Скачать или смотреть Solving the UE4 UserWidget Button issue: Spawning Actors from PlayerController

In this guide, learn how to resolve the issue of spawning actors in Unreal Engine 4 using a button in a UserWidget. We’ll guide you step-by-step through the entire process.
---
This video is based on the question https://stackoverflow.com/q/66605075/ asked by the user 'Marklar' ( https://stackoverflow.com/u/5608937/ ) and on the answer https://stackoverflow.com/a/66652192/ provided by the user 'Marklar' ( https://stackoverflow.com/u/5608937/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: UE4 UserWidget Button bind with spawning actor in PlayerController

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Spawning Actors in UE4 UserWidget Button Using PlayerController

As a developer working with Unreal Engine 4, you may encounter a situation where you want to spawn an actor using a button click event in a UserWidget. This task can turn tricky when there are access violations and the expected game behavior is not achieved. In this blog, we'll walk through a real coding issue and provide a solution to help you successfully link a button in a UserWidget to an actor spawn function in your PlayerController.

Understanding the Problem

In our case, the developer's goal was to click a button in MainUIWidget, which is a custom UserWidget, and spawn an actor from MyPlayerController. However, upon clicking the button, the function in MyPlayerController was crashing because GetWorld() was returning null, leading to access violations. The expected flow was:

The button in the widget is clicked.

A function in MyPlayerController is triggered.

An actor is spawned in the game world.

The Code Structure

The relevant classes and their structure were as follows:

MyPlayerController: Handles the player’s actions, including spawning actors.

MyGameHUD: A custom HUD that draws user interface elements.

MainUIWidget: The UserWidget containing the buttons.

Here’s a brief look at the critical snippets from MainUIWidget that were pertinent to the problem.

[[See Video to Reveal this Text or Code Snippet]]

The Solution

Moving the PlayerController Pointer Initialization

After analyzing the situation, the crux of the problem lay in when and where the PlayerControllerPtr was initialized. Initially, this was set in the UMainUIWidget constructor. However, this constructor runs before the widget is fully constructed, meaning there's a chance that GetOwningPlayer() may return an invalid reference at that time.

To fix this, the developer moved the initialization of PlayerControllerPtr from the constructor to the NativeBeginPlay() event, which runs after the widget is fully constructed and ready to interact with its parent classes. Here’s how the code now looks:

[[See Video to Reveal this Text or Code Snippet]]

How the Fixed Code Works Together

Initialization Backbone: By moving the pointer initialization to NativeConstruct, we ensured that PlayerControllerPtr is valid and can access GetWorld() successfully.

Button Click Signal: The button now correctly binds the click event to the signal function using AddDynamic. When the button is clicked, it launches SendSignalBuildBuildingBP_Button1, which calls ConstructBuilding.

Actor Spawning: In ConstructBuilding, we now have a proper reference to the MyPlayerController instance, allowing us to spawn the actor nicely without crashing.

Final Steps and Testing

With these changes in place, it's essential to test the functionality:

Click the Button: After your adjustments, run your project and click the button in the MainUIWidget.

Observe the Results: Ensure that the intended actor is spawned without any access violations.

Conclusion

By understanding how UMG widgets interact within UE4 and ensuring proper pointer initialization at the right time, we can effectively achieve the desired behavior. The essence of this fix highlights the importance of ensuring that object references are valid before using them, especially in complex engines like Unreal Engine 4.

If you're experiencing similar issues with spawning actors from a UserWidget, consider revising when and where you initialize your pointers. This method has been tried and tested, yielding improved results in UE4 projects. Happy coding!