114 lines
3.4 KiB
Markdown
114 lines
3.4 KiB
Markdown
# ScriptConstant
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- **功能描述：** 把一个静态函数的返回值包装成为一个常量值。
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- **使用位置：** UFUNCTION
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- **引擎模块：** Script
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- **元数据类型：** string="abc"
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- **关联项：** [ScriptConstantHost](ScriptConstantHost.md)
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- **常用程度：** ★★★
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把一个静态函数的返回值包装成为一个常量值。
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- 函数的名字即为常量的默认名称，但ScriptConstant也可以额外提供一个自定义名称。
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- 常量作用域默认存在于该静态函数的外部类中，但也可以通过ScriptConstantHost来指定到另外一个类型中。
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## 测试代码：
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```cpp
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USTRUCT(BlueprintType)
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struct INSIDER_API FMyPythonConstantStruct
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{
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GENERATED_BODY()
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public:
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UPROPERTY(BlueprintReadWrite, EditAnywhere)
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FString MyString;
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};
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyPython_ConstantOwner :public UObject
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{
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GENERATED_BODY()
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public:
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};
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyPython_Constant_Test :public UObject
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{
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GENERATED_BODY()
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public:
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UFUNCTION(BlueprintPure, meta = (ScriptConstant))
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static int32 MyIntConst() { return 123; }
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UFUNCTION(BlueprintPure, meta = (ScriptConstant = "MyOtherIntConst"))
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static int32 MyIntConst2() { return 456; }
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UFUNCTION(BlueprintPure, meta = (ScriptConstant))
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static FMyPythonConstantStruct MyStructConst() { return FMyPythonConstantStruct{ TEXT("Hello") }; }
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UFUNCTION(BlueprintPure, meta = (ScriptConstant = "MyOtherStructConst"))
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static FMyPythonConstantStruct MyStructConst2() { return FMyPythonConstantStruct{ TEXT("World") }; }
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public:
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UFUNCTION(BlueprintPure, meta = (ScriptConstant="FirstString", ScriptConstantHost = "/Script/Insider.MyPython_ConstantOwner"))
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static FString MyStringConst() { return TEXT("First"); }
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****};
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```
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## 生成的Py代码：
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```cpp
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class MyPython_Constant_Test(Object):
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r"""
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My Python Constant Test
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**C++ Source:**
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- **Module**: Insider
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- **File**: MyPython_ScriptConstant.h
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"""
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MY_OTHER_STRUCT_CONST: MyPythonConstantStruct #: (MyPythonConstantStruct): My Struct Const 2
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MY_STRUCT_CONST: MyPythonConstantStruct #: (MyPythonConstantStruct): My Struct Const
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MY_OTHER_INT_CONST: int #: (int32): My Int Const 2
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MY_INT_CONST: int #: (int32): My Int Const
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class MyPython_ConstantOwner(Object):
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r"""
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**My Python Constant Owner
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**C++ Source:**
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- **Module**: Insider
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- **File**: MyPython_ScriptConstant.h
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"""
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FIRST_STRING: str #: (str): My String Const
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```
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## 运行的结果：
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可见在类中生成了相应的常量。而MyStringConst因为指定了ScriptConstantHost 而生成在别的类中。
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```cpp
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LogPython: print(unreal.MyPython_Constant_Test.MY_INT_CONST)
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LogPython: 123
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LogPython: print(unreal.MyPython_Constant_Test.MY_OTHER_INT_CONST)
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LogPython: 456
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LogPython: print(unreal.MyPython_Constant_Test.MY_OTHER_STRUCT_CONST)
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LogPython: <Struct 'MyPythonConstantStruct' (0x00000A0FC4051F00) {my_string: "World"}>
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LogPython: print(unreal.MyPython_Constant_Test.MY_STRUCT_CONST)
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LogPython: <Struct 'MyPythonConstantStruct' (0x00000A0FC4051EA0) {my_string: "Hello"}>
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LogPython: print(unreal.MyPython_ConstantOwner.FIRST_STRING)
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LogPython: First
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```
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## 原理：
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生成的逻辑在这个GenerateWrappedConstant 函数里。
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```cpp
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auto GenerateWrappedConstant = [this, &GeneratedWrappedType, &OutGeneratedWrappedTypeReferences, &OutDirtyModules](const UFunction* InFunc)
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{}
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```
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