【UE4 C++ 基础知识】<1> UPROPERTY宏、属性说明符、元数据说明符

属性声明

• 属性使用标准的C++变量语法声明，前面用UPROPERTY宏来定义属性元数据和变量说明符。

UPROPERTY([specifier, specifier, ...], [meta(key=value, key=value, ...)])
Type VariableName;

• 示例：位掩码

UENUM(BlueprintType)
enum class EColorBits1 :uint8
{
	ECB_Red,
	ECB_Green,
	ECB_Blue,
};

//使用"bitflags"元标记来创建UENUM，实际使用似乎没差别
UENUM(BlueprintType, Meta = (Bitflags))
enum class EColorBits2 :uint8
{
	ECB_Red,
	ECB_Green,
	ECB_Blue,
};

UPROPERTY(EditAnywhere, Meta = (Bitmask))
	int32 BasicBits;

UPROPERTY(BlueprintReadWrite, EditAnywhere)
	EColorBits1 ColorBits1;

UPROPERTY(BlueprintReadWrite, EditAnywhere)
	EColorBits2 ColorBits2;

UPROPERTY(BlueprintReadWrite, EditAnywhere, Meta = (Bitmask, BitmaskEnum = "EColorBits1"))
	int32 ColorFlags3;

UPROPERTY(BlueprintReadWrite, EditAnywhere, Meta = (Bitmask, BitmaskEnum = "EColorBits2"))
	int32 ColorFlags4;

在上述示例中， ECB_Red 值为0，表示它被选中时将激活位0（将ColorFlags增加1）。ECB_Green对应于位1（将ColorFlags增加2），ECB_Blue 对应于位2（将ColorFlags增加4）。

属性说明符

作用

• 声明属性时，属性说明符 可被添加到声明，以控制属性与引擎和编辑器诸多方面的相处方式。

常用说明符

VisibleDefaultsOnly

// 仅在 Class Defaults 可见
UPROPERTY(VisibleDefaultsOnly)
	int32 VisibleDefaultsOnlyInt;

VisibleInstanceOnly

// 仅在实例化 Detail 可见
UPROPERTY(VisibleInstanceOnly)
	FVector VisibleInstanceOnlyVector;

VisibleAnywhere

//Class Defaults 和 实例化 Detail 可见
UPROPERTY(VisibleAnywhere)
	FString VisibleAnywhereString;

EditDefaultsOnly

//仅在 Class Defaults 可编辑
UPROPERTY(EditDefaultsOnly)
	int32 EditDefaultsOnlyInt;

EditInstanceOnly

//仅在实例化 Detail 可编辑
UPROPERTY(EditInstanceOnly)
	FVector EditInstanceOnlyVector;

EditAnywhere

//Class Defaults 和 实例化 Detail 可编辑
UPROPERTY(EditAnywhere)
	FString EditAnywhereString;

BlueprintReadOnly

//Variables 只读
UPROPERTY(BlueprintReadOnly)
	int32 intValue_BlueprintReadOnly;

BlueprintReadWrite

//Variables 可读写
UPROPERTY(BlueprintReadWrite)
	int32 intValue_BlueprintReadWrite;

Category 类别

UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="TopCategory")
	int32 intValue1;

UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "TopCategory|SubCategory")
	int32 intValue2;

BlueprintAssignable

DECLARE_DYNAMIC_MULTICAST_DELEGATE_ThreeParams(FNotifyPawnChange, float, PawnHpPercent, float, PawnPhysicalShieldPercent, float, PawnMageShieldPercent);

//蓝图中可绑定委托
UPROPERTY(BlueprintAssignable)
	FNotifyPawnChange NotifyPawnChange;

元数据说明符 meta

作用

声明类、接口、结构体、列举、列举值、函数，或属性时，可添加 元数据说明符 来控制其与引擎和编辑器各方面的相处方式。每一种类型的数据结构或成员都有自己的元数据说明符列表

常见说明符

DisplayName 别名

• 可以便于蓝图变量搜索，如果变量名不好记的话

EditCondition 条件可编辑

• 支持bool、比较等条件判断

UPROPERTY(EditAnywhere,BlueprintReadWrite, meta = (DisplayName="UseOffset1、2 标志位") )
	bool bUseOffset;

UPROPERTY(EditAnywhere, meta = (DisplayName = "ContitionValue 控制 offset3"))
	int32 ContitionValue;

UPROPERTY(EditAnywhere, meta = (DisplayName = "ContitionColorBits 控制 offset4"))
	EColorBits1 ContitionColorBits;

UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (EditCondition = "bUseOffset"))
	float Offset1;

UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (EditCondition = "!bUseOffset"))
	float Offset2;

UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (EditCondition = "ContitionValue>0"))
	float Offset3;

UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (EditCondition = "ContitionColorBits==EColorBits1::ECB_Green"))
	float Offset4;

BindWidget 和 UMG 同名同类型控件绑定

UPROPERTY(EditAnywhere, meta = (BindWidget))
  UImage* TCanvas;

UPROPERTY(EditAnywhere, BlueprintReadWrite , meta = (BindWidget))
  UButton* Btn_Mass;

UMETA 扩展宏

• cpp meta里的中文在蓝图经常会乱码
  • 解决方法一：高级保存选择 Unicode 65001
  • 解决办法二：使用UMETA中的DisplayName
• 可用于Enum的元素别名
• 可用于结构体的元素别名
• 可用于Datatable的别名

UPROPERTY(EditAnywhere)
	FName ChineseName UMETA(DisplayName="中文名");

UPROPERTY(EditAnywhere)
	float Weight UMETA(DisplayName = "体重") = 65.0f;

UPROPERTY(EditAnywhere)
	EColorBits1 FavoriteColorBits UMETA(DisplayName = "最喜欢的颜色")=EColorBits1::ECB_Blue;

参考

UPROPERTY