虚幻引擎 4：如何将委托传递给异步线路跟踪？答案

【问题标题】：Unreal Engine 4: How to pass a delegate into an async line trace?虚幻引擎 4：如何将委托传递给异步线路跟踪？
【发布时间】：2021-04-08 16:39:37
【问题描述】：

我正在尝试在虚幻中追踪很多行，我目前正在使用LineTraceSingleByChannel（来自不同的同时线程）执行此操作。但是，我试图切换到AsyncLineTraceByChannel，我想在其中使用FTraceDelegate 在完成时调用函数。我似乎在编译时遇到错误，但我无法找出原因。错误点在第 571 行，这是 FTraceDelegate 的右括号所在的位置（我在代码中对此进行了标记）。

我做错了什么，我该如何解决？

导致错误的代码：

FTraceHandle UAirBlueprintLib::GetObstacleAdvAsync(const AActor* actor, const FVector& start, const FVector& end,
    FHitResult& hit, TArray<AActor*>& ignore_actors, ECollisionChannel collision_channel, bool trace_complex, bool get_material)
{
    bool bIgnoreSelf = false;
    FName traceTag;
    FTraceDelegate traceDelegate = FTraceDelegate::CreateWeakLambda(actor, [](const FTraceHandle& handle, FTraceDatum& data)
    {
        //My logic goes here;
        if (data.OutHits.Num() > 0)
        {
            const FHitResult& Result = data.OutHits[0];
        }
    });

    FCollisionQueryParams trace_params;
    trace_params.bReturnPhysicalMaterial = get_material;
    trace_params.bTraceComplex = trace_complex;
    trace_params.AddIgnoredActors(ignore_actors);

    return actor->GetWorld()->AsyncLineTraceByChannel(EAsyncTraceType::Single,
        start, end,
        collision_channel,
        trace_params,
        FCollisionResponseParams::DefaultResponseParam,
        &traceDelegate);
}

错误：

1>c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateInstancesImpl.h(1008): error C2440: 'return': cannot convert from 'T *' to 'UObject *'
1>          with
1>          [
1>              T=const AActor
1>          ]
1>  c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateInstancesImpl.h(1008): note: Conversion loses qualifiers
1>  c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateInstancesImpl.h(1007): note: while compiling class template member function 'UObject *TWeakBaseFunctorDelegateInstance<UserClass,TTypeWrapper<void> (const FTraceHandle &,FTraceDatum &),FunctorType>::GetUObject(void) const'
1>          with
1>          [
1>              UserClass=const AActor,
1>              FunctorType=UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>
1>          ]
1>  c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateInstancesImpl.h(1019): note: see reference to function template instantiation 'UObject *TWeakBaseFunctorDelegateInstance<UserClass,TTypeWrapper<void> (const FTraceHandle &,FTraceDatum &),FunctorType>::GetUObject(void) const' being compiled
1>          with
1>          [
1>              UserClass=const AActor,
1>              FunctorType=UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>
1>          ]
1>  c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateInstancesImpl.h(1084): note: see reference to class template instantiation 'TWeakBaseFunctorDelegateInstance<UserClass,TTypeWrapper<void> (const FTraceHandle &,FTraceDatum &),FunctorType>' being compiled
1>          with
1>          [
1>              UserClass=const AActor,
1>              FunctorType=UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>
1>          ]
1>  c:\<redacted>\unrealengine\engine\source\runtime\core\public\Delegates/DelegateSignatureImpl.inl(146): note: see reference to class template instantiation 'TWeakBaseFunctorDelegateInstance<UserClass,void (const FTraceHandle &,FTraceDatum &),UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>>' being compiled
1>          with
1>          [
1>              UserClass=const AActor
1>          ]
1>  C:\<redacted>\Documenten\<redacted>\Unreal\Environments\<redacted>\Plugins\<redacted>\Source\AirBlueprintLib.cpp(571): note: see reference to function template instantiation 'TBaseDelegate<void,const FTraceHandle &,FTraceDatum &> TBaseDelegate<TTypeWrapper<void>,const FTraceHandle &,FTraceDatum &>::CreateWeakLambda<const AActor,UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>,>(UserClass *,FunctorType &&)' being compiled
1>          with
1>          [
1>              UserClass=const AActor,
1>              FunctorType=UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>
1>          ]
1>  C:\<redacted>\Documenten\<redacted>\Unreal\Environments\<redacted>\Plugins\<redacted>\Source\AirBlueprintLib.cpp(564): note: see reference to function template instantiation 'TBaseDelegate<void,const FTraceHandle &,FTraceDatum &> TBaseDelegate<TTypeWrapper<void>,const FTraceHandle &,FTraceDatum &>::CreateWeakLambda<const AActor,UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>,>(UserClass *,FunctorType &&)' being compiled
1>          with
1>          [
1>              UserClass=const AActor,
1>              FunctorType=UAirBlueprintLib::GetObstacleAdvAsync::<lambda_628e4b4604e5c1758c2bd3d199f08ff6>
1>          ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\VC\VCTargets\Microsoft.MakeFile.Targets(44,5): error MSB3075: The command "C:\<redacted>\UnrealEngine\Engine\Build\BatchFiles\Build.bat -Target="ShaderCompileWorker Win64 Development" -Target="<redacted> Win64 Development -Project=\"C:\<redacted_path>"" -WaitMutex -FromMsBuild" exited with code 5. Please verify that you have sufficient rights to run this command.

【问题讨论】：

听起来你在某处缺少#include，可能是#include "GameFramework/Actor.h"
感谢您的意见！我尝试了一些不同的包含但没有任何成功。不过，切换到 BindLambda 对我有用。
哦，好的，谢谢你告诉我！

标签： c++ unreal-engine4

【解决方案1】：

我改用了一种稍微不同的方法来解决问题。如下创建委托对我有用：

FTraceDelegate traceDelegate;
traceDelegate.BindLambda([](const FTraceHandle& handle, FTraceDatum& data)
    {
        DrawDebugPoint(data.PhysWorld.Get(), data.End, 7.0f, FColor::Purple, false, 0.105);
        if (data.OutHits.Num() > 0)
        {
            const FHitResult& Result = data.OutHits[0];
        }
    });

【讨论】：