File messages on timeline (#311)

* Create media player screen

* Introduce `FileCache` to cache message attachments

* Add file loading functionality into the media provider

* Process tap action on timeline items

* Pass item taps to view model

* Navigate to media player on view model callback

* Commit project file

* Add changelog

* Add file messages into the timeline

* Create file preview screen

* Display files in the preview screen

* Commit project file

* Update Rust SDK to 1.0.19-alpha

* Add changelog

* Bump the RustSDK to `v1.0.20-alpha`

* Configure audio session on video playback

Co-authored-by: Stefan Ceriu <stefanc@matrix.org>

ElementX/Sources/Screens/FilePreview/FilePreviewCoordinator.swift

@@ -0,0 +1,95 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import SwiftUI
+
+struct FilePreviewCoordinatorParameters {
+    let fileURL: URL
+    let title: String?
+}
+
+enum FilePreviewCoordinatorAction {
+    case cancel
+}
+
+final class FilePreviewCoordinator: Coordinator, Presentable {
+    // MARK: - Properties
+    
+    // MARK: Private
+    
+    private let parameters: FilePreviewCoordinatorParameters
+    private let filePreviewHostingController: UIViewController
+    private var filePreviewViewModel: FilePreviewViewModelProtocol
+    
+    private var indicatorPresenter: UserIndicatorTypePresenterProtocol
+    private var activityIndicator: UserIndicator?
+    
+    // MARK: Public
+
+    // Must be used only internally
+    var childCoordinators: [Coordinator] = []
+    var callback: ((FilePreviewCoordinatorAction) -> Void)?
+    
+    // MARK: - Setup
+    
+    init(parameters: FilePreviewCoordinatorParameters) {
+        self.parameters = parameters
+        
+        let viewModel = FilePreviewViewModel(fileURL: parameters.fileURL, title: parameters.title)
+        let view = FilePreviewScreen(context: viewModel.context)
+        filePreviewViewModel = viewModel
+        filePreviewHostingController = UIHostingController(rootView: view)
+        
+        indicatorPresenter = UserIndicatorTypePresenter(presentingViewController: filePreviewHostingController)
+    }
+    
+    // MARK: - Public
+    
+    func start() {
+        MXLog.debug("Did start.")
+        filePreviewViewModel.callback = { [weak self] action in
+            guard let self else { return }
+            MXLog.debug("FilePreviewViewModel did complete with result: \(action).")
+            switch action {
+            case .cancel:
+                self.callback?(.cancel)
+            }
+        }
+    }
+    
+    func toPresentable() -> UIViewController {
+        filePreviewHostingController
+    }
+
+    func stop() {
+        stopLoading()
+    }
+    
+    // MARK: - Private
+    
+    /// Show an activity indicator whilst loading.
+    /// - Parameters:
+    ///   - label: The label to show on the indicator.
+    ///   - isInteractionBlocking: Whether the indicator should block any user interaction.
+    private func startLoading(label: String = ElementL10n.loading, isInteractionBlocking: Bool = true) {
+        activityIndicator = indicatorPresenter.present(.loading(label: label, isInteractionBlocking: isInteractionBlocking))
+    }
+    
+    /// Hide the currently displayed activity indicator.
+    private func stopLoading() {
+        activityIndicator = nil
+    }
+}

ElementX/Sources/Screens/FilePreview/FilePreviewModels.swift

@@ -0,0 +1,36 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+// MARK: - Coordinator
+
+// MARK: View model
+
+enum FilePreviewViewModelAction {
+    case cancel
+}
+
+// MARK: View
+
+struct FilePreviewViewState: BindableState {
+    let fileURL: URL
+    let title: String?
+}
+
+enum FilePreviewViewAction {
+    case cancel
+}

ElementX/Sources/Screens/FilePreview/FilePreviewViewModel.swift

@@ -0,0 +1,44 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import SwiftUI
+
+typealias FilePreviewViewModelType = StateStoreViewModel<FilePreviewViewState, FilePreviewViewAction>
+
+class FilePreviewViewModel: FilePreviewViewModelType, FilePreviewViewModelProtocol {
+    // MARK: - Properties
+
+    // MARK: Private
+
+    // MARK: Public
+
+    var callback: ((FilePreviewViewModelAction) -> Void)?
+
+    // MARK: - Setup
+
+    init(fileURL: URL, title: String? = nil) {
+        super.init(initialViewState: FilePreviewViewState(fileURL: fileURL, title: title))
+    }
+    
+    // MARK: - Public
+    
+    override func process(viewAction: FilePreviewViewAction) async {
+        switch viewAction {
+        case .cancel:
+            callback?(.cancel)
+        }
+    }
+}

