[PreviewPane] Fix form positioning issues (#34035)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

This PR aims to fix some positioning issues of the form used as preview
handler.
It fixes the following issues:
1. The floating window, detached from Explorer that sometimes appears:
#33491 #27475 #24985
2. The **CoreWebView2 members cannot be accessed after the WebView2
control is disposed** crash: #27276
3. `PowerToys.*.PreviewHandler.exe` process leak

### Repro steps for issue 1
- Navigate through files in a folder invoking their preview handler
- Minimize/Restore Explorer quickly (spam WIN+D usually works)
- 2 weird issues happen:
  - Some `PowerToys.*.PreviewHandler.exe` processes are leaked
- Some `PowerToys.*.PreviewHandler.exe` are started with a `NULL` `HWND`

![Screenshot 2024-07-27
**200207](https://github.com/user-attachments/assets/5cb6c857-ad93-422a-8c5b-47bd1c492dce)

This happens because
[IPreviewHandler::DoPreview](https://learn.microsoft.com/windows/win32/api/shobjidl_core/nf-shobjidl_core-ipreviewhandler-dopreview)
is called multiple times and sometimes before calling
[IPreviewHandler::SetWindow](https://learn.microsoft.com/windows/win32/api/shobjidl_core/nf-shobjidl_core-ipreviewhandler-setwindow).

When the managed previewer try to set the parent of the form to the
`NULL` `HWND`, the desktop window is used instead, resulting in the
floating preview window being displayed.
Reference:
https://learn.microsoft.com/windows/win32/api/winuser/nf-winuser-setparent#parameters


5d77874382/src/modules/previewpane/common/controls/FormHandlerControl.cs (L136)

### Repro steps for issue 2
- Preview a file
- Restart `explorer.exe` process
- Make sure `PowerToys.*.PreviewHandler.exe` is leaked and still running
- Preview the same file again
- Preview is displayed (another process is launched)
- Minimize Explorer

What happens here is that the form of the old process have an invalid
`HWND` as parent but receive the `SetRect` for some reason.

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] **Closes:** #33491 #27475 #24985 #27276
- [ ] **Communication:** I've discussed this with core contributors
already. If work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end user facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

- Don't start preview pane process when `HWND` is `NULL`
- Terminate the preview pane process when setting parent fails
- Prevent leaking processes closing them when a new preview is requested
- Fixed an issue where PDF and SVG previews weren't updated after
restoring Explorer
- Added some error handling in the `UpdateWindowBounds` method of the
managed preview
- Terminate the preview pane when the `SetRect` event is received but
the parent `HWND` has become invalid

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

- Manually tested all preview panes also using multiple Explorer windows
- Validated that when Explorer is minimized/restored the preview is
updated
- Tested the preview pane resize
- Validated that no window, no taskbar icon and no errors appear on both
repro steps

src/modules/previewpane/GcodePreviewHandler/Program.cs

@@ -36,15 +36,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Gcode
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new GcodePreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.GcodePreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/GcodePreviewHandlerCpp/GcodePreviewHandler.cpp

@@ -159,9 +159,9 @@ IFACEMETHODIMP GcodePreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start GcodePreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start GcodePreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
         Logger::info(L"Starting GcodePreviewHandler.exe");
@@ -189,6 +189,13 @@ IFACEMETHODIMP GcodePreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/MarkdownPreviewHandler/Program.cs

@@ -36,15 +36,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Markdown
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new MarkdownPreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.MarkdownPreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/MarkdownPreviewHandlerCpp/MarkdownPreviewHandler.cpp

@@ -160,9 +160,9 @@ IFACEMETHODIMP MarkdownPreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start MarkdownPreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start MarkdownPreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
         Logger::info(L"Starting MarkdownPreviewHandler.exe");
@@ -190,6 +190,13 @@ IFACEMETHODIMP MarkdownPreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/MonacoPreviewHandler/Program.cs

@@ -39,15 +39,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Monaco
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new MonacoPreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.DevFilesPreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/MonacoPreviewHandlerCpp/MonacoPreviewHandler.cpp

@@ -159,9 +159,9 @@ IFACEMETHODIMP MonacoPreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start MonacoPreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start MonacoPreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
 
@@ -189,6 +189,13 @@ IFACEMETHODIMP MonacoPreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/PdfPreviewHandler/Program.cs

@@ -35,15 +35,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Pdf
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new PdfPreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.PdfPreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/PdfPreviewHandlerCpp/PdfPreviewHandler.cpp

@@ -147,6 +147,7 @@ IFACEMETHODIMP PdfPreviewHandler::SetRect(const RECT* prc)
                 }
             }
         }
+        m_rcParent = *prc;
         hr = S_OK;
     }
     return hr;
@@ -156,9 +157,9 @@ IFACEMETHODIMP PdfPreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start PdfPreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start PdfPreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
         Logger::info(L"Starting PdfPreviewHandler.exe");
@@ -186,6 +187,13 @@ IFACEMETHODIMP PdfPreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/QoiPreviewHandler/Program.cs

@@ -36,15 +36,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Qoi
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new QoiPreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.QoiPreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/QoiPreviewHandlerCpp/QoiPreviewHandler.cpp

@@ -159,9 +159,9 @@ IFACEMETHODIMP QoiPreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start QoiPreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start QoiPreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
         Logger::info(L"Starting QoiPreviewHandler.exe");
@@ -189,6 +189,13 @@ IFACEMETHODIMP QoiPreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/SvgPreviewHandler/Program.cs

