實作也非常簡單，但要考慮包含相當多程式碼的函數數量。當 SDK 通知我們有關參與者的變更時，此轉譯器中的一般方法是更新我們的 `participants` 陣列。在某些情況下，對於本機參與者的處理方式有所不同，因為我們已決定自行管理他們，以便在他們加入之前查看其攝影機預覽。

```
extension ViewController: IVSStageRenderer {

    func stage(_ stage: IVSStage, didChange connectionState: IVSStageConnectionState, withError error: Error?) {
        labelState.text = connectionState.text
        connectingOrConnected = connectionState != .disconnected
    }

    func stage(_ stage: IVSStage, participantDidJoin participant: IVSParticipantInfo) {
        if participant.isLocal {
            // If this is the local participant joining the Stage, update the first participant in our array because we
            // manually added that participant when setting up our preview
            participants[0].participantId = participant.participantId
            participantsChanged(index: 0, changeType: .updated)
        } else {
            // If they are not local, add them to the array as a newly joined participant.
            participants.append(StageParticipant(isLocal: false, participantId: participant.participantId))
            participantsChanged(index: (participants.count - 1), changeType: .joined)
        }
    }

    func stage(_ stage: IVSStage, participantDidLeave participant: IVSParticipantInfo) {
        if participant.isLocal {
            // If this is the local participant leaving the Stage, update the first participant in our array because
            // we want to keep the camera preview active
            participants[0].participantId = nil
            participantsChanged(index: 0, changeType: .updated)
        } else {
            // If they are not local, find their index and remove them from the array.
            if let index = participants.firstIndex(where: { $0.participantId == participant.participantId }) {
                participants.remove(at: index)
                participantsChanged(index: index, changeType: .left)
            }
        }
    }

    func stage(_ stage: IVSStage, participant: IVSParticipantInfo, didChange publishState: IVSParticipantPublishState) {
        // Update the publishing state of this participant
        mutatingParticipant(participant.participantId) { data in
            data.publishState = publishState
        }
    }

    func stage(_ stage: IVSStage, participant: IVSParticipantInfo, didChange subscribeState: IVSParticipantSubscribeState) {
        // Update the subscribe state of this participant
        mutatingParticipant(participant.participantId) { data in
            data.subscribeState = subscribeState
        }
    }

    func stage(_ stage: IVSStage, participant: IVSParticipantInfo, didChangeMutedStreams streams: [IVSStageStream]) {
        // We don't want to take any action for the local participant because we track those streams locally
        if participant.isLocal { return }
        // For remote participants, notify the UICollectionView that they have updated. There is no need to modify
        // the `streams` property on the `StageParticipant` because it is the same `IVSStageStream` instance. Just
        // query the `isMuted` property again.
        if let index = participants.firstIndex(where: { $0.participantId == participant.participantId }) {
            participantsChanged(index: index, changeType: .updated)
        }
    }

    func stage(_ stage: IVSStage, participant: IVSParticipantInfo, didAdd streams: [IVSStageStream]) {
        // We don't want to take any action for the local participant because we track those streams locally
        if participant.isLocal { return }
        // For remote participants, add these new streams to that participant's streams array.
        mutatingParticipant(participant.participantId) { data in
            data.streams.append(contentsOf: streams)
        }
    }

    func stage(_ stage: IVSStage, participant: IVSParticipantInfo, didRemove streams: [IVSStageStream]) {
        // We don't want to take any action for the local participant because we track those streams locally
        if participant.isLocal { return }
        // For remote participants, remove these streams from that participant's streams array.
        mutatingParticipant(participant.participantId) { data in
            let oldUrns = streams.map { $0.device.descriptor().urn }
            data.streams.removeAll(where: { stream in
                return oldUrns.contains(stream.device.descriptor().urn)
            })
        }
    }

    // A helper function to find a participant by its ID, mutate that participant, and then update the UICollectionView accordingly.
    private func mutatingParticipant(_ participantId: String?, modifier: (inout StageParticipant) -> Void) {
        guard let index = participants.firstIndex(where: { $0.participantId == participantId }) else {
            fatalError("Something is out of sync, investigate if this was a sample app or SDK issue.")
        }

        var participant = participants[index]
        modifier(&participant)
        participants[index] = participant
        participantsChanged(index: index, changeType: .updated)
    }
}
```

此程式碼使用延伸，將連線狀態轉換為易讀的文字：

```
extension IVSStageConnectionState {
    var text: String {
        switch self {
        case .disconnected: return "Disconnected"
        case .connecting: return "Connecting"
        case .connected: return "Connected"
        @unknown default: fatalError()
        }
    }
}
```

