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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/UPROPERTY/UHT/FieldNotify/FieldNotify.md

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+# FieldNotify
+
+- **功能描述：** 在打开MVVM插件后，使得该属性变成支持FieldNotify的属性。
+
+- **元数据类型：** bool
+- **引擎模块：** MVVM, UHT
+- **限制类型：** ViewModel里的属性
+- **常用程度：** ★★★★
+
+在打开MVVM插件后，使得该属性变成支持FieldNotify的属性。
+
+## 测试代码：
+
+```cpp
+UCLASS(BlueprintType)
+class INSIDER_API UMyViewModel :public UMVVMViewModelBase
+{
+	GENERATED_BODY()
+protected:
+	UPROPERTY(BlueprintReadWrite, FieldNotify, Getter, Setter, BlueprintSetter = SetHP)
+	float HP = 1.f;
+
+	UPROPERTY(BlueprintReadWrite, FieldNotify, Getter, Setter, BlueprintSetter = SetMaxHP)
+	float MaxHP = 100.f;
+public:
+	float GetHP()const { return HP; }
+	UFUNCTION(BlueprintSetter)
+	void SetHP(float val)
+	{
+		if (UE_MVVM_SET_PROPERTY_VALUE(HP, val))
+		{
+			UE_MVVM_BROADCAST_FIELD_VALUE_CHANGED(GetHPPercent);
+		}
+	}
+
+	float GetMaxHP()const { return MaxHP; }
+	UFUNCTION(BlueprintSetter)
+	void SetMaxHP(float val)
+	{
+		if (UE_MVVM_SET_PROPERTY_VALUE(MaxHP, val))
+		{
+			UE_MVVM_BROADCAST_FIELD_VALUE_CHANGED(GetHPPercent);
+		}
+	}
+
+	//You need to manually notify that GetHealthPercent changed when CurrentHealth or MaxHealth changed.
+	UFUNCTION(BlueprintPure, FieldNotify)
+	float GetHPPercent() const
+	{
+		return (MaxHP != 0.f) ? HP / MaxHP : 0.f;
+	}
+};
+
+```
+
+## 测试效果：
+
+效果一方面是UHT生成的.generated.h里和.gen.cpp里的代码，具体的宏作用就不展开了，大家可查看其他更细致的MVVM相关文章。这里只要知道UHT会为标了FieldNotify的属性定义FFieldId以及FFieldNotificationClassDescriptor来标识一个接受可通知的属性。
+
+```cpp
+//MyViewModel.generated.h
+#define FID_GitWorkspace_Hello_Source_Insider_Property_MVVM_MyViewModel_h_12_FIELDNOTIFY \
+	UE_FIELD_NOTIFICATION_DECLARE_CLASS_DESCRIPTOR_BEGIN(INSIDER_API ) \
+	UE_FIELD_NOTIFICATION_DECLARE_FIELD(HP) \
+	UE_FIELD_NOTIFICATION_DECLARE_FIELD(MaxHP) \
+	UE_FIELD_NOTIFICATION_DECLARE_FIELD(GetHPPercent) \
+	UE_FIELD_NOTIFICATION_DECLARE_ENUM_FIELD_BEGIN(HP) \
+	UE_FIELD_NOTIFICATION_DECLARE_ENUM_FIELD(MaxHP) \
+	UE_FIELD_NOTIFICATION_DECLARE_ENUM_FIELD(GetHPPercent) \
+	UE_FIELD_NOTIFICATION_DECLARE_ENUM_FIELD_END() \
+	UE_FIELD_NOTIFICATION_DECLARE_CLASS_DESCRIPTOR_END();
+//MyViewModel.gen.cpp
+	UE_FIELD_NOTIFICATION_IMPLEMENT_FIELD(UMyViewModel, HP)
+	UE_FIELD_NOTIFICATION_IMPLEMENT_FIELD(UMyViewModel, MaxHP)
+	UE_FIELD_NOTIFICATION_IMPLEMENT_FIELD(UMyViewModel, GetHPPercent)
+	UE_FIELD_NOTIFICATION_IMPLEMENTATION_BEGIN(UMyViewModel)
+	UE_FIELD_NOTIFICATION_IMPLEMENT_ENUM_FIELD(UMyViewModel, HP)
+	UE_FIELD_NOTIFICATION_IMPLEMENT_ENUM_FIELD(UMyViewModel, MaxHP)
+	UE_FIELD_NOTIFICATION_IMPLEMENT_ENUM_FIELD(UMyViewModel, GetHPPercent)
+	UE_FIELD_NOTIFICATION_IMPLEMENTATION_END(UMyViewModel);
+```
+
+蓝图效果：
+
+这些控件的属性就可以和ViewModel里的属性绑定起来。
+
+![Untitled](Untitled.png)