Maui Hot Reload Diagnostics

.NET MAUI Hot Reload Diagnostics

Systematically diagnose Hot Reload failures for .NET MAUI apps.

Quick Diagnosis Checklist

1. Identify what's failing: XAML Hot Reload (.xaml changes) vs C# Hot Reload (.cs changes)
2. Check run configuration: Must be Debug config, started with F5/debugger attached
3. Save file and re-execute code path: C# changes require re-triggering the code
4. Check Hot Reload output: View > Output > "Hot Reload" (VS) or "C# Hot Reload" (VS Code)

Environment Variables for Diagnostics

Enable detailed logging

# Mac/Linux - Edit and Continue logs
export Microsoft_CodeAnalysis_EditAndContinue_LogDir=/tmp/HotReloadLog

# Windows
set Microsoft_CodeAnalysis_EditAndContinue_LogDir=%temp%\HotReloadLog

# XAML Hot Reload logging
export HOTRELOAD_XAML_LOG_MESSAGES=1

# Xamarin-style debug logging (legacy, may help)
export XAMARIN_HOT_RELOAD_SHOW_DEBUG_LOGGING=1

Check if variables are set

# Mac/Linux
env | grep -i hotreload
env | grep -i EditAndContinue

# Windows PowerShell
Get-ChildItem Env: | Where-Object { $_.Name -match "hotreload|EditAndContinue" }

File Encoding Requirement

CRITICAL: All .cs files must be UTF-8 with BOM encoding.

Check encoding

# Check if file has BOM (should show "UTF-8 Unicode (with BOM)")
file -I *.cs

# Find files without BOM
find . -name "*.cs" -exec sh -c 'head -c 3 "$1" | od -An -tx1 | grep -q "ef bb bf" || echo "$1"' _ {} \;

Fix encoding (convert to UTF-8 with BOM)

# Single file
sed -i '1s/^\(\xef\xbb\xbf\)\?/\xef\xbb\xbf/' file.cs

# Or use VS Code: Open file > Save with Encoding > UTF-8 with BOM

VS Code Settings

Enable in VS Code settings (search "Hot Reload"):

{
  "csharp.experimental.debug.hotReload": true,
  "csharp.debug.hotReloadOnSave": true,
  "csharp.debug.hotReloadVerbosity": "detailed"
}

Visual Studio Settings

1. Tools > Options > Debugging > .NET/C++ Hot Reload
2. Enable: Enable Hot Reload, Apply on file save
3. Set Logging verbosity to Detailed or Diagnostic

MetadataUpdateHandler

For custom hot reload handling (e.g., MauiReactor), implement MetadataUpdateHandler:

[assembly: System.Reflection.Metadata.MetadataUpdateHandler(typeof(HotReloadService))]

internal static class HotReloadService
{
    // Called when hot reload clears cached metadata
    public static void ClearCache(Type[]? updatedTypes) { }
    
    // Called after hot reload updates are applied
    public static void UpdateApplication(Type[]? updatedTypes)
    {
        // Trigger UI refresh here
        MainThread.BeginInvokeOnMainThread(() =>
        {
            // Refresh your UI framework
        });
    }
}

Verify MetadataUpdateHandler is registered

# Search for handler in codebase
grep -rn "MetadataUpdateHandler" --include="*.cs"

# Check assembly attributes
grep -rn "assembly:.*MetadataUpdateHandler" --include="*.cs"

MauiReactor-Specific Hot Reload

MauiReactor v3+ uses .NET's feature switch pattern for hot reload (no code call needed).

Setup (MauiReactor v3+)

Add to your .csproj file:

<ItemGroup Condition="'$(Configuration)'=='Debug'">
  <RuntimeHostConfigurationOption Include="MauiReactor.HotReload" Value="true" Trim="false" />
</ItemGroup>

<!-- For Release builds (AOT compatibility) -->
<ItemGroup Condition="'$(Configuration)'=='Release'">
  <RuntimeHostConfigurationOption Include="MauiReactor.HotReload" Value="false" Trim="true" />
</ItemGroup>

Note: If migrating from MauiReactor v2, remove the EnableMauiReactorHotReload() call from MauiProgram.cs.

Check MauiReactor hot reload setup

# Verify RuntimeHostConfigurationOption in csproj
grep -A2 "MauiReactor.HotReload" *.csproj

# Ensure EnableMauiReactorHotReload is NOT present (v3+)
grep -rn "EnableMauiReactorHotReload" --include="*.cs" && echo "WARNING: Remove this call for v3+"

MauiReactor hot reload requirements

1. RuntimeHostConfigurationOption set in .csproj (not a code call)
2. Debug configuration
3. Debugger attached (F5)
4. Works on all platforms (iOS, Android, Mac Catalyst, Windows)
5. Works in VS Code and Visual Studio

C# Markup (CommunityToolkit.Maui.Markup) Hot Reload

C# Markup apps need the ICommunityToolkitHotReloadHandler to refresh UI on hot reload.

