vault backup: 2024-10-12 17:19:45

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/DetailsPanel/MaxPropertyDepth/MaxPropertyDepth.md

@@ -0,0 +1,130 @@
+# MaxPropertyDepth
+
+- **功能描述：** 指定对象或结构在细节面板里展开的层数。
+- **使用位置：** UPROPERTY
+- **引擎模块：** DetailsPanel
+- **元数据类型：** int32
+- **限制类型：** 对象或结构属性
+- **常用程度：** ★
+
+指定对象或结构在细节面板里展开的层数。
+
+- 默认是没有限制的，可以一直递归展开到最深层次字段。
+- 如果对象的子对象再有子对象，这样递归很多层级，可能我们会想要限制不想展开太深，因此我们可以指定一个层级限制。
+- 取值-1表示没有限制，0表示完全不展开，>0表示限制的层数。
+- 源码里没有找到例子，但却是可以工作的。
+
+## 测试代码：
+
+```cpp
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStructDepth1
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	int32 MyInt1 = 123;
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FString MyString1;
+};
+
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStructDepth2
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FMyStructDepth1 MyStruct1;
+};
+
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStructDepth3
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FMyStructDepth2 MyStruct2;
+};
+
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStructDepth4
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FMyStructDepth3 MyStruct3;
+};
+
+UCLASS(BlueprintType)
+class INSIDER_API UMyProperty_MaxPropertyDepth :public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite)
+	FMyStructDepth4 MyStruct;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite,meta=(MaxPropertyDepth=2))
+	FMyStructDepth4 MyStruct_Depth;
+};
+
+```
+
+## 测试效果：
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+在每个FPropertyNode构建子节点的时候，检查一下当前的MaxChildDepthAllowed ，超过了就不继续往下构建。
+
+```cpp
+/** Safety Value representing Depth in the property tree used to stop diabolical topology cases
+ * -1 = No limit on children
+ *  0 = No more children are allowed.  Do not process child nodes
+ *  >0 = A limit has been set by the property and will tick down for successive children
+ */
+int32 MaxChildDepthAllowed;
+
+void FPropertyNode::InitNode(const FPropertyNodeInitParams& InitParams)
+{
+	
+		//Get the property max child depth
+		static const FName Name_MaxPropertyDepth("MaxPropertyDepth");
+		if (Property->HasMetaData(Name_MaxPropertyDepth))
+		{
+			int32 NewMaxChildDepthAllowed = Property->GetIntMetaData(Name_MaxPropertyDepth);
+			//Ensure new depth is valid.  Otherwise just let the parent specified value stand
+			if (NewMaxChildDepthAllowed > 0)
+			{
+				//if there is already a limit on the depth allowed, take the minimum of the allowable depths
+				if (MaxChildDepthAllowed >= 0)
+				{
+					MaxChildDepthAllowed = FMath::Min(MaxChildDepthAllowed, NewMaxChildDepthAllowed);
+				}
+				else
+				{
+					//no current limit, go ahead and take the new limit
+					MaxChildDepthAllowed = NewMaxChildDepthAllowed;
+				}
+			}
+		}
+}
+
+void FPropertyNode::RebuildChildren()
+{
+	if (MaxChildDepthAllowed != 0)
+{
+	//the case where we don't want init child nodes is when an Item has children that we don't want to display
+	//the other option would be to make each node "Read only" under that item.
+	//The example is a material assigned to a static mesh.
+	if (HasNodeFlags(EPropertyNodeFlags::CanBeExpanded) && (ChildNodes.Num() == 0))
+	{
+		InitChildNodes();
+		if (ExpandedPropertyItemSet.Size() > 0)
+		{
+			FPropertyNodeUtils::SetExpandedItems(ThisAsSharedRef, ExpandedPropertyItemSet);
+		}
+	}
+}
+}
+```