ue-statetree-smartobjects

UE5 StateTree + SmartObjects 开发指南

一、StateTree 核心概念

StateTree 是 UE5 的层级状态机框架，结合行为树的选择器逻辑与传统状态机的状态/转换。

StateTree
├── State: Idle          ← 父状态（Selector 或 Sequence）
│   ├── Evaluator        ← 每帧更新共享数据（如感知结果）
│   ├── Task: WaitIdle   ← 执行具体行为
│   └── Transition → Patrol  [条件: !bEnemyVisible]
├── State: Patrol
│   ├── Task: MoveAlongPath
│   └── Transition → Chase   [条件: bEnemyVisible]
└── State: Chase
    ├── Task: MoveToTarget
    └── Transition → Attack   [条件: DistToTarget < 150]

关键类型

类型	基类	职责
Task	FStateTreeTaskBase	执行具体行为（移动、播放动画等）
Evaluator	FStateTreeEvaluatorBase	每帧更新共享上下文数据
Condition	FStateTreeConditionBase	转换条件判断
Schema	UStateTreeSchema	定义 StateTree 可访问的 Context 对象

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二、C++ Task 编写模板

最小 Task 骨架

// MyAITask.h
#pragma once
#include "StateTreeTaskBase.h"
#include "MyAITask.generated.h"

USTRUCT()
struct FMyAITaskInstanceData
{
    GENERATED_BODY()

    // 输入参数（在 StateTree 编辑器中绑定）
    UPROPERTY(EditAnywhere, Category = "Input")
    float Duration = 2.f;

    // 运行时状态
    float ElapsedTime = 0.f;
};

USTRUCT(DisplayName = "My AI Task")
struct FMyAITask : public FStateTreeTaskBase
{
    GENERATED_BODY()

    using FInstanceDataType = FMyAITaskInstanceData;

    virtual const UStruct* GetInstanceDataType() const override
    {
        return FMyAITaskInstanceData::StaticStruct();
    }

    virtual EStateTreeRunStatus EnterState(
        FStateTreeExecutionContext& Context,
        const FStateTreeTransitionResult& Transition) const override;

    virtual EStateTreeRunStatus Tick(
        FStateTreeExecutionContext& Context,
        const float DeltaTime) const override;

    virtual void ExitState(
        FStateTreeExecutionContext& Context,
        const FStateTreeTransitionResult& Transition) const override;
};

// MyAITask.cpp
#include "MyAITask.h"

EStateTreeRunStatus FMyAITask::EnterState(
    FStateTreeExecutionContext& Context,
    const FStateTreeTransitionResult& Transition) const
{
    FMyAITaskInstanceData& Data = Context.GetInstanceData(*this);
    Data.ElapsedTime = 0.f;
    return EStateTreeRunStatus::Running;
}

EStateTreeRunStatus FMyAITask::Tick(
    FStateTreeExecutionContext& Context,
    const float DeltaTime) const
{
    FMyAITaskInstanceData& Data = Context.GetInstanceData(*this);
    Data.ElapsedTime += DeltaTime;

    if (Data.ElapsedTime >= Data.Duration)
    {
        return EStateTreeRunStatus::Succeeded;
    }
    return EStateTreeRunStatus::Running;
}

void FMyAITask::ExitState(
    FStateTreeExecutionContext& Context,
    const FStateTreeTransitionResult& Transition) const
{
    // 清理资源
}