完善直播消息滚动机制

src/App/Controls/Player/BiliPlayerTransportControls/BiliPlayerTransportControls.xaml

@@ -1057,7 +1057,7 @@
                                     <Grid
                                         x:Name="Danmaku_Command_Border"
                                         Grid.Row="1"
-                                        Padding="4"
+                                        Padding="4,4,8,4"
                                         BorderBrush="{ThemeResource ControlStrokeColorDefaultBrush}"
                                         BorderThickness="0,1,0,0">
                                         <local:DanmakuBox />

src/App/Controls/Player/Related/LiveMessageView.xaml

@@ -36,6 +36,7 @@
         <ScrollViewer
             x:Name="ScrollViewer"
             HorizontalScrollMode="Disabled"
+            ViewChanged="OnViewChanged"
             VerticalScrollBarVisibility="Auto">
             <Grid>
                 <Grid x:Name="StandardContainer">

src/App/Controls/Player/Related/LiveMessageView.xaml.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Richasy. All rights reserved.
 
 using System;
+using System.Threading.Tasks;
 
 namespace Richasy.Bili.App.Controls.Player.Related
 {
@@ -15,12 +16,23 @@ public sealed partial class LiveMessageView : PlayerComponent
         public LiveMessageView()
         {
             this.InitializeComponent();
-            ViewModel.RequestLiveMessageScrollToBottom += OnRequestLiveMessageScrollToBottom;
+            ViewModel.RequestLiveMessageScrollToBottom += OnRequestLiveMessageScrollToBottomAsync;
         }
 
-        private void OnRequestLiveMessageScrollToBottom(object sender, EventArgs e)
+        private async void OnRequestLiveMessageScrollToBottomAsync(object sender, EventArgs e)
         {
-            ScrollViewer.ChangeView(0, (ScrollViewer.ExtentHeight + ScrollViewer.ScrollableHeight) * 2, 1);
+            await Task.Delay(50);
+            ScrollViewer.ChangeView(0, double.MaxValue, 1);
+        }
+
+        private void OnViewChanged(object sender, Windows.UI.Xaml.Controls.ScrollViewerViewChangedEventArgs e)
+        {
+            if (!e.IsIntermediate)
+            {
+                // 这里的逻辑是，如果滚动到了底部，则表示允许视图自动滚动，
+                // 如果不在底部，表示用户自己滚动了视图，此时则不再自动滚动.
+                ViewModel.IsLiveMessageAutoScroll = ScrollViewer.VerticalOffset + ScrollViewer.ViewportHeight >= ScrollViewer.ExtentHeight - 50;
+            }
         }
     }
 }

src/ViewModels/ViewModels.Uwp/Common/PlayerViewModel/PlayerViewModel.Live.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Richasy. All rights reserved.
 
 using System;
+using System.Collections.ObjectModel;
+using System.Linq;
 using Richasy.Bili.Models.App.Args;
 using Richasy.Bili.Models.BiliBili;
 using Richasy.Bili.Models.Enums;
@@ -25,6 +27,11 @@ await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
                     var data = e.Data as LiveDanmakuMessage;
                     LiveDanmakuCollection.Add(data);
                     NewLiveDanmakuAdded?.Invoke(this, data);
+                    if (LiveDanmakuCollection.Count > 1000)
+                    {
+                        var saveMessages = LiveDanmakuCollection.ToList().Skip(600);
+                        LiveDanmakuCollection = new ObservableCollection<LiveDanmakuMessage>(saveMessages);
+                    }
                 }
             });
         }

src/ViewModels/ViewModels.Uwp/Common/PlayerViewModel/PlayerViewModel.Methods.cs

@@ -42,6 +42,7 @@ private void Reset()
             IsPlayInformationError = false;
             IsCurrentEpisodeInPgcSection = false;
             IsShowEmptyLiveMessage = true;
+            IsLiveMessageAutoScroll = true;
             CurrentPlayLine = null;
             CurrentLiveQuality = null;
             _audioList.Clear();

src/ViewModels/ViewModels.Uwp/Common/PlayerViewModel/PlayerViewModel.Properties.cs

@@ -609,6 +609,12 @@ public partial class PlayerViewModel
         [Reactive]
         public string LivePartition { get; set; }
 
+        /// <summary>
+        /// 直播消息是否自动滚动.
+        /// </summary>
+        [Reactive]
+        public bool IsLiveMessageAutoScroll { get; set; }
+
         private BiliController Controller { get; } = BiliController.Instance;
     }
 }

src/ViewModels/ViewModels.Uwp/Common/PlayerViewModel/PlayerViewModel.cs

@@ -511,7 +511,7 @@ private void OnLiveDanmakuCollectionChanged(object sender, NotifyCollectionChang
             var count = LiveDanmakuCollection.Count;
             IsShowEmptyLiveMessage = count == 0;
 
-            if (count > 0)
+            if (count > 0 && IsLiveMessageAutoScroll)
             {
                 RequestLiveMessageScrollToBottom?.Invoke(this, EventArgs.Empty);
             }