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

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Container/EditFixedOrder/EditFixedOrder.md

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+# EditFixedOrder
+
+- **功能描述：** 使数组的元素无法通过拖拽来重新排序。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Container Property
+- **元数据类型：** bool
+- **限制类型：** TArray
+- **常用程度：** ★★
+
+## 测试代码：
+
+```cpp
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest)
+	TArray<int32> MyIntArray_NoEditFixedOrder;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest, meta = (EditFixedOrder))
+	TArray<int32> MyIntArray_EditFixedOrder;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest)
+	TSet<int32> MyIntSet_NoEditFixedOrder;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest, meta = (EditFixedOrder))
+	TSet<int32> MyIntSet_EditFixedOrder;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest)
+	TMap<int32,FString> MyIntMap_NoEditFixedOrder;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = EditFixedOrderTest, meta = (EditFixedOrder))
+	TMap<int32,FString> MyIntMap_EditFixedOrder;
+```
+
+## 测试效果：
+
+- 可见只有第一个MyIntArray_NoEditFixedOrder，在数组元素上出现可拖拽的标记，然后可以改变顺序。
+- 加上EditFixedOrder的TArray就无法改变顺序了。
+- 其他TSet，TMap是不支持该meta的，因为其内部本身顺序也无关。
+
+![EditFixedOrder](EditFixedOrder.gif)
+
+## 原理：
+
+可以看见，细节面板里一个属性行是否可重排序的判断是外部是个数组，且没有EditFixedOrder和ArraySizeEnum（固定数组）。当然本身这个属性也要在可编辑状态（比如被禁用灰掉就显然不可编辑了）
+
+```cpp
+bool FPropertyNode::IsReorderable()
+{
+	FProperty* NodeProperty = GetProperty();
+	if (NodeProperty == nullptr)
+	{
+		return false;
+	}
+	// It is reorderable if the parent is an array and metadata doesn't prohibit it
+	const FArrayProperty* OuterArrayProp = NodeProperty->GetOwner<FArrayProperty>();
+
+	static const FName Name_DisableReordering("EditFixedOrder");
+	static const FName NAME_ArraySizeEnum("ArraySizeEnum");
+	return OuterArrayProp != nullptr 
+		&& !OuterArrayProp->HasMetaData(Name_DisableReordering)
+		&& !IsEditConst()
+		&& !OuterArrayProp->HasMetaData(NAME_ArraySizeEnum)
+		&& !FApp::IsGame();
+}
+```