## 實作自訂 UICollectionViewLayout
<a name="getting-started-pub-sub-ios-layout"></a>

配置不同數量的參與者可能很複雜。您希望他們佔用整個父檢視的框架，但不想單獨處理每個參與者配置。為了簡化這一點，我們將逐步實作 `UICollectionViewLayout`。

建立另一個新檔案 `ParticipantCollectionViewLayout.swift`，這應當會延伸 `UICollectionViewLayout`。此類別會使用另一個稱為 `StageLayoutCalculator` 類別，我們很快會介紹。該類別會接收針對每個參與者計算的影格值，然後產生必要的 `UICollectionViewLayoutAttributes` 物件。

```
import Foundation
import UIKit

/**
 Code modified from https://developer.apple.com/documentation/uikit/views_and_controls/collection_views/layouts/customizing_collection_view_layouts?language=objc
 */
class ParticipantCollectionViewLayout: UICollectionViewLayout {

    private let layoutCalculator = StageLayoutCalculator()

    private var contentBounds = CGRect.zero
    private var cachedAttributes = [UICollectionViewLayoutAttributes]()

    override func prepare() {
        super.prepare()

        guard let collectionView = collectionView else { return }

        cachedAttributes.removeAll()
        contentBounds = CGRect(origin: .zero, size: collectionView.bounds.size)

        layoutCalculator.calculateFrames(participantCount: collectionView.numberOfItems(inSection: 0),
                                         width: collectionView.bounds.size.width,
                                         height: collectionView.bounds.size.height,
                                         padding: 4)
        .enumerated()
        .forEach { (index, frame) in
            let attributes = UICollectionViewLayoutAttributes(forCellWith: IndexPath(item: index, section: 0))
            attributes.frame = frame
            cachedAttributes.append(attributes)
            contentBounds = contentBounds.union(frame)
        }
    }

    override var collectionViewContentSize: CGSize {
        return contentBounds.size
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        guard let collectionView = collectionView else { return false }
        return !newBounds.size.equalTo(collectionView.bounds.size)
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return cachedAttributes[indexPath.item]
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var attributesArray = [UICollectionViewLayoutAttributes]()

        // Find any cell that sits within the query rect.
        guard let lastIndex = cachedAttributes.indices.last, let firstMatchIndex = binSearch(rect, start: 0, end: lastIndex) else {
            return attributesArray
        }

        // Starting from the match, loop up and down through the array until all the attributes
        // have been added within the query rect.
        for attributes in cachedAttributes[..<firstMatchIndex].reversed() {
            guard attributes.frame.maxY >= rect.minY else { break }
            attributesArray.append(attributes)
        }

        for attributes in cachedAttributes[firstMatchIndex...] {
            guard attributes.frame.minY <= rect.maxY else { break }
            attributesArray.append(attributes)
        }

        return attributesArray
    }

    // Perform a binary search on the cached attributes array.
    func binSearch(_ rect: CGRect, start: Int, end: Int) -> Int? {
        if end < start { return nil }

        let mid = (start + end) / 2
        let attr = cachedAttributes[mid]

        if attr.frame.intersects(rect) {
            return mid
        } else {
            if attr.frame.maxY < rect.minY {
                return binSearch(rect, start: (mid + 1), end: end)
            } else {
                return binSearch(rect, start: start, end: (mid - 1))
            }
        }
    }
}
```

