How to decompile XAP file

Decompiling an XAP file (a Windows Phone app package) into C# code and rebuilding it into a new XAP is a multi-step process.

Steps

Step 1: Extract the Contents of the XAP File

1. Rename the XAP file:
   • Change the .xap file extension to .zip.
   • Extract the ZIP file using any archive tool (e.g., WinRAR, 7-Zip).
2. Analyze the Contents:
   • Look for the DLL files in the Bin or App folders. These contain the compiled C# code.
   • Other assets, such as XAML, images, and configuration files, will also be extracted.

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Step 2: Decompile the DLL Files

1. Use a Decompiler:
   • Tools like ILSpy, dnSpy, or Telerik JustDecompile can be used to decompile .dll files to readable C# code.
2. Steps for Decompilation:
   • Open the .dll file in the decompiler.
   • Explore the namespaces, classes, and methods to understand the code structure.
   • Export the decompiled code to a Visual Studio project (most decompilers have this feature).
3. Analyze Decompiled Code:
   • Review the decompiled code for errors or incomplete segments caused by obfuscation.
   • Manually reconstruct missing parts if necessary.

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Step 3: Modify the Decompiled Code (Optional)

1. Open the exported Visual Studio project.
2. Make any necessary changes to the code.
   • Fix errors caused by obfuscation or incompatible constructs.
   • Modify functionality, if required.

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Step 4: Rebuild the XAP File

1. Create a New Windows Phone Project:
   • In Visual Studio, create a new Windows Phone project of the same version (e.g., Windows Phone 8.0, 8.1).
   • Use the same name and namespace as the original project (if possible).
2. Add Decompiled Code and Assets:
   • Add the decompiled code and assets (images, XAML files, etc.) to the project.
   • Ensure the AppManifest.xaml file matches the original app's configuration.
3. Fix Dependencies:
   • Reference required libraries (.dll) that were part of the original app or are available in the Windows Phone SDK.
4. Build the Project:
   • Set the project to build as a Windows Phone app.
   • Compile the project in Visual Studio to generate a new XAP file.

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Step 5: Test the New XAP File

1. Deploy the new XAP to a Windows Phone emulator or device.
   • Use tools like the Windows Phone Application Deployment tool (available in the Windows Phone SDK).
2. Test for functionality and stability.

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Additional Notes

• Legal Considerations: Decompiling and modifying software without explicit permission may violate copyright or licensing agreements.
• Obfuscation: If the original XAP was obfuscated, the decompiled code may not be fully readable or functional, requiring significant effort to reconstruct.
• Re-signing the App: The new XAP must be signed with a valid certificate for deployment.

How to reuse .xnb files

1. Extract and place them into the rebuilt project’s Content folder.
2. Match the original folder structure and paths.
3. Set them to Content build action in the IDE.
4. Optionally edit them by decompiling and recompiling using the XNA or MonoGame Pipeline tools.