UE4 中委托与任务系统实践

1. 委托机制

委托机制是 UE4 提供的一种强大的功能，允许我们将函数的执行权转移给其他组件或对象。这种机制在游戏开发中非常有用，尤其是在需要扩展或模块化代码时。

1.1 委托类型

委托可以分为多种类型，包括：

Object：直接使用 UObject 的成员函数

Lambda：使用 lambda 表达式

Raw：直接使用函数指针

SP：静态函数

Static：静态成员函数

WeakLambda：弱引用 lambda

UFunction：通过 UFunction 类绑定的函数

1.2 委托执行

void UDelegateObject::TestDelegate() {    UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__));}

1.3 委托绑定与管理

FTestDelegate& UDelegateMaker::MakeDelegate(EDelegateType Type) {    if (Delegate.IsBound()) {        Delegate.Unbind();    }    switch (Type) {        case EDelegateType::Object:            if (UEObject == nullptr) {                UEObject = NewObject
   
    ();            }            Delegate.BindUObject(UEObject, &UDelegateObject::TestDelegate);            break;    }}

void ADelegateInvoker::InvokeDelegate(EDelegateType Type) {    if (Maker == nullptr) {        Maker = NewObject
   
    ();        Maker->MakeDelegate(Type).ExecuteIfBound();    } else {        Maker->MakeDelegate(Type).ExecuteIfBound();    }}

2. 多线程

多线程编程在游戏开发中非常重要，尤其是在需要同时处理复杂任务时。UE4 提供了丰富的多线程支持工具和功能。

3. 依赖关系结构体

依赖关系结构体用于定义任务之间的依赖关系，确保任务按正确顺序执行。

USTRUCT(BlueprintType) struct FMyTaskItem {    GENERATED_USTRUCT_BODY()public:    UPROPERTY(BlueprintReadWrite)    FString TaskName;    FString TaskName;    FGraphEventRef GraphEvent;    TGraphTask* GraphTask;    FMyTaskItem() :        TaskName(TEXT("NoName")),        GraphEvent(nullptr),        GraphTask(nullptr) {}    FMyTaskItem(FString Name, FGraphEventRef EventRef = FGraphEventRef())        : TaskName(Name),        GraphEvent(EventRef),        GraphTask(nullptr) {}    FMyTaskItem(FString Name, TGraphTask* Task = nullptr)        : TaskName(Name),        GraphEvent(nullptr),        GraphTask(Task) {}    ~FMyTaskItem() {        GraphEvent = nullptr;    }};

4. 任务定义

任务类用于定义任务的具体行为和执行方式。

class FJustPrintTask {    FString TaskName;    TArray
   
        ChildEvents;    AActor* TaskOwner;public:    FJustPrintTask(FString Name, TArray
    
         Events, AActor* Actor) :        TaskName(Name),        ChildEvents(Events),        TaskOwner(Actor) {}    ~FJustPrintTask() {}    FORCEINLINE TStatId GetStatId() const {        RETURN_QUICK_DECLARE_CYCLE_STAT(FJustPrintTask, STATGROUP_TaskGraphTasks);    }    static ENamedThreads::Type GetDesiredThread() {        return ENamedThreads::AnyThread;    }    static ESubsequentsMode::Type GetSubsequentsMode() {        return ESubsequentsMode::TrackSubsequents;    }    void DoTask(ENamedThreads::Type CurrentThread, const FGraphEventRef& MyCompletionGraphEvent) {        UE_LOG(LogTemp, Log, TEXT(__FUNCTION__ " %s:Begin"), *TaskName);        for (TGraphTask* Task : ChildEvents) {            if (Task) {                Task->Unlock();                MyCompletionGraphEvent->DontCompleteUntil(Task->GetCompletionEvent());            }        }        MyCompletionGraphEvent->DontCompleteUntil(TGraphTask::CreateTask().ConstructAndDispatchWhenReady(TaskName, TaskOwner));        UE_LOG(LogTemp, Log, TEXT(__FUNCTION__ " %s:End"), *TaskName);    }}

5. 报告任务

报告任务用于在任务完成时触发特定事件。

class FReportTask {    FString TaskName;    AActor* TaskOwner;public:    FReportTask(FString Name, AActor* Actor) :        TaskName(Name),        TaskOwner(Actor) {}    ~FReportTask() {}    FORCEINLINE TStatId GetStatId() const {        RETURN_QUICK_DECLARE_CYCLE_STAT(FReportTask, STATGROUP_TaskGraphTasks);    }    static ENamedThreads::Type GetDesiredThread() {        return ENamedThreads::GameThread;    }    static ESubsequentsMode::Type GetSubsequentsMode() {        return ESubsequentsMode::TrackSubsequents;    }    void DoTask(ENamedThreads::Type CurrentThread, const FGraphEventRef& MyCompletionGraphEvent) {        AMyTaskGraphActor* Actor = Cast
   
    (TaskOwner);        if (IsValid(Actor)) {            Actor->OnTaskComplete(TaskName);        }    }}

6. Actor 与蓝图类

Actor 类用于管理任务执行。

UCLASS() class UECPP_API AMyTaskGraphActor : public AActor {    GENERATED_BODY()public:    AMyTaskGraphActor();    FMyTaskItem CreateTask(FString TaskName, const TArray
   
    & Prerequisites, const TArray
    
     & ChildTasks, bool DispatchWhenReady = true);    FMyTaskItem CreateTaskPure(FString TaskName, bool DispatchWhenReady = true) {        return CreateTask(TaskName, Empty, Empty, DispatchWhenReady);    }    FMyTaskItem CreateTaskWithPrerequisitesOnly(FString TaskName, const TArray
     
      & Prerequisites, bool DispatchWhenReady = true) {        return CreateTask(TaskName, Prerequisites, Empty, DispatchWhenReady);    }    FMyTaskItem CreateTaskWithChildTasksOnly(FString TaskName, const TArray
      
       & ChildTasks, bool DispatchWhenReady = true) {        return CreateTask(TaskName, Empty, ChildTasks, DispatchWhenReady);    }    UFUNCTION(BlueprintCallable)    void FireTask(const FMyTaskItem& Task);    UFUNCTION(BlueprintImplementableEvent)    void OnTaskComplete(const FString& TaskName);}

7. 任务执行

任务执行需要按照依赖关系顺序完成。

void FJustPrintTask::DoTask(ENamedThreads::Type CurrentThread, const FGraphEventRef& MyCompletionGraphEvent) {    UE_LOG(LogTemp, Log, TEXT(__FUNCTION__ " %s:Begin"), *TaskName);    for (TGraphTask* Task : ChildEvents) {        if (Task) {            Task->Unlock();            MyCompletionGraphEvent->DontCompleteUntil(Task->GetCompletionEvent());        }    }    MyCompletionGraphEvent->DontCompleteUntil(TGraphTask::CreateTask().ConstructAndDispatchWhenReady(TaskName, TaskOwner));    UE_LOG(LogTemp, Log, TEXT(__FUNCTION__ " %s:End"), *TaskName);}

8. Actor 函数实现

void AMyTaskGraphActor::FireTask(const FMyTaskItem& Task) {    if (Task.GraphTask) {        UE_LOG(LogTemp, Log, TEXT("Task[%s] Fire."), *Task.TaskName));        Task.GraphTask->Unlock();    }}

通过以上内容，可以看出 UE4 提供了强大的任务和委托系统，能够有效管理复杂任务流程和依赖关系。

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