99 lines
3.8 KiB
Markdown
99 lines
3.8 KiB
Markdown
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# ExposeOnSpawn
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- **功能描述：** 使该属性在ContructObject或SpawnActor等创建对象的时候暴露出来。
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- **使用位置：** UPROPERTY
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- **引擎模块：** Blueprint
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- **元数据类型：** bool
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- **常用程度：** ★★★★★
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使该属性在ContructObject或SpawnActor等创建对象的时候暴露出来。
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- 具体来说，通过在源码搜索，这个标记在UK2Node_AddComponent，UK2Node_ConstructObjectFromClass，UK2Node_SpawnActor，UK2Node_LatentGameplayTaskCall的时候用到。
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- 在C++里设置的效果等同于在蓝图里勾上ExposeOnSpawn。
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- 该meta的设置也会同时设置到PropertyFlags里的CPF_ExposeOnSpawn
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## 测试代码：
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```cpp
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UCLASS(BlueprintType)
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class INSIDER_API UMyProperty_ExposeOnSpawn :public UObject
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{
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GENERATED_BODY()
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public:
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// (Category = MyProperty_ExposeOnSpawn, ModuleRelativePath = Property/Blueprint/MyProperty_ExposeOnSpawn.h)
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// PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(EditAnywhere, BlueprintReadWrite)
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FString MyString = TEXT("First");
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// (Category = MyProperty_ExposeOnSpawn, ExposeOnSpawn = , ModuleRelativePath = Property/Blueprint/MyProperty_ExposeOnSpawn.h)
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// PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_ExposeOnSpawn | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (ExposeOnSpawn))
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FString MyString_ExposeOnSpawn = TEXT("Second");
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};
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```
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## 测试效果：
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可见MyString_ExposeOnSpawn 暴露了出来，而MyString 没有。
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## 原理：
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在UHT的时候会分析如果包含ExposeOnSpawn就会同步设置CPF_ExposeOnSpawn。
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而在IsPropertyExposedOnSpawn这个函数里具体判断是否要暴露，这个函数被上述的4个函数节点引用。源码里举UK2Node_ConstructObjectFromClass里的CreatePinsForClass作为例子，可见只有bIsExposedToSpawn 的时候才会为蓝图节点开始创建额外的Pin引脚。
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```cpp
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if (propertySettings.MetaData.ContainsKey(UhtNames.ExposeOnSpawn))
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{
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propertySettings.PropertyFlags |= EPropertyFlags.ExposeOnSpawn;
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}
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bool UEdGraphSchema_K2::IsPropertyExposedOnSpawn(const FProperty* Property)
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{
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Property = FBlueprintEditorUtils::GetMostUpToDateProperty(Property);
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if (Property)
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{
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const bool bMeta = Property->HasMetaData(FBlueprintMetadata::MD_ExposeOnSpawn);
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const bool bFlag = Property->HasAllPropertyFlags(CPF_ExposeOnSpawn);
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if (bMeta != bFlag)
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{
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const FCoreTexts& CoreTexts = FCoreTexts::Get();
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UE_LOG(LogBlueprint, Warning
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, TEXT("ExposeOnSpawn ambiguity. Property '%s', MetaData '%s', Flag '%s'")
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, *Property->GetFullName()
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, bMeta ? *CoreTexts.True.ToString() : *CoreTexts.False.ToString()
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, bFlag ? *CoreTexts.True.ToString() : *CoreTexts.False.ToString());
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}
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return bMeta || bFlag;
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}
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return false;
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}
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void UK2Node_ConstructObjectFromClass::CreatePinsForClass(UClass* InClass, TArray<UEdGraphPin*>* OutClassPins)
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{
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for (TFieldIterator<FProperty> PropertyIt(InClass, EFieldIteratorFlags::IncludeSuper); PropertyIt; ++PropertyIt)
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{
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FProperty* Property = *PropertyIt;
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UClass* PropertyClass = CastChecked<UClass>(Property->GetOwner<UObject>());
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const bool bIsDelegate = Property->IsA(FMulticastDelegateProperty::StaticClass());
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const bool bIsExposedToSpawn = UEdGraphSchema_K2::IsPropertyExposedOnSpawn(Property);
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const bool bIsSettableExternally = !Property->HasAnyPropertyFlags(CPF_DisableEditOnInstance);
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if( bIsExposedToSpawn &&
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!Property->HasAnyPropertyFlags(CPF_Parm) &&
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bIsSettableExternally &&
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Property->HasAllPropertyFlags(CPF_BlueprintVisible) &&
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!bIsDelegate &&
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(nullptr == FindPin(Property->GetFName()) ) &&
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FBlueprintEditorUtils::PropertyStillExists(Property))
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{
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if (UEdGraphPin* Pin = CreatePin(EGPD_Input, NAME_None, Property->GetFName()))
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{
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}
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```
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