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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/AnimationGraph/PinShownByDefault/PinShownByDefault.md

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+# PinShownByDefault
+
+- **功能描述：** 在动画蓝图中使得动画节点的某个属性一开始就暴露出来成为引脚，但也可以改变。
+- **使用位置：** UPROPERTY
+- **引擎模块：** AnimationGraph
+- **元数据类型：** bool
+- **限制类型：** FAnimNode_Base
+- **关联项：** [AlwaysAsPin](../AlwaysAsPin/AlwaysAsPin.md), [NeverAsPin](../NeverAsPin/NeverAsPin.md)
+- **常用程度：** ★★★
+
+在动画蓝图中使得动画节点的某个属性一开始就暴露出来成为引脚。
+
+和常规的蓝图不同，FAnimNode_Base里面的属性默认是不在节点上显示出来的。因此才需要这个meta显式的指定哪些需要显式。
+
+PinShownByDefault目前只在动画蓝图节点上应用。
+
+相反的，可以用PinHiddenByDefault来隐藏属性成为引脚。
+
+## 测试代码：
+
+```cpp
+USTRUCT(BlueprintInternalUseOnly)
+struct INSIDEREDITOR_API FAnimNode_MyTestPinShown : public FAnimNode_Base
+{
+	GENERATED_USTRUCT_BODY()
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinShownByDefaultTest)
+	int32 MyInt_NotShown = 123;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinShownByDefaultTest, meta = (PinShownByDefault))
+	int32 MyInt_PinShownByDefault = 123;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinShownByDefaultTest, meta = (AlwaysAsPin))
+	int32 MyInt_AlwaysAsPin = 123;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinShownByDefaultTest, meta = (NeverAsPin))
+	int32 MyInt_NeverAsPin = 123;
+};
+
+UCLASS()
+class INSIDEREDITOR_API UAnimGraphNode_MyTestPinShown : public UAnimGraphNode_Base
+{
+	GENERATED_UCLASS_BODY()
+
+	UPROPERTY(EditAnywhere, Category = Settings)
+	FAnimNode_MyTestPinShown Node;
+};
+```
+
+## 测试效果：
+
+可见，同样的两个属性，MyInt_NotShown 默认情况不显示成节点，只能在细节面板里编辑。而MyInt_PinShownByDefault默认情况下成为引脚。当PinShownByDefault还可以改变去掉Pin的功能。
+
+![PinShown](PinShown.gif)
+
+## 原理：
+
+源码里唯一用的地方就是在FAnimBlueprintNodeOptionalPinManager，其实就是处理动画蓝图节点的Pin如何显示。
+
+```cpp
+void FAnimBlueprintNodeOptionalPinManager::GetRecordDefaults(FProperty* TestProperty, FOptionalPinFromProperty& Record) const
+{
+	const UAnimationGraphSchema* Schema = GetDefault<UAnimationGraphSchema>();
+
+	// Determine if this is a pose or array of poses
+	FArrayProperty* ArrayProp = CastField<FArrayProperty>(TestProperty);
+	FStructProperty* StructProp = CastField<FStructProperty>(ArrayProp ? ArrayProp->Inner : TestProperty);
+	const bool bIsPoseInput = (StructProp  && StructProp->Struct->IsChildOf(FPoseLinkBase::StaticStruct()));
+
+	//@TODO: Error if they specified two or more of these flags
+	const bool bAlwaysShow = TestProperty->HasMetaData(Schema->NAME_AlwaysAsPin) || bIsPoseInput;
+	const bool bOptional_ShowByDefault = TestProperty->HasMetaData(Schema->NAME_PinShownByDefault);
+	const bool bOptional_HideByDefault = TestProperty->HasMetaData(Schema->NAME_PinHiddenByDefault);
+	const bool bNeverShow = TestProperty->HasMetaData(Schema->NAME_NeverAsPin);
+	const bool bPropertyIsCustomized = TestProperty->HasMetaData(Schema->NAME_CustomizeProperty);
+	const bool bCanTreatPropertyAsOptional = CanTreatPropertyAsOptional(TestProperty);
+
+	Record.bCanToggleVisibility = bCanTreatPropertyAsOptional && (bOptional_ShowByDefault || bOptional_HideByDefault);
+	Record.bShowPin = bAlwaysShow || bOptional_ShowByDefault;
+	Record.bPropertyIsCustomized = bPropertyIsCustomized;
+}
+```