更重要的是 `StageLayoutCalculator.swift` 類別。設計此類別的目的是，根據以流程為基礎的資料列/資料欄配置中的參與者人數，來計算每個參與者的影格。每個資料列的高度與其他資料列相同，但每個資料列的寬度可能有所差異。請參閱 `layouts` 變數上方的程式碼註解，描述了如何自訂此行為。

```
import Foundation
import UIKit

class StageLayoutCalculator {

    /// This 2D array contains the description of how the grid of participants should be rendered
    /// The index of the 1st dimension is the number of participants needed to active that configuration
    /// Meaning if there is 1 participant, index 0 will be used. If there are 5 participants, index 4 will be used.
    ///
    /// The 2nd dimension is a description of the layout. The length of the array is the number of rows that
    /// will exist, and then each number within that array is the number of columns in each row.
    ///
    /// See the code comments next to each index for concrete examples.
    ///
    /// This can be customized to fit any layout configuration needed.
    private let layouts: [[Int]] = [
        // 1 participant
        [ 1 ], // 1 row, full width
        // 2 participants
        [ 1, 1 ], // 2 rows, all columns are full width
        // 3 participants
        [ 1, 2 ], // 2 rows, first row's column is full width then 2nd row's columns are 1/2 width
        // 4 participants
        [ 2, 2 ], // 2 rows, all columns are 1/2 width
        // 5 participants
        [ 1, 2, 2 ], // 3 rows, first row's column is full width, 2nd and 3rd row's columns are 1/2 width
        // 6 participants
        [ 2, 2, 2 ], // 3 rows, all column are 1/2 width
        // 7 participants
        [ 2, 2, 3 ], // 3 rows, 1st and 2nd row's columns are 1/2 width, 3rd row's columns are 1/3rd width
        // 8 participants
        [ 2, 3, 3 ],
        // 9 participants
        [ 3, 3, 3 ],
        // 10 participants
        [ 2, 3, 2, 3 ],
        // 11 participants
        [ 2, 3, 3, 3 ],
        // 12 participants
        [ 3, 3, 3, 3 ],
    ]

    // Given a frame (this could be for a UICollectionView, or a Broadcast Mixer's canvas), calculate the frames for each
    // participant, with optional padding.
    func calculateFrames(participantCount: Int, width: CGFloat, height: CGFloat, padding: CGFloat) -> [CGRect] {
        if participantCount > layouts.count {
            fatalError("Only \(layouts.count) participants are supported at this time")
        }
        if participantCount == 0 {
            return []
        }
        var currentIndex = 0
        var lastFrame: CGRect = .zero

        // If the height is less than the width, the rows and columns will be flipped.
        // Meaning for 6 participants, there will be 2 rows of 3 columns each.
        let isVertical = height > width

        let halfPadding = padding / 2.0

        let layout = layouts[participantCount - 1] // 1 participant is in index 0, so `-1`.
        let rowHeight = (isVertical ? height : width) / CGFloat(layout.count)

        var frames = [CGRect]()
        for row in 0 ..< layout.count {
            // layout[row] is the number of columns in a layout
            let itemWidth = (isVertical ? width : height) / CGFloat(layout[row])
            let segmentFrame = CGRect(x: (isVertical ? 0 : lastFrame.maxX) + halfPadding,
                                      y: (isVertical ? lastFrame.maxY : 0) + halfPadding,
                                      width: (isVertical ? itemWidth : rowHeight) - padding,
                                      height: (isVertical ? rowHeight : itemWidth) - padding)

            for column in 0 ..< layout[row] {
                var frame = segmentFrame
                if isVertical {
                    frame.origin.x = (itemWidth * CGFloat(column)) + halfPadding
                } else {
                    frame.origin.y = (itemWidth * CGFloat(column)) + halfPadding
                }
                frames.append(frame)
                currentIndex += 1
            }

            lastFrame = segmentFrame
            lastFrame.origin.x += halfPadding
            lastFrame.origin.y += halfPadding
        }
        return frames
    }

}
```

回到 `Main.storyboard`，請務必將 `UICollectionView` 的配置類別設定為我們剛才建立的類別：

![\[Xcode interface showing storyboard with UICollectionView and its layout settings.\]](http://docs.aws.amazon.com/zh_tw/ivs/latest/RealTimeUserGuide/images/Publish_iOS_12.png)


## 掛接 UI 動作
<a name="getting-started-pub-sub-ios-actions"></a>

我們即將結束，只需建立幾個 `IBActions`。

首先，將處理加入按鈕。其反應因 `connectingOrConnected` 的值而異。一旦建立連線後，便會離開階段。如果中斷連線，則會從權杖 `UITextField` 讀取文字，並建立具有該文字的新的 `IVSStage`。然後，新增 `ViewController` 做為 `strategy`、`errorDelegate` 和用於 `IVSStage` 的轉譯器，最後，我們以非同步方式加入階段。

```
@IBAction private func joinTapped(_ sender: UIButton) {
    if connectingOrConnected {
        // If we're already connected to a Stage, leave it.
        stage?.leave()
    } else {
        guard let token = textFieldToken.text else {
            print("No token")
            return
        }
        // Hide the keyboard after tapping Join
        textFieldToken.resignFirstResponder()
        do {
            // Destroy the old Stage first before creating a new one.
            self.stage = nil
            let stage = try IVSStage(token: token, strategy: self)
            stage.errorDelegate = self
            stage.addRenderer(self)
            try stage.join()
            self.stage = stage
        } catch {
            print("Failed to join stage - \(error)")
        }
    }
}
```

