# File Explorer
## End user facing:
[Please visit our overview](https://aka.ms/PowerToysOverview_FileExplorerAddOns)
## Developing
We have already done most of the development work in the [PreviewHandlerCommon](./common/cominterop/IPreviewHandler.cs) 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:
```csharp
using System;
using System.Runtime.InteropServices;
using Common;
namespace XYZPreviewHandler
{
///
/// Implementation of preview handler for .xyz files.
/// GUID = CLSID / CLASS ID.
///
[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.
```csharp
using Common;
namespace XYZPreviewHandler
{
public class XYZPreviewHandlerControl : FormHandlerControl
{
public XYZPreviewHandlerControl()
{
// ... do your initializations here.
}
public override void DoPreview(T dataSource)
{
// ... add your preview rendering code here.
}
}
}
```
#### Integrate the Preview Handler into PowerToys Settings:
Navigate to the [powerpreview](../previewpane/powerpreview/powerpreview.h) project and edit the `powerpreview.h` file. Add the following Settings Object instance to `m_previewHandlers` settings objects array in the constructor initialization:
```cpp
// 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 (Recommended)
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.](https://docs.microsoft.com/en-us/windows/win32/shell/how-to-register-a-preview-handler)
```xml
```
### Directly registering/unregistering DLL's
**[Important] This method of registering Preview Handler DLL's is not recommended. It could lead to registry corruption.**
#### Registering Preview Handler
1. Restart Visual studio as administrator.
2. Sign `XYZPreviewHandler` and it's dependencies. To sign an assembly in VS, follow steps given [here](https://docs.microsoft.com/en-us/dotnet/standard/assembly/sign-strong-name#create-and-sign-an-assembly-with-a-strong-name-by-using-visual-studio).
3. Build `XYZPreviewHandler` project.
4. Open developer command prompt from `Tools > Command Line > Developer Command Prompt`.
5. Run following command for each nuget and project dependency to add them to Global Assembly Cache(GAC).
```
gacutil -i
```
6. Run following commands to register preview handler.
```
cd C:\Windows\Microsoft.NET\Framework64\4.0.x.x
gacutil -i
RegAsm.exe /codebase
```
7. Restart Windows Explorer process.
#### Unregistering Preview Handler
1. Run following commands in elevated developer command prompt to unregister preview handler.
```
cd C:\Windows\Microsoft.NET\Framework64\4.0.x.x
RegAsm.exe /unregister
gacutil -u XYZPreviewHandler
```
## Debugging
Since in-process preview handlers run under a surrogate hosting process (prevhost.exe by default), to debug a preview handler, you need to attach the debugger to the host process.
1. Click on a file with registered extension to start host process.
2. Attach debugger in Visual studio from `Debug->Attach to Process` and select `prevhost.exe` with type `Managed(version), x64`.
## Managing Preview Handlers
After successful integration, your preview handler should appear in the PowerToys settings UI under the `File Explorer Preview` Tab. In here you should be able to enable and disable your preview handler.
In the general settings of the Settings UI, you should be able to disable and enable all the preview handlers all at once.