ElementX/Sources/Screens/FilePreview/FilePreviewViewModelProtocol.swift

@@ -0,0 +1,23 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+@MainActor
+protocol FilePreviewViewModelProtocol {
+    var callback: ((FilePreviewViewModelAction) -> Void)? { get set }
+    var context: FilePreviewViewModelType.Context { get }
+}

ElementX/Sources/Screens/FilePreview/View/FilePreviewScreen.swift

@@ -0,0 +1,95 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import QuickLook
+import SwiftUI
+import UIKit
+
+struct FilePreviewScreen: View {
+    // MARK: Private
+
+    @Environment(\.colorScheme) private var colorScheme
+    
+    var counterColor: Color {
+        colorScheme == .light ? .element.secondaryContent : .element.tertiaryContent
+    }
+    
+    // MARK: Public
+    
+    @ObservedObject var context: FilePreviewViewModel.Context
+    
+    // MARK: Views
+    
+    var body: some View {
+        PreviewController(fileURL: context.viewState.fileURL, title: context.viewState.title)
+    }
+}
+
+private struct PreviewController: UIViewControllerRepresentable {
+    let fileURL: URL
+    let title: String?
+
+    func makeUIViewController(context: Context) -> UINavigationController {
+        let controller = QLPreviewController()
+        controller.dataSource = context.coordinator
+
+        return UINavigationController(rootViewController: controller)
+    }
+
+    func updateUIViewController(_ uiViewController: UINavigationController, context: Context) { }
+
+    func makeCoordinator() -> Coordinator {
+        Coordinator(parent: self)
+    }
+
+    class Coordinator: QLPreviewControllerDataSource {
+        let parent: PreviewController
+
+        init(parent: PreviewController) {
+            self.parent = parent
+        }
+
+        func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
+            1
+        }
+
+        func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -> QLPreviewItem {
+            PreviewItem(previewItemURL: parent.fileURL, previewItemTitle: parent.title)
+        }
+    }
+}
+
+private class PreviewItem: NSObject, QLPreviewItem {
+    var previewItemURL: URL?
+    var previewItemTitle: String?
+
+    init(previewItemURL: URL?, previewItemTitle: String?) {
+        self.previewItemURL = previewItemURL
+        self.previewItemTitle = previewItemTitle
+    }
+}
+
+// MARK: - Previews
+
+struct FilePreview_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            let upgradeViewModel = FilePreviewViewModel(fileURL: URL(staticString: "https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf"))
+            FilePreviewScreen(context: upgradeViewModel.context)
+        }
+        .tint(.element.accent)
+    }
+}

ElementX/Sources/Screens/MediaPlayer/MediaPlayerCoordinator.swift

@@ -0,0 +1,94 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import SwiftUI
+
+struct MediaPlayerCoordinatorParameters {
+    let mediaURL: URL
+}
+
+enum MediaPlayerCoordinatorAction {
+    case cancel
+}
+
+final class MediaPlayerCoordinator: Coordinator, Presentable {
+    // MARK: - Properties
+    
+    // MARK: Private
+    
+    private let parameters: MediaPlayerCoordinatorParameters
+    private let mediaPlayerHostingController: UIViewController
+    private var mediaPlayerViewModel: MediaPlayerViewModelProtocol
+    
+    private var indicatorPresenter: UserIndicatorTypePresenterProtocol
+    private var activityIndicator: UserIndicator?
+    
+    // MARK: Public
+
+    // Must be used only internally
+    var childCoordinators: [Coordinator] = []
+    var callback: ((MediaPlayerCoordinatorAction) -> Void)?
+    
+    // MARK: - Setup
+    
+    init(parameters: MediaPlayerCoordinatorParameters) {
+        self.parameters = parameters
+        
+        let viewModel = MediaPlayerViewModel(mediaURL: parameters.mediaURL)
+        let view = MediaPlayerScreen(context: viewModel.context)
+        mediaPlayerViewModel = viewModel
+        mediaPlayerHostingController = UIHostingController(rootView: view)
+        
+        indicatorPresenter = UserIndicatorTypePresenter(presentingViewController: mediaPlayerHostingController)
+    }
+    
+    // MARK: - Public
+    
+    func start() {
+        MXLog.debug("Did start.")
+        mediaPlayerViewModel.callback = { [weak self] action in
+            guard let self else { return }
+            MXLog.debug("MediaPlayerViewModel did complete with result: \(action).")
+            switch action {
+            case .cancel:
+                self.callback?(.cancel)
+            }
+        }
+    }
+    
+    func toPresentable() -> UIViewController {
+        mediaPlayerHostingController
+    }
+
+    func stop() {
+        stopLoading()
+    }
+    
+    // MARK: - Private
+    
+    /// Show an activity indicator whilst loading.
+    /// - Parameters:
+    ///   - label: The label to show on the indicator.
+    ///   - isInteractionBlocking: Whether the indicator should block any user interaction.
+    private func startLoading(label: String = ElementL10n.loading, isInteractionBlocking: Bool = true) {
+        activityIndicator = indicatorPresenter.present(.loading(label: label, isInteractionBlocking: isInteractionBlocking))
+    }
+    
+    /// Hide the currently displayed activity indicator.
+    private func stopLoading() {
+        activityIndicator = nil
+    }
+}

