Move show msgbox to view

Author: VictoriousRaptor

Plugins/Flow.Launcher.Plugin.Program/AddProgramSource.xaml.cs

@@ -30,15 +30,15 @@ private void BtnCancel_OnClick(object sender, RoutedEventArgs e)
         private void BtnAdd_OnClick(object sender, RoutedEventArgs e)
         {
             var status = ViewModel.AddOrUpdate();
-            if (status == null)
+            bool modified = status.Item1;
+            string msg = status.Item2;
+            if (modified == false && msg != null)
             {
-                return; // Invalid
-            }
-            else
-            {
-                DialogResult = status ?? false;
-                Close();
+                MessageBox.Show(msg);  // Invalid
+                return;
             }
+            DialogResult = modified;
+            Close();
         }
     }
 }

Plugins/Flow.Launcher.Plugin.Program/ViewModels/AddProgramSourceViewModel.cs

@@ -80,42 +80,37 @@ public void Browse()
             }
         }
 
-        public bool? AddProgramSource()
+        public (bool, string) AddProgramSource()
         {
             if (!Directory.Exists(Location))
             {
-                System.Windows.MessageBox.Show(API.GetTranslation("flowlauncher_plugin_program_invalid_path"));
-                return null;
+                return (false, API.GetTranslation("flowlauncher_plugin_program_invalid_path"));
             }
             else if (DuplicateSource(Location))
             {
-                System.Windows.MessageBox.Show(API.GetTranslation("flowlauncher_plugin_program_duplicate_program_source"));
-                return null;
+                return (false, API.GetTranslation("flowlauncher_plugin_program_duplicate_program_source"));
             }
             else
             {
                 var source = new ProgramSource(Location, Enabled);
                 Settings.ProgramSources.Insert(0, source);
                 ProgramSetting.ProgramSettingDisplayList.Add(source);
-                return true;
+                return (true, null);
             }
         }
 
-        public bool? UpdateProgramSource()
+        public (bool, string) UpdateProgramSource()
         {
             // Separate checks to avoid changing UniqueIdentifier of UWP when changing Enabled
             if (LocationModified)
             {
                 if (!Directory.Exists(Location))
                 {
-                    System.Windows.MessageBox.Show(API.GetTranslation("flowlauncher_plugin_program_invalid_path"));
-                    return null;
+                    return (false, API.GetTranslation("flowlauncher_plugin_program_invalid_path"));
                 }
                 else if (DuplicateSource(Location))
                 {
-                    // No need to check win32 or uwp, just override them
-                    System.Windows.MessageBox.Show(API.GetTranslation("flowlauncher_plugin_program_duplicate_program_source"));
-                    return null;
+                    return (false, API.GetTranslation("flowlauncher_plugin_program_duplicate_program_source"));
                 }
                 else
                 {
@@ -126,10 +121,10 @@ public void Browse()
             {
                 Source.Enabled = Enabled;
             }
-            return StatusModified || LocationModified;
+            return (StatusModified || LocationModified, null);
         }
 
-        public bool? AddOrUpdate()
+        public (bool, string) AddOrUpdate()
         {
             if (Source == null)
             {