Setup

1. Add the NuGet package: CommunityToolkit.Maui.Markup

2. Enable in MauiProgram.cs:

var builder = MauiApp.CreateBuilder();
builder
    .UseMauiApp<App>()
    .UseMauiCommunityToolkitMarkup(); // Enables hot reload support

3. Implement the handler interface on pages/views that need refresh:

public partial class MainPage : ContentPage, ICommunityToolkitHotReloadHandler
{
    public MainPage()
    {
        Build();
    }

    void Build() => Content = new VerticalStackLayout
    {
        Children = 
        {
            new Label().Text("Hello, World!"),
            new Button().Text("Click Me")
        }
    };

    // Called by hot reload - rebuild UI
    void ICommunityToolkitHotReloadHandler.OnHotReload() => Build();
}

Check C# Markup hot reload setup

# Verify package reference
grep -i "CommunityToolkit.Maui.Markup" *.csproj

# Check for UseMauiCommunityToolkitMarkup in MauiProgram.cs
grep -n "UseMauiCommunityToolkitMarkup" MauiProgram.cs

# Find classes implementing ICommunityToolkitHotReloadHandler
grep -rn "ICommunityToolkitHotReloadHandler" --include="*.cs"

Key points for C# Markup hot reload

• Extract UI building into a separate Build() method
• Implement ICommunityToolkitHotReloadHandler on any page/view needing refresh
• The OnHotReload() method is called automatically after C# hot reload
• Works alongside standard C# Hot Reload (method body changes)

Blazor Hybrid Hot Reload

Blazor Hybrid apps in MAUI have their own hot reload behavior for .razor and .css files.

How Blazor Hybrid hot reload works

• Razor components (.razor): Changes to markup and C# code blocks reload automatically
• CSS files (.css): Style changes apply immediately
• C# code-behind (.razor.cs): Uses standard C# Hot Reload rules
• Shared C# code: Standard C# Hot Reload applies

Setup requirements

1. Debug configuration (not Release)
2. Debugger attached (F5, not Ctrl+F5)
3. For Visual Studio: Ensure "Hot Reload on File Save" is enabled

Check Blazor Hybrid setup

# Verify BlazorWebView is configured
grep -rn "BlazorWebView" --include="*.xaml" --include="*.cs"

# Check for _Imports.razor
find . -name "_Imports.razor"

# Verify wwwroot exists
ls -la */wwwroot/ 2>/dev/null || ls -la wwwroot/ 2>/dev/null

Blazor Hybrid hot reload limitations

• Adding new components: May require restart
• Changing component parameters: Usually works
• Modifying @inject services: May require restart
• Static asset changes (images, fonts): Require restart
• Changes to Program.cs or MauiProgram.cs: Always require restart

Troubleshooting Blazor Hybrid

1. Razor changes not applying:

   • Ensure file is saved
   • Check browser dev tools console (if available) for errors
   • Verify the component is actually being rendered

2. CSS changes not applying:

   • Hard refresh may be needed (changes cached)
   • Check CSS isolation (.razor.css) is properly linked

3. Partial updates / flickering:

   • This is normal for Blazor's diff-based rendering
   • State may reset if component re-initializes

Environment variable for Blazor debugging

# Enable detailed Blazor logging
export ASPNETCORE_ENVIRONMENT=Development

Common Issues and Fixes

Issue: "Nothing happens when I save"

1. Verify Debug configuration (not Release)
2. Check Hot Reload output for errors
3. Ensure file is saved (not just modified)
4. Re-execute the code path (navigate again, tap button again)

Issue: "Unsupported edit" / "Rude edit"

Some changes require app restart:

• Adding/removing methods, fields, properties
• Changing method signatures
• Modifying static constructors
• Changes to generics

Issue: XAML changes don't apply (iOS)

• Set Linker to Don't Link in iOS build settings
• Config must be named exactly Debug
• Don't use XamlCompilationOptions.Skip

Issue: Changes apply but UI doesn't update

• For C#: Must re-trigger the code (re-navigate, re-tap)
• Check for cached binding values or state
• Verify you're editing the correct target framework file

Diagnostic Commands

Collect full diagnostic bundle

# 1. Environment info
dotnet --info > dotnet-info.txt
dotnet workload list > workloads.txt

# 2. Build with binary log
dotnet build -bl:build.binlog -c Debug

# 3. Check for encoding issues
find . -name "*.cs" -path "*/src/*" | head -20 | xargs file

# 4. Check hot reload env vars
env | grep -iE "(hotreload|editandcontinue|xamarin.*debug)" || echo "No hot reload env vars set"

Enable all diagnostic logging then reproduce

export Microsoft_CodeAnalysis_EditAndContinue_LogDir=/tmp/HotReloadLog
export HOTRELOAD_XAML_LOG_MESSAGES=1
# Launch IDE from this terminal, reproduce issue, then check /tmp/HotReloadLog/

References

• Diagnosing Hot Reload (MAUI Wiki)
• .NET Hot Reload in Visual Studio
• Supported code changes (C#)
• XAML Hot Reload for .NET MAUI
• CommunityToolkit.Maui.Markup Hot Reload
• Blazor Hybrid with .NET MAUI