PowerToys/src/modules/previewpane

PowerPreview

Adding Custom Preview Handlers to Windows File Explorer Preview Pane.

Overview · Developing · MSIX Integration · Contributing »

Overview

Preview handlers are called when an item is selected to show a lightweight, rich, read-only preview of the file's contents in the view's reading pane. This is done without launching the file's associated application. Figure 1 shows an example of a preview handler that preview a .md file type. Please follow this documentation to start developing a preview handler, when done, continue with this documentation to learn how to integrate a preview handler into PowerToys.

Figure 1 : Mark Down Preview Handler Demo

Developing

We have already done most of the development work in the PreviewHandlerCommon common project. To add a preview for the file type of .xyz:

• Add a new .NET project in the preview pane folder.
• Add a reference to the PreviewHandlerCommon common project.
• Create your preview handler class and extend the FileBasedPreviewHandler class. See an example below:

using System;
using System.Runtime.InteropServices;
using Common;

namespace XYZPreviewHandler
{
    /// <summary>
    /// Implementation of preview handler for .xyz files.
    /// GUID = CLSID / CLASS ID.
    /// </summary>
    [Guid("xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx")]
    [ClassInterface(ClassInterfaceType.None)]
    [ComVisible(true)]
    public class XYZPreviewHandler : FileBasedPreviewHandler
    {
        private XYZPreviewHandlerControl xyzPreviewHandlerControl;

        /// Call your rendering method here.
        public override void DoPreview()
        {
            this.xyzPreviewHandlerControl.DoPreview(this.FilePath);
        }

        protected override IPreviewHandlerControl CreatePreviewHandlerControl()
        {
            this.xyzPreviewHandlerControl = new xyzPreviewHandlerControl();
            return this.xyzPreviewHandlerControl;
        }
    }
}

Create a separate Preview Handler Control class and extend the FormHandlerControl Class.

using Common;

namespace XYZPreviewHandler
{
    public class XYZPreviewHandlerControl : FormHandlerControl
    {
        public XYZPreviewHandlerControl()
        {
            // ... do your initializations here.
        }

        public override void DoPreview<T>(T dataSource)
        {
            // ... add your preview rendering code here.
        }
    }
}

Integrate the Preview Handler into PowerToys Settings:

Navigate to the powerpreview project and edit the powerpreview.h file. Add the following Settings Object instance to m_previewHandlers settings objects array in the constructor initialization:

// XYZ Preview Handler Settings Object.
FileExplorerPreviewSettings(
    false,
    L"<--YOUR_TOGGLE_CONTROL_ID-->",
    L"<--A description of your preview handler-->",
    L"xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx", // your preview handler CLSID.
    L"<--A display name for your preview handler-->") 

Installation

MSI

To add a new Previewer update the Product.wxs file in PowerToysSetup similar to existing Previewer to register the Preview Handler. More details about registration of Preview Handlers can be found here.

<Component Id="Module_PowerPreview" Guid="FF1700D5-1B07-4E07-9A62-4D206645EEA9" Win64="yes">
        <!-- Files to include dll's for new Previewer and it's dependencies -->
        <File Source="$(var.BinX64Dir)\modules\XYZPreviewer.dll" />
        <File Source="$(var.BinX64Dir)\modules\Dependency.dll" />
      </Component>
      <Component Id="Module_PowerPreview_PerUserRegistry" Guid="CD90ADC0-7CD5-4A62-B0AF-23545C1E6DD3" Win64="yes">
        <!-- Added a separate component for Per-User registry changes -->
        <!-- Registry Key for Class Registration of new Preview Handler -->
        <RegistryKey Root="HKCU" Key="Software\Classes\CLSID\{ddee2b8a-6807-48a6-bb20-2338174ff779}">
          <RegistryValue Type="string" Value="XYZPreviewHandler.XYZPreviewHandler" />
          <RegistryValue Type="string" Name="DisplayName" Value="XYZ Preview Handler" />
          <RegistryValue Type="string" Name="AppID" Value="{CF142243-F059-45AF-8842-DBBE9783DB14}" />
          <RegistryValue Type="string" Key="Implemented Categories\{62C8FE65-4EBB-45e7-B440-6E39B2CDBF29}" Value=""/>
          <RegistryValue Type="string" Key="InprocServer32" Value="mscoree.dll" />
          <RegistryValue Type="string" Key="InprocServer32" Name="Assembly" Value="SvgPreviewHandler, Version=$(var.Version).0, Culture=neutral" />
          <RegistryValue Type="string" Key="InprocServer32" Name="Class" Value="XYZPreviewHandler.XYZPreviewHandler" />
          <RegistryValue Type="string" Key="InprocServer32" Name="RuntimeVersion" Value="v4.0.30319" />
          <RegistryValue Type="string" Key="InprocServer32" Name="ThreadingModel" Value="Both" />
          <RegistryValue Type="string" Key="InprocServer32" Name="CodeBase" Value="file:///[ModulesInstallFolder]XYZPreviewHandler.dll" />
          <RegistryValue Type="string" Key="InprocServer32\$(var.Version).0" Name="Assembly" Value="XYZPreviewHandler, Version=$(var.Version).0, Culture=neutral" />
          <RegistryValue Type="string" Key="InprocServer32\$(var.Version).0" Name="Class" Value="XYZPreviewHandler.XYZPreviewHandler" />
          <RegistryValue Type="string" Key="InprocServer32\$(var.Version).0" Name="RuntimeVersion" Value="v4.0.30319" />
          <RegistryValue Type="string" Key="InprocServer32\$(var.Version).0" Name="CodeBase" Value="file:///[ModulesInstallFolder]XYZPreviewer.dll" />
        </RegistryKey>
        <!-- Add new previewer to preview handlers list -->
        <RegistryKey Root="HKCU" Key="Software\Microsoft\Windows\CurrentVersion\PreviewHandlers">
          <RegistryValue Type="string" Name="{Clsid-Guid}" Value="Name of the Previewer" />
        </RegistryKey>
        <!-- Add file type association for the new Previewer -->
        <RegistryKey Root="HKCU" Key="Software\Classes\.xyz\shellex">
          <RegistryValue Type="string" Key="{8895b1c6-b41f-4c1c-a562-0d564250836f}" Value="{Clsid-Guid}" />
        </RegistryKey>
      </Component>

