Hot Reload does not work on iOS when running from Mac

[ivmirx]

Description

I'm testing Hot Reload for a sample .NET 9 iOS app on macOS. Unfortunately, it does not work no matter what I try (simple method, timer-called method, timer-called Action)

Reproduction Steps

1. Download the project HotApple.zip
2. Run dotnet watch run --project HotApple/HotApple.csproj -f net9.0-ios /p:Platform=iPhoneSimulator /p:BuildIpa=false /p:MtouchFastDev=true /p:UseInterpreter=true
3. Change label!.Text = $"Tick: {tickCount}" to label!.Text = $"Test: {tickCount}"
4. See dotnet watch logging 🔥 [HotApple (net9.0-ios)] Hot reload succeeded.
5. The label text is not updated (aside from the running count)

Expected behavior

The label changes the text before the count

Actual behavior

The label only changes the count when the timer runs

Regression?

No response

Known Workarounds

No response

Configuration

• .NET 9.0.203
• macOS 15.4.1
• ARM64
• Xcode 16.3
• iOS 18.4 in Simulator

Other information

AppDelegate.cs:

namespace HotApple;

[Register ("AppDelegate")]
public class AppDelegate : UIApplicationDelegate {
	public override UIWindow? Window { get; set; }

	public override bool FinishedLaunching(UIApplication app, NSDictionary? launchOptions)
    {
        Window = new UIWindow(UIScreen.MainScreen.Bounds);
        Window.RootViewController = new TimerViewController();
        Window.MakeKeyAndVisible();
        return true;
    }
}

namespace HotApple;

public class TimerViewController : UIViewController
{
    UILabel? label;
    NSTimer? timer;
    int tickCount = 0;

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        View.BackgroundColor = UIColor.SystemBackground;

        label = new UILabel(View.Bounds)
        {
            TextAlignment = UITextAlignment.Center,
            AutoresizingMask = UIViewAutoresizing.All,
            Text = "Starting..."
        };

        View.AddSubview(label);

        Action updateText = () =>
        {
            tickCount++;
            label!.Text = $"Tick: {tickCount}";
        };

        timer = NSTimer.CreateRepeatingScheduledTimer(1.0, _ => updateText());
    }
}

[thaystg]

Hi!
I'm not sure if I understand the problem.
I think the behavior that you are getting is the expected behavior.

Action updateText = () =>
        {
            tickCount++;
            label!.Text = $"Tick: {tickCount}";
        };

Action updateText = () =>
        {
            tickCount++;
            label!.Text = $"Test: {tickCount}";
        };

When you change the code of the Action updateText, the new version of this code will only be executed the next time that the Action is executed, so it will be happen together with the tickCount++ during the next execution.

Also it important to say that there is a limitation on Mono Runtime. If you change a method body and you are executing it, the new method body will only be executed the next time that this method is executed, if you are in a loop inside the method, the new method body will never take effect and this is expected.

Please let us know if we missed something and didn't understand the problem correctly.

[ivmirx]

Hi Thays, thank you for looking at this!

the new version of this code will only be executed the next time that the Action is executed, so it will be happen together with the tickCount++ during the next execution

Yes, but in my case it's not happening after new calls. The timer counter updates, but the text I change from the editor never appears. That's why I added the timer in the first place: to see if I can trigger a reload on new Action calls (I tried regular methods too).

Is there any template project I can try out?