HotReload.md

Hot Reload

This document explains the opt-in Hot Reload flow for MewUI apps using C# markup. Hot Reload rebuilds window content by re-running a registered build callback.

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1. Enable Hot Reload (app assembly)

Add a MetadataUpdateHandler in your app assembly (DEBUG only):

#if DEBUG
[assembly: System.Reflection.Metadata.MetadataUpdateHandler(
    typeof(Aprillz.MewUI.HotReload.MewUiMetadataUpdateHandler))]
#endif

You can place this in Program.cs or a dedicated AssemblyInfo.cs.

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2. Register a build callback

Hot Reload only rebuilds windows that have a build callback. The C# markup helper OnBuild(...) sets it and also runs the initial build.

var window = new Window()
    .OnBuild(w =>
    {
        w.Title("Hot Reload Demo");
        w.Content(new StackPanel()
            .Spacing(8)
            .Children(
                new TextBlock().Text("Edit code and Hot Reload."),
                new Button().Content("Click")
            ));
    });

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3. Full example

#if DEBUG
[assembly: System.Reflection.Metadata.MetadataUpdateHandler(
    typeof(Aprillz.MewUI.HotReload.MewUiMetadataUpdateHandler))]
#endif

using Aprillz.MewUI;
using Aprillz.MewUI.Markup;
using Aprillz.MewUI.Controls;

// 1) Register a build callback (DateTime updates after code change + Hot Reload)
var window = new Window()
    .OnBuild(w => w
        .Title("Hot Reload Demo")
        .Content(new StackPanel()
            .Spacing(8)
            .Children(
                new TextBlock().Text($"Now: {DateTime.Now}"),
                new Button().Content("Click")
            )));

// 2) Select platform/backend and run
Application.Create()
    .UseWin32()
    .UseDirect2D()
    .Run(window);

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4. Notes

• Hot Reload is opt-in. No build callback = no reload.
• The rebuild runs on the UI thread and simply re-invokes your build callback.
• Preserve state in your own view-model or services if needed.
• Hot Reload is not supported on NativeAOT.
• You can trigger a rebuild manually via MewUiHotReload.RequestReload().