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+# 黑板
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+
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+用于存储行为树运行时数据，方便行为树获取和设置数据
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+
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+
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+
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+## UBlackboardData
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+
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+作为 Blackboard 的资产，存储所有配置的数据的 Key，每个 Key 都是通过 `FBlackboardEntry` 来表示
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+
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+```cpp
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+UCLASS(BlueprintType, AutoExpandCategories=(Blackboard), MinimalAPI)
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+class UBlackboardData : public UDataAsset
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+{
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+ GENERATED_UCLASS_BODY()
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+ DECLARE_MULTICAST_DELEGATE_OneParam(FKeyUpdate, UBlackboardData* /*asset*/);
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+
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+ UPROPERTY(EditAnywhere, Category=Parent)
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+ TObjectPtr<UBlackboardData> Parent;
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+
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+ UPROPERTY(EditAnywhere, Category=Blackboard)
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+ TArray<FBlackboardEntry> Keys;
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+
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+private:
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+ UPROPERTY()
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+ uint32 bHasSynchronizedKeys : 1;
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+
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+ // 其他工具函数
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+}
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+```
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+
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+`FBlackboardEntry` 存储着 `EntryName` 表示显示名称，`KeyType` 存储着数据类型
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+
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+> KeyType 的类型是 UBlackboardKeyType
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+
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+```cpp
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+USTRUCT()
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+struct FBlackboardEntry
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+{
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+ GENERATED_USTRUCT_BODY()
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+
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+ UPROPERTY(EditAnywhere, Category=Blackboard)
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+ FName EntryName;
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+
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+#if WITH_EDITORONLY_DATA
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+ UPROPERTY(EditAnywhere, Category=Blackboard, Meta=(ToolTip="Optional description to explain what this blackboard entry does."))
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+ FString EntryDescription;
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+
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+ UPROPERTY(EditAnywhere, Category=Blackboard)
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+ FName EntryCategory;
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+#endif // WITH_EDITORONLY_DATA
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+
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+ /** key type and additional properties */
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+ UPROPERTY(EditAnywhere, Instanced, Category=Blackboard)
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+ TObjectPtr<UBlackboardKeyType> KeyType;
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+
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+ /** if set to true then this field will be synchronized across all instances of this blackboard */
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+ UPROPERTY(EditAnywhere, Category=Blackboard)
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+ uint32 bInstanceSynced : 1;
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+
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+ FBlackboardEntry()
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+ : KeyType(nullptr), bInstanceSynced(0)
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+ {}
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+
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+ AIMODULE_API bool operator==(const FBlackboardEntry& Other) const;
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+};
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+```
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+
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+### UBlackboardKeyType
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+
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+`UBlackboardKeyType` 用于表示黑板属性的数值类型
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+
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+```cpp
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+class UBlackboardKeyType : public UObject
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+{
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+protected:
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+ uint16 ValueSize; // 该 KeyType 对应的数据占用内存大小
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+ TEnumAsByte<EBlackboardKeyOperation::Type> SupportedOp; // 该 KeyType 支持的操作类型
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+ uint8 bIsInstanced : 1;
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+ uint8 bCreateKeyInstance : 1;
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+public:
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+ // 其他工具函数
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+}
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+```
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+
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+
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+
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+虽然这里显示的是 Bool、Int、String 等常见的数据类型，但是实际上并没有那么简单
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+
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+| 类型 | 实际类型 | SupportedOp | ValueSize |
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+| --- | --- | --- | --- |
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+| Bool | UBlackboardKeyType_Bool | Basic | sizeof(uint8) |
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+| Class | UBlackboardKeyType_Class | Basic | sizeof(TWeakObjectPtr<UClass>) |
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+| Object | UBlackboardKeyType_Object | Basic | sizeof(FWeakObjectPtr) |
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+| Rotator | UBlackboardKeyType_Rotator | Basic | sizeof(FRotator) |
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+| Vector | UBlackboardKeyType_Vector | Basic | sizeof(FVector) |
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+| Enum | UBlackboardKeyType_Enum | Arithmetic | sizeof(FDataType) |
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+| Float | UBlackboardKeyType_Float | Arithmetic | sizeof(float) |
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+| Int | UBlackboardKeyType_Int | Arithmetic | sizeof(int32) |
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+| Name | UBlackboardKeyType_Name | Text | sizeof(FName) |
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+| String | UBlackboardKeyType_String | Text | 0 |
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+
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+因为 `FString` 的大小不固定，所以不知道 `UBlackboardKeyType_String` 的 `ValueSize`
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+
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+为了存储 `FString`，`UBlackboardKeyType_String` 直接定义了成员属性 `FString StringValue`，并且设置 `bCreateKeyInstance = true`
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+
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+```cpp
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+UBlackboardKeyType_String::UBlackboardKeyType_String(const FObjectInitializer& ObjectInitializer) : Super(ObjectInitializer)
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+{
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+ ValueSize = 0;
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+ bCreateKeyInstance = true;
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+
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+ SupportedOp = EBlackboardKeyOperation::Text;
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+}
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+```
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+`bCreateKeyInstance` 的作用，参考 `UBTNode` 的 `bCreateKeyInstance`，表示是否需要实例化新的 `UBlackboardType` 对象
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+
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+`UBlackboardKeyType_String` 每次都会实例化一个新的对象出来
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+
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+每个类都有自己的 `GetValue` 和 `SetValue` 静态函数
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+
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+```cpp
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+static AIMODULE_API float GetValue(const UBlackboardKeyType_Float* KeyOb, const uint8* RawData);
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+static AIMODULE_API bool SetValue(UBlackboardKeyType_Float* KeyOb, uint8* RawData, float Value);
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+```
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+
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+> UBlackboardKeyType_Float 的示例
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+
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+与 `UBTNode` 类型，获取 或者 设置 一个 `UBlackboardKeyType` 会传入 对应的对象 和 地址
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+
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+在 `UBlackboardComponent` 中存在一个连续的内存空间，用于存储 Balckboard 中对应项的具体数据内容
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+
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+因为每个 `UBlackboardKeyType` 的 ValueSize 都是确定的，那么每个 `UBlackboardKeyType` 在连续内存中的地址偏移也是固定的，可以通过地址偏移计算得到数据的原始地址，也就是 RowData
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+
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+```cpp
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+float UBlackboardKeyType_Float::GetValue(const UBlackboardKeyType_Float* KeyOb, const uint8* RawData)
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+{
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+ return GetValueFromMemory<float>(RawData);
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+}
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+
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+template<typename T>
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+static T GetValueFromMemory(const uint8* MemoryBlock)
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+{
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+ return *((T*)MemoryBlock);
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+}
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+```
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+
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+> 以 `UBlackboardKeyType_Float` 为例
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+
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+如果 `bCreateKeyInstance` 为 true，那么会为每个 `UBlackboardKeyType` 都创建一个新的对象出来，无需计算地址偏移
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+
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+```cpp
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+FString UBlackboardKeyType_String::GetValue(const UBlackboardKeyType_String* KeyOb, const uint8* RawData)
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+{
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+ return KeyOb->StringValue;
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+}
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+```
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+
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+> 以 `UBlackboardKeyType_String` 为例
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+
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+通常将 `UBlackboardKeyType` 的 `SupportOp` 分为三三种
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+
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+- `Basic` 表示支持最基本的操作：相等性判断（Equal/Not Equal）和赋值操作（Set Value）
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+- `Arithmetic` 表示支持数学运算：加/减/乘/除等算术操作，以及大小比较（Greater/Less等）
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+- `Text` 表示支持字符串操作：包含/匹配/连接等文本处理
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+
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+为了支持 `CompareValues` 操作，相等性判断是通过重写 `CompareValues` 来实现的
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+
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+```cpp
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+EBlackboardCompare::Type UBlackboardKeyType_String::CompareValues(const UBlackboardComponent& OwnerComp, const uint8* MemoryBlock,
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+ const UBlackboardKeyType* OtherKeyOb, const uint8* OtherMemoryBlock) const
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+{
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+ const FString MyValue = GetValue(this, MemoryBlock);
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+ const FString OtherValue = GetValue((UBlackboardKeyType_String*)OtherKeyOb, OtherMemoryBlock);
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+
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+ return MyValue.Equals(OtherValue) ? EBlackboardCompare::Equal : EBlackboardCompare::NotEqual;
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+}
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+```
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+
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+为了支持 `Arithmetic` 操作，比较值的大小是通过重写 `TestArithmeticOperation` 来实现的
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+
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+```cpp
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+bool UBlackboardKeyType_Int::TestArithmeticOperation(const UBlackboardComponent& OwnerComp, const uint8* MemoryBlock, EArithmeticKeyOperation::Type Op, int32 OtherIntValue, float OtherFloatValue) const
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+{
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+ const int32 Value = GetValue(this, MemoryBlock);
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+ switch (Op)
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+ {
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+ case EArithmeticKeyOperation::Equal: return (Value == OtherIntValue);
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+ case EArithmeticKeyOperation::NotEqual: return (Value != OtherIntValue);
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+ case EArithmeticKeyOperation::Less: return (Value < OtherIntValue);
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+ case EArithmeticKeyOperation::LessOrEqual: return (Value <= OtherIntValue);
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+ case EArithmeticKeyOperation::Greater: return (Value > OtherIntValue);
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+ case EArithmeticKeyOperation::GreaterOrEqual: return (Value >= OtherIntValue);
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+ default: break;
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+ }
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+
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+ return false;
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+}
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+```
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+
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+为了支持 `Text` 操作，字符串处理是通过重写 `TestTextOperation` 函数来实现的
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+
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+```cpp
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+bool UBlackboardKeyType_Name::TestTextOperation(const UBlackboardComponent& OwnerComp, const uint8* MemoryBlock, ETextKeyOperation::Type Op, const FString& OtherString) const
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+{
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+ const FString Value = GetValue(this, MemoryBlock).ToString();
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+ switch (Op)
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+ {
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+ case ETextKeyOperation::Equal: return (Value == OtherString);
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+ case ETextKeyOperation::NotEqual: return (Value != OtherString);
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+ case ETextKeyOperation::Contain: return (Value.Contains(OtherString) == true);
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+ case ETextKeyOperation::NotContain: return (Value.Contains(OtherString) == false);
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+ default: break;
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+ }
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+
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+ return false;
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+}
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+```
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