ElementX/Sources/Screens/MediaPlayer/MediaPlayerModels.swift

@@ -0,0 +1,36 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+// MARK: - Coordinator
+
+// MARK: View model
+
+enum MediaPlayerViewModelAction {
+    case cancel
+}
+
+// MARK: View
+
+struct MediaPlayerViewState: BindableState {
+    let mediaURL: URL
+    let autoplay: Bool
+}
+
+enum MediaPlayerViewAction {
+    case cancel
+}

ElementX/Sources/Screens/MediaPlayer/MediaPlayerViewModel.swift

@@ -0,0 +1,45 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import SwiftUI
+
+typealias MediaPlayerViewModelType = StateStoreViewModel<MediaPlayerViewState, MediaPlayerViewAction>
+
+class MediaPlayerViewModel: MediaPlayerViewModelType, MediaPlayerViewModelProtocol {
+    // MARK: - Properties
+
+    // MARK: Private
+
+    // MARK: Public
+
+    var callback: ((MediaPlayerViewModelAction) -> Void)?
+
+    // MARK: - Setup
+
+    init(mediaURL: URL, autoplay: Bool = true) {
+        super.init(initialViewState: MediaPlayerViewState(mediaURL: mediaURL,
+                                                          autoplay: autoplay))
+    }
+    
+    // MARK: - Public
+    
+    override func process(viewAction: MediaPlayerViewAction) async {
+        switch viewAction {
+        case .cancel:
+            callback?(.cancel)
+        }
+    }
+}

ElementX/Sources/Screens/MediaPlayer/MediaPlayerViewModelProtocol.swift

@@ -0,0 +1,23 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+@MainActor
+protocol MediaPlayerViewModelProtocol {
+    var callback: ((MediaPlayerViewModelAction) -> Void)? { get set }
+    var context: MediaPlayerViewModelType.Context { get }
+}

ElementX/Sources/Screens/MediaPlayer/View/MediaPlayerScreen.swift

@@ -0,0 +1,52 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import AVKit
+import SwiftUI
+
+struct MediaPlayerScreen: View {
+    // MARK: Public
+    
+    @ObservedObject var context: MediaPlayerViewModel.Context
+    
+    // MARK: Views
+
+    var body: some View {
+        VideoPlayer(player: player())
+            .ignoresSafeArea()
+    }
+
+    private func player() -> AVPlayer {
+        let player = AVPlayer(url: context.viewState.mediaURL)
+        if context.viewState.autoplay {
+            player.play()
+        }
+        return player
+    }
+}
+
+// MARK: - Previews
+
+struct MediaPlayer_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            let viewModel = MediaPlayerViewModel(mediaURL: URL(staticString: "https://storage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"),
+                                                 autoplay: false)
+            MediaPlayerScreen(context: viewModel.context)
+        }
+        .tint(.element.accent)
+    }
+}

ElementX/Sources/Screens/RoomScreen/RoomScreenCoordinator.swift

@@ -65,6 +65,8 @@ final class RoomScreenCoordinator: Coordinator, Presentable {
             switch result {
             case .displayVideo(let videoURL):
                 self.displayVideo(for: videoURL)
+            case .displayFile(let fileURL, let title):
+                self.displayFile(for: fileURL, with: title)
             }
         }
     }
@@ -94,4 +96,20 @@ final class RoomScreenCoordinator: Coordinator, Presentable {
             self?.remove(childCoordinator: coordinator)
         }
     }
+
+    private func displayFile(for fileURL: URL, with title: String?) {
+        let params = FilePreviewCoordinatorParameters(fileURL: fileURL, title: title)
+        let coordinator = FilePreviewCoordinator(parameters: params)
+        coordinator.callback = { [weak self, weak coordinator] _ in
+            guard let self, let coordinator = coordinator else { return }
+            self.navigationRouter.popModule(animated: true)
+            self.remove(childCoordinator: coordinator)
+        }
+
+        add(childCoordinator: coordinator)
+        coordinator.start()
+        navigationRouter.push(coordinator) { [weak self] in
+            self?.remove(childCoordinator: coordinator)
+        }
+    }
 }

ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift

@@ -19,6 +19,7 @@ import UIKit
 
 enum RoomScreenViewModelAction {
     case displayVideo(videoURL: URL)
+    case displayFile(fileURL: URL, title: String?)
 }
 
 enum RoomScreenComposerMode: Equatable {

ElementX/Sources/Screens/RoomScreen/RoomScreenViewModel.swift

@@ -126,10 +126,11 @@ class RoomScreenViewModel: RoomScreenViewModelType, RoomScreenViewModelProtocol
         switch action {
         case .displayVideo(let videoURL):
             callback?(.displayVideo(videoURL: videoURL))
+        case .displayFile(let fileURL, let title):
+            callback?(.displayFile(fileURL: fileURL, title: title))
         case .none:
             break
         }
-
         state.showLoading = false
     }
     

ElementX/Sources/Screens/RoomScreen/View/Timeline/FileRoomTimelineView.swift

@@ -0,0 +1,81 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+import SwiftUI
+
+struct FileRoomTimelineView: View {
+    let timelineItem: FileRoomTimelineItem
+    
+    var body: some View {
+        TimelineStyler(timelineItem: timelineItem) {
+            HStack {
+                Image(systemName: "doc.text.fill")
+                    .foregroundColor(.element.primaryContent)
+                FormattedBodyText(text: timelineItem.text)
+            }
+            .padding(.vertical, 12)
+            .padding(.horizontal, 6)
+        }
+        .id(timelineItem.id)
+    }
+}
+
+struct FileRoomTimelineView_Previews: PreviewProvider {
+    static var previews: some View {
+        body.preferredColorScheme(.light)
+        body.preferredColorScheme(.dark)
+        body.preferredColorScheme(.light)
+            .timelineStyle(.plain)
+        body.preferredColorScheme(.dark)
+            .timelineStyle(.plain)
+    }
+
+    @ViewBuilder
+    static var body: some View {
+        VStack(spacing: 20.0) {
+            FileRoomTimelineView(timelineItem: FileRoomTimelineItem(id: UUID().uuidString,
+                                                                    text: "document.pdf",
+                                                                    timestamp: "Now",
+                                                                    inGroupState: .single,
+                                                                    isOutgoing: false,
+                                                                    isEditable: false,
+                                                                    senderId: "Bob",
+                                                                    source: nil,
+                                                                    thumbnailSource: nil))
+
+            FileRoomTimelineView(timelineItem: FileRoomTimelineItem(id: UUID().uuidString,
+                                                                    text: "document.docx",
+                                                                    timestamp: "Now",
+                                                                    inGroupState: .single,
+                                                                    isOutgoing: false,
+                                                                    isEditable: false,
+                                                                    senderId: "Bob",
+                                                                    source: nil,
+                                                                    thumbnailSource: nil))
+            
+            FileRoomTimelineView(timelineItem: FileRoomTimelineItem(id: UUID().uuidString,
+                                                                    text: "document.txt",
+                                                                    timestamp: "Now",
+                                                                    inGroupState: .single,
+                                                                    isOutgoing: false,
+                                                                    isEditable: false,
+                                                                    senderId: "Bob",
+                                                                    source: nil,
+                                                                    thumbnailSource: nil))
+        }
+    }
+}

ElementX/Sources/Screens/VideoPlayer/VideoPlayerCoordinator.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import AVKit
 import SwiftUI
 
 struct VideoPlayerCoordinatorParameters {
@@ -59,6 +60,9 @@ final class VideoPlayerCoordinator: Coordinator, Presentable {
     
     func start() {
         MXLog.debug("Did start.")
+
+        configureAudioSession(.sharedInstance())
+
         videoPlayerViewModel.callback = { [weak self] action in
             guard let self else { return }
             MXLog.debug("VideoPlayerViewModel did complete with result: \(action).")
@@ -78,6 +82,17 @@ final class VideoPlayerCoordinator: Coordinator, Presentable {
     }
     
     // MARK: - Private
+
+    private func configureAudioSession(_ session: AVAudioSession) {
+        do {
+            try session.setCategory(.playback,
+                                    mode: .default,
+                                    options: [.defaultToSpeaker, .allowBluetooth, .allowBluetoothA2DP])
+            try session.setActive(true)
+        } catch {
+            MXLog.debug("Configure audio session failed: \(error)")
+        }
+    }
     
     /// Show an activity indicator whilst loading.
     /// - Parameters: