83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
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# BlueprintAutocast
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- **功能描述：** 告诉蓝图系统这个函数是用来支持从A类型到B类型的自动转换。
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- **使用位置：** UFUNCTION
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- **引擎模块：** Blueprint
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- **元数据类型：** bool
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- **常用程度：** ★
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告诉蓝图系统这个函数是用来支持从A类型到B类型的自动转换。
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所谓自动转换指的是从A类型的Pin拖拉到B类型的Pin时，蓝图会在其中自动的生成类型转换节点。
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这种转换函数必须是BlueprintPure，因为其实是被动调用的，不带主动执行节点。
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## 测试代码：
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```cpp
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USTRUCT(BlueprintType)
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struct FAutoCastFrom
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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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int32 X = 0;
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UPROPERTY(BlueprintReadWrite, EditAnywhere)
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int32 Y = 0;
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};
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USTRUCT(BlueprintType)
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struct FAutoCastTo
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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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int32 Sum = 0;
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};
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USTRUCT(BlueprintType)
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struct FNoAutoCastTo
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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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int32 Sum = 0;
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};
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyFunction_AutoCast :public UBlueprintFunctionLibrary
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{
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public:
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GENERATED_BODY()
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public:
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UFUNCTION(BlueprintPure, meta = (BlueprintAutocast))
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static FAutoCastTo Conv_MyTestAutoCast(const FAutoCastFrom& InValue);
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};
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//转换函数也经常配合CompactNodeTitle使用。
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UFUNCTION(BlueprintPure, Category="Widget", meta = (CompactNodeTitle = "->", BlueprintAutocast))
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static UMG_API FInputEvent GetInputEventFromKeyEvent(const FKeyEvent& Event);
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```
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## 示例效果：
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支持自动转换的FAutoCastTo就在拖拉连线的时候就会自动生成节点，而没有自动转换函数的FNoAutoCastTo就会产生报错。
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## 原理代码：
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从这可以看出，该函数必须是static，C++中的Public函数，标上BlueprintPure，拥有返回值，且有一个输入参数。引擎里类型的自动转换关系是靠FAutocastFunctionMap来维护的。
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```cpp
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static bool IsAutocastFunction(const UFunction* Function)
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{
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const FName BlueprintAutocast(TEXT("BlueprintAutocast"));
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return Function
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&& Function->HasMetaData(BlueprintAutocast)
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&& Function->HasAllFunctionFlags(FUNC_Static | FUNC_Native | FUNC_Public | FUNC_BlueprintPure)
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&& Function->GetReturnProperty()
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&& GetFirstInputProperty(Function);
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}
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```
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