111 lines
3.8 KiB
Markdown
111 lines
3.8 KiB
Markdown
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# ExposedAsyncProxy
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- **功能描述：** 在 Async Task 节点中公开此类的一个代理对象。
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- **使用位置：** UCLASS
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- **引擎模块：** Blueprint
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- **元数据类型：** string="abc"
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- **限制类型：** Async Blueprint node
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- **关联项：** [HideSpawnParms](../Param/HideSpawnParms/HideSpawnParms.md), [HasDedicatedAsyncNode](../HasDedicatedAsyncNode/HasDedicatedAsyncNode.md), [HideThen](../HideThen/HideThen.md)
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- **常用程度：** ★★★
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在UK2Node_BaseAsyncTask中使用，用来为蓝图异步节点暴露一个异步对象引脚，以支持对这个异步行为的进一步操作。
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在源码里的用处一是UBlueprintAsyncActionBase的子类，二是UGameplayTask子类，皆是分别会有另外的UK2Node_BaseAsyncTask以及UK2Node_LatentGameplayTaskCall来解析类的声明定义并包装生成相应的异步蓝图节点。
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基类都是继承自UBlueprintAsyncActionBase。利用ExposedAsyncProxy 指定异步任务对象的名字。在异步蓝图节点上继续返回异步对象，可以在之后支持取消该异步操作。
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## 测试代码：
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UCancellableAsyncAction是引擎提供的继承自UBlueprintAsyncActionBase的一个便利的子类。UMyFunction_Async 定义了一个蓝图异步节点DelayLoop。
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```cpp
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DECLARE_DYNAMIC_MULTICAST_DELEGATE(FDelayOutputPin);
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UCLASS(Blueprintable, BlueprintType,meta = (ExposedAsyncProxy = MyAsyncObject))
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class INSIDER_API UMyFunction_Async :public UBlueprintAsyncActionBase
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{
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public:
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GENERATED_BODY()
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public:
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UPROPERTY(BlueprintAssignable)
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FDelayOutputPin Loop;
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UPROPERTY(BlueprintAssignable)
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FDelayOutputPin Complete;
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UFUNCTION(BlueprintCallable, meta = (BlueprintInternalUseOnly = "true", WorldContext = "WorldContextObject"), Category = "Flow Control")
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static UMyFunction_Async* DelayLoop(const UObject* WorldContextObject, const float DelayInSeconds, const int Iterations);
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virtual void Activate() override;
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UFUNCTION()
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static void Test();
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private:
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const UObject* WorldContextObject = nullptr;
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float MyDelay = 0.f;
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int MyIterations = 0;
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bool Active = false;
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UFUNCTION()
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void ExecuteLoop();
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UFUNCTION()
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void ExecuteComplete();
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};
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```
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## 默认的蓝图节点是：
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如果UMyFunction_Async 直接继承自UBlueprintAsyncActionBase，并且没有设置ExposedAsyncProxy，则生成的蓝图异步节点为为下图。
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而如果继承自UCancellableAsyncAction (提供了Cancel方法)，并且设置ExposedAsyncProxy 为自己想要的AsyncObject引脚名称。
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```cpp
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UCLASS(Abstract, BlueprintType, meta = (ExposedAsyncProxy = AsyncAction), MinimalAPI)
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class UCancellableAsyncAction : public UBlueprintAsyncActionBase
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{
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UFUNCTION(BlueprintCallable, Category = "Async Action")
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ENGINE_API virtual void Cancel();
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}
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DECLARE_DYNAMIC_MULTICAST_DELEGATE(FDelayOutputPin);
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UCLASS(Blueprintable, BlueprintType,meta = (ExposedAsyncProxy = MyAsyncObject))
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class INSIDER_API UMyFunction_Async :public UCancellableAsyncAction
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{}
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```
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## 修改后的效果如下图：
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## 该Meta在源码中发生的位置：
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```cpp
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void UK2Node_BaseAsyncTask::AllocateDefaultPins()
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{
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bool bExposeProxy = false;
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bool bHideThen = false;
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FText ExposeProxyDisplayName;
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for (const UStruct* TestStruct = ProxyClass; TestStruct; TestStruct = TestStruct->GetSuperStruct())
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{
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bExposeProxy |= TestStruct->HasMetaData(TEXT("ExposedAsyncProxy"));
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bHideThen |= TestStruct->HasMetaData(TEXT("HideThen"));
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if (ExposeProxyDisplayName.IsEmpty())
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{
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ExposeProxyDisplayName = TestStruct->GetMetaDataText(TEXT("ExposedAsyncProxy"));
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}
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}
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if (bExposeProxy)
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{
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UEdGraphPin* ProxyPin = CreatePin(EGPD_Output, UEdGraphSchema_K2::PC_Object, ProxyClass, FBaseAsyncTaskHelper::GetAsyncTaskProxyName());
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if (!ExposeProxyDisplayName.IsEmpty())
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{
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ProxyPin->PinFriendlyName = ExposeProxyDisplayName;
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}
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}
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}
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```
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