84 lines
3.6 KiB
Markdown
84 lines
3.6 KiB
Markdown
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# Latent
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- **功能描述：** 标明一个函数是一个延迟异步操作
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- **使用位置：** UFUNCTION
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- **引擎模块：** Blueprint
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- **元数据类型：** bool
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- **关联项：** [LatentInfo](LatentInfo.md), [NeedsLatentFixup](NeedsLatentFixup.md), [LatentCallbackTarget](LatentCallbackTarget.md)
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- **常用程度：** ★★★★★
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标明一个函数是一个延迟异步操作，需要配合LatentInfo来使用。
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会导致在逻辑执行上Then（也叫Complete）引脚需要手动触发（引擎内部触发），且函数右上角增加时钟的图标。
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## 测试代码：
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```cpp
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class FMySleepAction : public FPendingLatentAction
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{
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public:
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float TimeRemaining;
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FName ExecutionFunction;
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int32 OutputLink;
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FWeakObjectPtr CallbackTarget;
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FMySleepAction(float Duration, const FLatentActionInfo& LatentInfo)
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: TimeRemaining(Duration)
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, ExecutionFunction(LatentInfo.ExecutionFunction)
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, OutputLink(LatentInfo.Linkage)
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, CallbackTarget(LatentInfo.CallbackTarget)
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{
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}
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virtual void UpdateOperation(FLatentResponse& Response) override
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{
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TimeRemaining -= Response.ElapsedTime();
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Response.FinishAndTriggerIf(TimeRemaining <= 0.0f, ExecutionFunction, OutputLink, CallbackTarget);
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}
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};
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyFunction_Latent :public UBlueprintFunctionLibrary
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{
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public:
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GENERATED_BODY()
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public:
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UFUNCTION(BlueprintCallable, meta = (Latent, WorldContext = "WorldContextObject", LatentInfo = "LatentInfo", Duration = "5"))
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static void MySleep(const UObject* WorldContextObject, float Duration, FLatentActionInfo LatentInfo)
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{
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if (UWorld* World = GEngine->GetWorldFromContextObject(WorldContextObject, EGetWorldErrorMode::LogAndReturnNull))
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{
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FLatentActionManager& LatentActionManager = World->GetLatentActionManager();
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if (LatentActionManager.FindExistingAction<FMySleepAction>(LatentInfo.CallbackTarget, LatentInfo.UUID) == NULL)
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{
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LatentActionManager.AddNewAction(LatentInfo.CallbackTarget, LatentInfo.UUID, new FMySleepAction(Duration, LatentInfo));
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}
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}
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}
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UFUNCTION(BlueprintCallable, meta = (Latent, WorldContext = "WorldContextObject", Duration = "5"))
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static void MySleep2(const UObject* WorldContextObject, float Duration, FLatentActionInfo LatentInfo);
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};
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```
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## 蓝图效果：
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MySleep可以像Delay一样正常工作。但是MySleep2因为没有标明LatentInfo，因此LatentInfo函数参数没有被蓝图系统赋值，导致无法工作。
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在源码里Latent使用的非常频繁，最常见的例子：
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```cpp
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UFUNCTION(BlueprintCallable, meta=(WorldContext="WorldContextObject", Latent = "", LatentInfo = "LatentInfo", DisplayName = "Load Stream Level (by Name)"), Category="Game")
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static ENGINE_API void LoadStreamLevel(const UObject* WorldContextObject, FName LevelName, bool bMakeVisibleAfterLoad, bool bShouldBlockOnLoad, FLatentActionInfo LatentInfo);
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UFUNCTION(BlueprintCallable, meta = (Latent, LatentInfo = "LatentInfo", WorldContext = "WorldContextObject", BlueprintInternalUseOnly = "true"), Category = "Utilities")
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static ENGINE_API void LoadAsset(const UObject* WorldContextObject, TSoftObjectPtr<UObject> Asset, FOnAssetLoaded OnLoaded, FLatentActionInfo LatentInfo);
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UFUNCTION(BlueprintCallable, Category="Utilities|FlowControl", meta=(Latent, WorldContext="WorldContextObject", LatentInfo="LatentInfo", Duration="0.2", Keywords="sleep"))
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static ENGINE_API void Delay(const UObject* WorldContextObject, float Duration, struct FLatentActionInfo LatentInfo );
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```
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关于使用Latent还是继承自UBlueprintAsyncActionBase来创建蓝图异步节点的差异，可以在网上别的文章查看。
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