Aggressive GC after window closed

QuickLook/Helpers/ProcessHelper.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Threading.Tasks;
+
+namespace QuickLook.Helpers
+{
+    internal class ProcessHelper
+    {
+        // ReSharper disable once InconsistentNaming
+        public static void PerformAggressiveGC()
+        {
+            // delay some time to make sure that all windows are closed
+            Task.Delay(1000).ContinueWith(t => GC.Collect(GC.MaxGeneration));
+        }
+    }
+}

QuickLook/MainWindowTransparent.xaml.cs

@@ -4,10 +4,12 @@ using System.IO;
 using System.Runtime.ExceptionServices;
 using System.Windows;
 using System.Windows.Forms;
+using System.Windows.Input;
 using System.Windows.Threading;
 using QuickLook.Helpers;
 using QuickLook.Helpers.BlurLibrary;
 using QuickLook.Plugin;
+using KeyEventArgs = System.Windows.Forms.KeyEventArgs;
 
 namespace QuickLook
 {
@@ -81,15 +83,12 @@ namespace QuickLook
 
         internal void UnloadPlugin()
         {
-            // clear ref to control
-            //container.Content = null;
-
             ContextObject.Reset();
 
             _plugin?.Cleanup();
             _plugin = null;
 
-            GC.Collect();
+            ProcessHelper.PerformAggressiveGC();
         }
 
         internal void BeginShow(IViewer matchedPlugin, string path)
@@ -97,6 +96,8 @@ namespace QuickLook
             _path = path;
             _plugin = matchedPlugin;
 
+            ContextObject.ViewerWindow = this;
+
             // get window size before showing it
             _plugin.Prepare(path, ContextObject);
 
@@ -150,8 +151,14 @@ namespace QuickLook
 
         internal void BeginHide()
         {
+            // the focused element will not processed by GC: https://stackoverflow.com/questions/30848939/memory-leak-due-to-window-efectivevalues-retention
+            FocusManager.SetFocusedElement(this, null);
+            Keyboard.ClearFocus();
+
             UnloadPlugin();
             Hide();
+
+            ProcessHelper.PerformAggressiveGC();
         }
     }
 }

QuickLook/Properties/Settings.Designer.cs

@@ -8,21 +8,17 @@
 // </auto-generated>
 //------------------------------------------------------------------------------
 
-namespace QuickLook.Properties
-{
+namespace QuickLook.Properties {
     
     
     [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
-    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "11.0.0.0")]
-    internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase
-    {
+    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "15.1.0.0")]
+    internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase {
         
         private static Settings defaultInstance = ((Settings)(global::System.Configuration.ApplicationSettingsBase.Synchronized(new Settings())));
         
-        public static Settings Default
-        {
-            get
-            {
+        public static Settings Default {
+            get {
                 return defaultInstance;
             }
         }

QuickLook/QuickLook.csproj

@@ -8,7 +8,7 @@
     <OutputType>WinExe</OutputType>
     <RootNamespace>QuickLook</RootNamespace>
     <AssemblyName>QuickLook</AssemblyName>
-    <TargetFrameworkVersion>v4.5.2</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <ProjectTypeGuids>{60dc8134-eba5-43b8-bcc9-bb4bc16c2548};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <WarningLevel>4</WarningLevel>
@@ -28,6 +28,7 @@
     <ApplicationVersion>1.0.0.%2a</ApplicationVersion>
     <UseApplicationTrust>false</UseApplicationTrust>
     <BootstrapperEnabled>true</BootstrapperEnabled>
+    <TargetFrameworkProfile />
   </PropertyGroup>
   <PropertyGroup>
     <ApplicationIcon>Resources\app.ico</ApplicationIcon>
@@ -108,6 +109,7 @@
     <Compile Include="Helpers\BlurLibrary\PlatformsImpl\Windows8WindowBlurController.cs" />
     <Compile Include="Helpers\BlurLibrary\PlatformsImpl\WindowsVistaWindowBlurController.cs" />
     <Compile Include="Helpers\FileHelper.cs" />
+    <Compile Include="Helpers\ProcessHelper.cs" />
     <Compile Include="MainWindowNoTransparent.cs" />
     <Compile Include="NativeMethods\Shell32\IShellLink.cs" />
     <Compile Include="NativeMethods\Shell32\IWshShell.cs" />