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

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/UHT/FieldNotifyInterfaceParam/FieldNotifyInterfaceParam.md

@@ -0,0 +1,53 @@
+# FieldNotifyInterfaceParam
+
+- **功能描述：** 指定函数的某个参数提供FieldNotify的ViewModel信息。
+- **使用位置：** UFUNCTION
+- **引擎模块：** FieldNotify
+- **元数据类型：** string="abc"
+- **限制类型：** 函数里有其他FFieldNotificationId 参数
+- **常用程度：** ★★★
+
+指定函数的某个参数提供FieldNotify的ViewModel信息。
+
+该参数为之后的FFieldNotificationId参数的提供上下文信息，这样FieldId的选项框才知道有哪些可选值。
+
+## 源码例子：
+
+```cpp
+	/** Broadcast that the Field value changed. */
+	UFUNCTION(BlueprintCallable, Category = "FieldNotification", meta = (FieldNotifyInterfaceParam="Object", DisplayName = "Broadcast Field Value Changed"))
+	static void BroadcastFieldValueChanged(UObject* Object, FFieldNotificationId FieldId);
+
+```
+
+## 蓝图效果：
+
+在UserWidget里测试，可见没有连接到参数的Target默认为当前的UserWidget，则FieldId是3个值。而连接到我们自定义的ViewModel后，则改变为我们下面定义的值。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+```cpp
+TSharedRef<SWidget> SFieldNotificationGraphPin::GetDefaultValueWidget()
+{
+	UEdGraphPin* SelfPin = GraphPinObj->GetOwningNode()->FindPin(UEdGraphSchema_K2::PSC_Self);
+	if (UK2Node_CallFunction* CallFunction = Cast<UK2Node_CallFunction>(GraphPinObj->GetOwningNode()))
+	{
+		if (UFunction* Function = CallFunction->GetTargetFunction())
+		{
+			const FString& PinName = Function->GetMetaData("FieldNotifyInterfaceParam");
+			if (PinName.Len() != 0)
+			{
+				SelfPin = GraphPinObj->GetOwningNode()->FindPin(*PinName);
+			}
+		}
+	}
+
+	return SNew(SFieldNotificationPicker)
+		.Value(this, &SFieldNotificationGraphPin::GetValue)
+		.OnValueChanged(this, &SFieldNotificationGraphPin::SetValue)
+		.FromClass_Static(Private::GetPinClass, SelfPin)
+		.Visibility(this, &SGraphPin::GetDefaultValueVisibility);
+}
+```