@@ -36,15 +36,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Svg
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new SvgPreviewControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.SvgPreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
+                            Rectangle s = default;
-                            _previewHandlerControl.SetRect(s);
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);

src/modules/previewpane/SvgPreviewHandlerCpp/SvgPreviewHandler.cpp

@@ -149,6 +149,7 @@ IFACEMETHODIMP SvgPreviewHandler::SetRect(const RECT* prc)
                 }
             }
         }
+        m_rcParent = *prc;
         hr = S_OK;
     }
     return hr;
@@ -158,9 +159,9 @@ IFACEMETHODIMP SvgPreviewHandler::DoPreview()
 {
     try
     {
-        if (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0)
+        if (m_hwndParent == NULL || (m_rcParent.left == 0 && m_rcParent.top == 0 && m_rcParent.right == 0 && m_rcParent.bottom == 0))
         {
-            // Postponing Start SvgPreviewHandler.exe, position not yet initialized. preview will be done after initialisation
+            // Postponing Start SvgPreviewHandler.exe, parent and position not yet initialized. Preview will be done after initialisation.
             return S_OK;
         }
         Logger::info(L"Starting SvgPreviewHandler.exe");
@@ -188,6 +189,13 @@ IFACEMETHODIMP SvgPreviewHandler::DoPreview()
         sei.lpParameters = cmdLine.c_str();
         sei.nShow = SW_SHOWDEFAULT;
         ShellExecuteEx(&sei);
+
+        // Prevent to leak processes: preview is called multiple times when minimizing and restoring Explorer window
+        if (m_process)
+        {
+            TerminateProcess(m_process, 0);
+        }
+
         m_process = sei.hProcess;
     }
     catch (std::exception& e)

src/modules/previewpane/common/cominterop/NativeMethods.cs

@@ -37,5 +37,8 @@ namespace PreviewHandlerCommon.ComInterop
         [DllImport("user32.dll", SetLastError = true)]
         [return: MarshalAs(UnmanagedType.Bool)]
         public static extern bool GetClientRect(IntPtr hWnd, ref Common.ComInterlop.RECT rect);
+
+        [DllImport("user32.dll")]
+        public static extern bool IsWindow(IntPtr hWnd);
     }
 }

src/modules/previewpane/common/controls/FormHandlerControl.cs

@@ -73,9 +73,9 @@ namespace Common
         }
 
         /// <inheritdoc />
-        public void SetRect(Rectangle windowBounds)
+        public bool SetRect(Rectangle windowBounds)
         {
-            this.UpdateWindowBounds(parentHwnd, windowBounds);
+            return this.UpdateWindowBounds(parentHwnd, windowBounds);
         }
 
         /// <inheritdoc />
@@ -85,10 +85,10 @@ namespace Common
         }
 
         /// <inheritdoc />
-        public void SetWindow(IntPtr hwnd, Rectangle rect)
+        public bool SetWindow(IntPtr hwnd, Rectangle rect)
         {
             this.parentHwnd = hwnd;
-            this.UpdateWindowBounds(hwnd, rect);
+            return this.UpdateWindowBounds(hwnd, rect);
         }
 
         /// <inheritdoc />
@@ -118,12 +118,18 @@ namespace Common
         /// <summary>
         /// Update the Form Control window with the passed rectangle.
         /// </summary>
-        public void UpdateWindowBounds(IntPtr hwnd, Rectangle newBounds)
+        public bool UpdateWindowBounds(IntPtr hwnd, Rectangle newBounds)
         {
+            if (hwnd == IntPtr.Zero || !NativeMethods.IsWindow(hwnd))
+            {
+                // If the HWND is IntPtr.Zero the desktop window will be used as parent.
+                return false;
+            }
+
             if (this.Disposing || this.IsDisposed)
             {
                 // For unclear reasons, this can be called when handling an error and the form has already been disposed.
-                return;
+                return false;
             }
 
             // We must set the WS_CHILD style to change the form to a control within the Explorer preview pane
@@ -133,7 +139,10 @@ namespace Common
                 _ = NativeMethods.SetWindowLong(Handle, gwlStyle, windowStyle | wsChild);
             }
 
-            NativeMethods.SetParent(Handle, hwnd);
+            if (NativeMethods.SetParent(Handle, hwnd) == IntPtr.Zero)
+            {
+                return false;
+            }
 
             if (newBounds.IsEmpty)
             {
@@ -146,6 +155,8 @@ namespace Common
             {
                 Bounds = newBounds;
             }
+
+            return true;
         }
     }
 }

src/modules/previewpane/common/controls/IPreviewHandlerControl.cs

@@ -58,14 +58,16 @@ namespace Common
         /// Directs the control to change the area within the parent hwnd that it draws into.
         /// </summary>
         /// <param name="windowBounds">Instance of Rectangle defining the area.</param>
-        void SetRect(Rectangle windowBounds);
+        /// <returns><see langword="true"/> if the operation was successful; otherwise, <see langword="false"/>.</returns>
+        bool SetRect(Rectangle windowBounds);
 
         /// <summary>
-        /// Sets the parent window of the previewer window, as well as the area within the parent to be used for the previewer window..
+        /// Sets the parent window of the previewer window, as well as the area within the parent to be used for the previewer window.
         /// </summary>
         /// <param name="hwnd">Pointer to the parent window handle.</param>
         /// <param name="rect">Instance of Rectangle defining the area.</param>
-        void SetWindow(IntPtr hwnd, Rectangle rect);
+        /// <returns><see langword="true"/> if the operation was successful; otherwise, <see langword="false"/>.</returns>
+        bool SetWindow(IntPtr hwnd, Rectangle rect);
 
         /// <summary>
         /// Called by Preview Handler to start the preview.