diff --git a/installer/Installer/Model.cs b/installer/Installer/Model.cs
index 18128c4..9ffd19f 100644
--- a/installer/Installer/Model.cs
+++ b/installer/Installer/Model.cs
@@ -835,7 +835,7 @@ namespace Downloader
             private static void Download()
             {
                 Tencent_cos_download Downloader = new Tencent_cos_download();
-                int newFile = 0, updateFile = 0;
+                int newFile = 0;
                 int totalnew = newFileName.Count, totalupdate = updateFileName.Count;
                 filenum = totalnew + totalupdate;
                 updateFailed.Clear();
@@ -1573,24 +1573,25 @@ namespace Downloader
                 ServerDebugAndPythonVisit,
             }
 
+            // !!! 目前此类的各个静态成员从未被赋值过
             public class RunInfo                //UI需要在调用Launch函数前保证其中数据已经更新并有效
             {
-                static public RunMode mode;
-                static public string? IP;
-                static public int port;
-                static public int studentCount;
-                static public int trickerCount;
-                static public int gameTimeSec;
-                static public string? playbackFileName;
-                static public int characterID;
-                static public int type;
-                static public bool saveDebugLog;
-                static public bool showDebugLog;
-                static public bool warningOnly;
-                static public bool visiting;
-                static public int occupation;
-                static public List<int>? playerId = new List<int>();           //两者长度必须与studentCount + trickerCount一致
-                static public List<string>? filePath = new List<string>();
+                public static RunMode mode = default;
+                public static string? IP = null;
+                public static int port = 0;
+                public static int studentCount = 0;
+                public static int trickerCount = 0;
+                public static int gameTimeSec = 0;
+                public static string? playbackFileName = null;
+                public static int characterID = 0;
+                public static int type = 0;
+                public static bool saveDebugLog = false;
+                public static bool showDebugLog = false;
+                public static bool warningOnly = false;
+                public static bool visiting = false;
+                public static int occupation = 0;
+                public static List<int>? playerId = new List<int>();           //两者长度必须与studentCount + trickerCount一致
+                public static List<string>? filePath = new List<string>();
             }
 
             /// <summary>
diff --git a/installer/Installer/ViewModel.cs b/installer/Installer/ViewModel.cs
index 0baa631..4cb2ac1 100644
--- a/installer/Installer/ViewModel.cs
+++ b/installer/Installer/ViewModel.cs
@@ -20,8 +20,8 @@ namespace starter.viewmodel.settings
     public class SettingsViewModel : NotificationObject
     {
         //定义BackgroundWorker
-        BackgroundWorker asyncDownloader;
-        BackgroundWorker asyncUpdater;
+        BackgroundWorker? asyncDownloader;
+        BackgroundWorker? asyncUpdater;
         BackgroundWorker asyncInitializer;
         /// <summary>
         /// Model object
@@ -202,6 +202,11 @@ namespace starter.viewmodel.settings
 
         private void AsyncUpdater_DoWork(object? sender, DoWorkEventArgs e)
         {
+            if (asyncUpdater is null)
+            {
+                throw new InvalidOperationException("asyncUpdater is null");
+            }
+
             if (asyncUpdater.CancellationPending)
             {
                 e.Cancel = true;
@@ -230,6 +235,11 @@ namespace starter.viewmodel.settings
 
         private void AsyncDownloader_DoWork(object? sender, DoWorkEventArgs e)
         {
+            if (asyncDownloader is null)
+            {
+                throw new InvalidOperationException("asyncDownloader is null");
+            }
+
             if (asyncDownloader.CancellationPending)
             {
                 e.Cancel = true;
@@ -710,7 +720,7 @@ namespace starter.viewmodel.settings
                                 {
                                     Status = SettingsModel.Status.successful;
                                 }*/
-                                if (asyncDownloader.IsBusy)
+                                if (asyncDownloader?.IsBusy ?? true)
                                     return;
                                 else
                                 {
@@ -776,7 +786,7 @@ namespace starter.viewmodel.settings
                             }
                             else
                                 Status = SettingsModel.Status.error;*/
-                            if (asyncUpdater.IsBusy)
+                            if (asyncUpdater?.IsBusy ?? true)
                                 return;
                             else
                                 asyncUpdater.RunWorkerAsync("Manual");
@@ -905,7 +915,7 @@ namespace starter.viewmodel.settings
                         {
                             Status = SettingsModel.Status.working;
                             this.RaisePropertyChanged("ProgressVis");
-                            if (asyncUpdater.IsBusy)
+                            if (asyncUpdater?.IsBusy ?? true)
                                 return;
                             else
                                 asyncUpdater.RunWorkerAsync("Auto");