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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Development/DevelopmentOnly/DevelopmentOnly.md

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+# DevelopmentOnly
+
+- **功能描述：** 使得一个函数变为DevelopmentOnly，意味着只会在Development模式中运行。适用于调试输出之类的功能，但在最终发布版中会跳过。
+- **使用位置：** UFUNCTION
+- **引擎模块：** Development
+- **元数据类型：** bool
+- **常用程度：** ★
+
+使得一个函数变为DevelopmentOnly，意味着只会在Development模式中运行。适用于调试输出之类的功能，但在最终发布版中会跳过。
+
+源码中最典型的例子就是PrintString。
+
+## 测试代码：
+
+```cpp
+	UFUNCTION(BlueprintCallable,meta=(DevelopmentOnly))
+	static void MyFunc_DevelopmentOnly(){}
+
+	UFUNCTION(BlueprintCallable,meta=())
+	static void MyFunc_NotDevelopmentOnly(){}
+```
+
+## 蓝图效果：
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+其会改变这个函数蓝图节点的状态为DevelopmentOnly，从而最终导致该node在shipping模式下被pass through。
+
+```cpp
+void UK2Node_CallFunction::Serialize(FArchive& Ar)
+{
+		if (const UFunction* Function = GetTargetFunction())
+		{
+					// Enable as development-only if specified in metadata. This way existing functions that have the metadata added to them will get their enabled state fixed up on load.
+					if (GetDesiredEnabledState() == ENodeEnabledState::Enabled && Function->HasMetaData(FBlueprintMetadata::MD_DevelopmentOnly))
+					{
+						SetEnabledState(ENodeEnabledState::DevelopmentOnly, /*bUserAction=*/ false);
+					}
+					// Ensure that if the metadata is removed, we also fix up the enabled state to avoid leaving it set as development-only in that case.
+					else if (GetDesiredEnabledState() == ENodeEnabledState::DevelopmentOnly && !Function->HasMetaData(FBlueprintMetadata::MD_DevelopmentOnly))
+					{
+						SetEnabledState(ENodeEnabledState::Enabled, /*bUserAction=*/ false);
+					}
+		}
+}
+```