Crashing, Debugging & Build Errors in .NET MAUI (.NET 9)? Read This First!

Top 5 Common .NET MAUI (.NET 9) Issues and Developer-Approved Solutions

Working with .NET MAUI on .NET 9 can be exciting but challenging. Many developers face recurring issues that may not be well documented. Here are 5 common problems and their proven solutions with references for further help.

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1. 🧩 HybridWebView JavaScript Callback Problems

Issue: Calling JavaScript using InvokeJavaScriptAsync<T>() without returning a value can throw exceptions.

Solution: Ensure your JavaScript functions return serialized values explicitly.

JavaScript Example:

function setBackground() {
    document.body.style.backgroundColor = getRandomHexColor();
    return JSON.stringify("ok");
}
    

C# Call:

await myWebView.InvokeJavaScriptAsync<string>("setBackground", new object[] { });
    

Source: GitHub Issue #25804

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2. 🐞 Android Debugger Crash on Launch

Issue: The debugger sometimes crashes when launching the app on Android with .NET 9.

Solution:

• Update Visual Studio and Android SDKs
• Restart ADB and clean the deployment
• Try deploying without debugger, then attach it manually

Source: Stackoverflow Issue

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Table of Contents for .Net Maui

• What is .NET MAUI and why it’s important
• Applying the MVVM pattern for cleaner architecture
• Working with Renderers and Mappers
• Storing data locally using SQLite and Preferences
• Image Picker from gallery
• Sending push notifications using Firebase
• Publishing your app to Android and iOS stores
• 🌟 Explore More Topics

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3. 🛠 Platform Version Isn’t Present Error

Issue: Build error such as:

"Platform version is not present for net9.0-android, net9.0-ios…"

Solution:

• Uninstall x86 .NET SDK
• Ensure x64 is first in your PATH environment variable
• Reinstall workloads:

dotnet workload install maui
    

Sources: GitHub #25767, Telerik Blog

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4. ⚠️ Xcode or Command-Line Tools Not Found (Mac)

Issue: Errors on macOS saying Xcode or CLI tools not installed (even after installation).

Solution:

• Install full Xcode via the App Store
• Set Xcode CLI path: Xcode > Preferences > Locations > Command Line Tools
• Restart Visual Studio for Mac

Sources: Telerik Blog, Official Docs

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5. 🔄 Upgrade from .NET 8 to 9 Causing Crashes

Issue: App crashes on launch after migrating from .NET MAUI 8 to 9.

Solution:

• Delete bin and obj folders
• Update all NuGet packages to 9.x versions
• Match iOS/macOS deployment targets with .NET 9's requirements
• Rebuild and redeploy

Source: Telerik Blog

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Summary Table

Issue	Root Cause	Solution
HybridWebView JS errors	Missing return values	Use explicit JSON return and correct C# overload
Debugger crash on Android	Toolchain/device instability	Update SDKs, clean device, reattach debugger
Platform version not found	x86 SDK conflict	Prioritize x64 SDK and reinstall workloads
Xcode not found	CLI tools not configured	Set Xcode CLI path properly
Upgrade crashes	Mixed SDKs, target mismatch	Clean rebuild, update targets and packages

If you're working on a .NET MAUI app and face any of these issues, try the above solutions or check the referenced GitHub issues and docs for real-time updates from the developer community.