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Hot reload not working sometimes

Hello Unreal community. I made plugin (just few simple classes) and use it in my project. Everything works fine, but i can't compile in Visual Studio when Editor is running. In VS i see error message:

 Compiling game modules for hot reload
 2>  Performing 4 actions (4 in parallel)
 2>  [2/4] Link UE4Editor-MyPluginRuntime-5769.lib
 2>     Creating library D:\Unreal\TestProject\Plugins\MyPluginRuntime\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-MyPluginRuntime-5769.lib and object D:\Unreal\TestProject\Plugins\MyPluginRuntime\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-MyPluginRuntime-5769.exp
 2>  TestProjectGameMode.cpp
 2>  [3/4] Link UE4Editor-TestProject-8983.dll
 2>  [4/4] Link UE4Editor-TestProject-7949.lib
 2>     Creating library D:\Unreal\TestProject\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-TestProject-8983.lib and object D:\Unreal\TestProject\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-TestProject-8983.exp
 2>     Creating library D:\Unreal\TestProject\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-TestProject-8983.suppressed.lib and object D:\Unreal\TestProject\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-TestProject-8983.suppressed.exp
 2>ERROR : UBT error : Failed to produce item: D:\Unreal\TestProject\Intermediate\Build\Win64\UE4Editor\Development\UE4Editor-TestProject-7949.lib

And in Editor:

 LogModuleManager:Warning: ModuleManager: Unable to load module 'D:/Unreal/TestProject/Binaries/Win64/UE4Editor-TestProject-8983.dll' because the file couldn't be loaded by the OS.
 Warning: HotReload failed, reload failed /Script/TestProject.

But if i'm compiling in Editor, no errors and hot reload is working as usual.

Maybe i'm doing something wrong? Please help me.

Product Version: UE 4.15
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asked Mar 05 '17 at 08:59 PM in Bug Reports

iLef gravatar image

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Hey iLef-

Your post mentions you're unable to compile in Visual Studio but then says you can compile in the editor with no errors. Just to make sure I understand correctly, you're saying that when you compile in VS you get a message that hot reload did not complete, but you do not get this message if you compile in the project itself? If this is the case, this is a known "false positive" that VS is reporting, and the hot reload is actually completing successfully: https://issues.unrealengine.com/issue/UE-42205 . If your issue is something different, please elaborate on your setup and reproduction steps to help me investigate the issue locally.


Doug Wilson

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answered Mar 06 '17 at 04:09 PM

Doug Wilson gravatar image

Doug Wilson ♦♦ STAFF
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iLef gravatar image iLef Mar 06 '17 at 11:07 PM

Hi Doug. Yes, you are right, this is my case. If you want, i can send sample project with this issue. Thanks for your help!

iLef gravatar image iLef 2 days ago

Unfortunately Hotfix 4.15.1 doesn't work for me. Yeah, false errors in VS now gone away, but hot reload still doesn't work. I get the same warning in Editor:

 LogModuleManager:Warning: ModuleManager: Unable to load module 'D:/Unreal/DbugVarsProject/Binaries/Win64/UE4Editor-DbugVarsProject-229.dll' because the file couldn't be loaded by the OS.
 Warning: HotReload failed, reload failed /Script/DbugVarsProject.

In attachment link text you can find my test project. Repro steps:

1)Generate VS project files

2)Open project in VS

3)Compile and launch project

4)Change something in code (for example log in GameMode)

5)Build solution

6)Now you can see warning in editor without any errors and hot reload didn't work

Doug Wilson gravatar image Doug Wilson ♦♦ STAFF yesterday

Hey iLef-

I apologize for missing it before, but with the sample project you provided I now understand what is happening here. I didn't understand that you are using a plugin and that is what is causing the problem. Plugin files are not included when a hot reload occurs, and the reason you're getting the error you are is because your GameModeBase.cpp file references your plugin. So when the game hot reloads, that file searches for a compatible hot reload of the plugin which doesn't exist.

iLef gravatar image iLef yesterday

Hey Doug, So there is no way how to make this work? And there is only one solution: move all code from plugin to my project?

Also i can't understand why when i compile in Editor everything works?

Doug Wilson gravatar image Doug Wilson ♦♦ STAFF yesterday

The editor compile completely ignores the plugin whereas VS fails when it tries to hot reload the plugin. You can also compile everything (game and plugin) by closing the editor and preforming a regular compile rather than a hot reload.

j_zeitler gravatar image j_zeitler 22 hours ago

I also have this problem, using a couple of plugins that are referenced in my project c++ code.

Do I understand this correctly; It's not possible to compile from VS and hot reload while having plugins referenced in project c++ code? I know I have been able to do this before but haven't been able to since the hot reload .lib issue

Doug Wilson gravatar image Doug Wilson ♦♦ STAFF 18 hours ago

You can compile, however changes to plugin code are not hot reloaded and won't be reflected in the editor. The issue in this specific case is the project code contains a reference to a delegate that is defined in the plugin.

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