需要掛接的另一個 UI 動作是發布切換按鈕：

```
@IBAction private func publishToggled(_ sender: UISwitch) {
    // Because the strategy returns the value of `switchPublish.isOn`, just call `refreshStrategy`.
    stage?.refreshStrategy()
}
```

## 轉譯參與者
<a name="getting-started-pub-sub-ios-participants"></a>

最後，我們需要將從 SDK 接收的資料，轉譯到之前建立的參與者儲存格上。我們已經完成了 `UICollectionView` 邏輯，因此只需實作 `ParticipantCollectionViewCell.swift` 中的 `set` API。

從新增 `empty` 函數開始，然後逐步實作：

```
func set(participant: StageParticipant) {
   
}
```

首先，處理簡易狀態、參與者 ID、發布狀態和訂閱狀態。對於這些，只需直接更新 `UILabels`：

```
labelParticipantId.text = participant.isLocal ? "You (\(participant.participantId ?? "Disconnected"))" : participant.participantId
labelPublishState.text = participant.publishState.text
labelSubscribeState.text = participant.subscribeState.text
```

發布和訂閱列舉的文字屬性源自本機延伸：

```
extension IVSParticipantPublishState {
    var text: String {
        switch self {
        case .notPublished: return "Not Published"
        case .attemptingPublish: return "Attempting to Publish"
        case .published: return "Published"
        @unknown default: fatalError()
        }
    }
}

extension IVSParticipantSubscribeState {
    var text: String {
        switch self {
        case .notSubscribed: return "Not Subscribed"
        case .attemptingSubscribe: return "Attempting to Subscribe"
        case .subscribed: return "Subscribed"
        @unknown default: fatalError()
        }
    }
}
```

接著，更新音訊和影片靜音狀態。為取得靜音狀態，需要從 `streams` 陣列中找到 `IVSImageDevice` 和 `IVSAudioDevice`。為優化效能，會記住上次連接的裝置。

```
// This belongs outside `set(participant:)`
private var registeredStreams: Set<IVSStageStream> = []
private var imageDevice: IVSImageDevice? {
    return registeredStreams.lazy.compactMap { $0.device as? IVSImageDevice }.first
}
private var audioDevice: IVSAudioDevice? {
    return registeredStreams.lazy.compactMap { $0.device as? IVSAudioDevice }.first
}

// This belongs inside `set(participant:)`
let existingAudioStream = registeredStreams.first { $0.device is IVSAudioDevice }
let existingImageStream = registeredStreams.first { $0.device is IVSImageDevice }

registeredStreams = Set(participant.streams)

let newAudioStream = participant.streams.first { $0.device is IVSAudioDevice }
let newImageStream = participant.streams.first { $0.device is IVSImageDevice }

// `isMuted != false` covers the stream not existing, as well as being muted.
labelVideoMuted.text = "Video Muted: \(newImageStream?.isMuted != false)"
labelAudioMuted.text = "Audio Muted: \(newAudioStream?.isMuted != false)"
```

最後，要轉譯 `imageDevice` 的預覽，並顯示 `audioDevice` 的音訊統計資料:

```
if existingImageStream !== newImageStream {
    // The image stream has changed
    updatePreview() // We’ll cover this next
}

if existingAudioStream !== newAudioStream {
    (existingAudioStream?.device as? IVSAudioDevice)?.setStatsCallback(nil)
    audioDevice?.setStatsCallback( { [weak self] stats in
        self?.labelAudioVolume.text = String(format: "Audio Level: %.0f dB", stats.rms)
    })
    // When the audio stream changes, it will take some time to receive new stats. Reset the value temporarily.
    self.labelAudioVolume.text = "Audio Level: -100 dB"
}
```

我們需要建立的最後一個函數是 `updatePreview()`，這會將參與者的預覽新增至檢視：

```
private func updatePreview() {
    // Remove any old previews from the preview container
    viewPreviewContainer.subviews.forEach { $0.removeFromSuperview() }
    if let imageDevice = self.imageDevice {
        if let preview = try? imageDevice.previewView(with: .fit) {
            viewPreviewContainer.addSubviewMatchFrame(preview)
        }
    }
}
```

上面使用了 `UIView` 上的輔助程式函數，使嵌入子檢視變得更容易：

```
extension UIView {
    func addSubviewMatchFrame(_ view: UIView) {
        view.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(view)
        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: self.topAnchor, constant: 0),
            view.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: 0),
            view.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 0),
            view.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: 0),
        ])
    }
}
```