MSIX

Warning: There are known issues(Issue - 1446, Issue - 1545) with MSIX Installation of Preview Handlers and it's not fully supported.

To add a new Previewer with MSIX update the appxmanifest.xml file to add file type association for preview handler and add SurrogateServer element with class registration. MSIX currently doesn't support .Net Assembly activation with SurrogateServer the logic used is shim the activation by using native dll. dllmain.cpp in powerpreview project expose the DLLGetClassObject method which is used to activate .net Assembly by using CoGetClassObject.

Changes required in appxmanifest.xml:

        <!-- File Type Association for new Preview Handler -->
        <!-- More details: https://docs.microsoft.com/en-us/uwp/schemas/appxpackage/uapmanifestschema/element-desktop2-desktoppreviewhandler -->
        <uap:Extension Category="windows.fileTypeAssociation">
          <uap3:FileTypeAssociation Name="xyzpreviewhandler" desktop2:AllowSilentDefaultTakeOver="true">
            <uap:SupportedFileTypes>
              <uap:FileType>.xyz</uap:FileType>
            </uap:SupportedFileTypes>
            <desktop2:DesktopPreviewHandler Clsid="74619BDA-A66B-451D-864C-A7726F5FE650"/>
          </uap3:FileTypeAssociation>
        </uap:Extension>
        <com:Extension Category="windows.comServer">
          <com:ComServer>
            <com:SurrogateServer DisplayName="Preview Handler" AppId="E39A92FE-D89A-417B-9B9D-F0B6BD564B36" SystemSurrogate="PreviewHost">
              <com:Class Id="Shim-Activator-Clsid-Guid" Path="modules\powerpreview.dll" ThreadingModel="Both"/>
            </com:SurrogateServer>
          </com:ComServer>
        </com:Extension>

Update the PackagingLayout.xml to include dll's required by the new Preview Handler.

        <File DestinationPath="modules\XYZPreviewHandler.dll" SourcePath="..\..\x64\Release\modules\XYZPreviewHandler.dll"/>
        <File DestinationPath="modules\XYZDependency.dll" SourcePath="..\..\x64\Release\modules\XYZDependency.dll"/>

Add the actual Clsid of the new preview handler in CLSID.h in powerpreview project and class registration registry changes in registry.dat similar to existing preview handler. To update the registry.dat mount the registry hive on a empty key in registry by using reggedit.exe and add registry key for class registartion for the new preview handler similar to MSI class registration and existing preview handlers. And export the updated registry.dat hive also export the registry.reg file for making the contents in registy.dat visible in source code.

// CLSID used in manifest file for Preview Handler.
const CLSID CLSID_SHIMActivateXYZPreviewHandler = { valid - guid };

// Actual Clsid Guid.
const CLSID CLSID_XYZPreviewHandler = { valid - guid };

// Pairs of NativeClsid vs ManagedClsid used for preview handlers.
const std::vector<std::pair<CLSID, CLSID>> NativeToManagedClsid({
    { CLSID_SHIMActivateXYZPreviewHandler, CLSID_XYZPreviewHandler }
});

Managing Preview Handlers

After successful integration, your preview handler should appear in the PowerToys settings UI under the File Explorer Preview Tab as shown in Figure 2 below. In here you should be able to enable and disable your preview handler.

Figure 2 : Settings UI - File Explorer Preview Tab

In the general settings of the Settings UI, you should be able to disable and enable all the preview handlers all at once. See Figure 3.

Figure 3 : Settings UI - General Settings Tab

Contributing

Coding Guidance

Working With Strings

YOU SHOULD NOT have hardcoded strings in your C++ code. Instead, use the following guidelines to add strings to your code. Add the ID of your string to the resource file. XXX must be a unique int in the list (mostly the int ID of the last string id plus one):

• resource.h:

#define IDS_PREVPANE_XYZ_SETTINGS_DISPLAYNAME                    XXX

• powerpreview.rc under strings table:

IDS_PREVPANE_XYZ_SETTINGS_DISPLAYNAME               L"XYZ Preview Handler"

• Use the GET_RESOURCE_STRING(UINT resource_id) method to consume strings in your code.

#include <common.h>

extern "C" IMAGE_DOS_HEADER __ImageBase;

std::wstring GET_RESOURCE_STRING(IDS_PREVPANE_XYZ_SETTINGS_DISPLAYNAME)

More On Coding Guidance

Please review these brief docs below relating to our coding standards etc.

👉 If you find something missing from these docs, feel free to contribute to any of our documentation files anywhere in the repository (or make some new ones!)

• Coding Style
• Code Organization