博客来源于: https://blog.csdn.net/panda1234lee/article/details/64123532
3. 创建带参数的委托
我们可以通过修改委托的签名来使其接受参数
比如我们需要接受一个参数的话,可以在 GameMode 中这样声明:
- DECLARE_DELEGATE_OneParam(FParamDelegateSignature, FLinearColor)
注意:这个宏与之前稍有不同,后缀多出了一个 _OneParam ,而且我们还需要指定接受参数的类型——本例为 FLinearColor
- FParamDelegateSignature MyParameterDelegate;
这和之前一样,创建一个委托实例作为 GameMode 成员
然后创建一个 Actor 类,取名为 ParamDelegateListener,
在头文件中添加以下声明
- UFUNCTION()
- void SetLightColor(FLinearColor LightColor);
- UPROPERTY()
- UPointLightComponent* PointLight;
ParamDelegateListener.cpp
- #include "Test.h"
- #include "UE4TestGameMode.h"
- #include "ParamDelegateListener.h"
- // Sets default values
- AParamDelegateListener::AParamDelegateListener()
- {
- // Set this actor to call Tick() every frame. You can turn this off to improve performance if you don't need it.
- PrimaryActorTick.bCanEverTick = true;
- PointLight = CreateDefaultSubobject<UPointLightComponent>("PointLight");
- RootComponent = PointLight;
- }
- // Called when the game starts or when spawned
- void AParamDelegateListener::BeginPlay()
- {
- Super::BeginPlay();
- UWorld* TheWorld = GetWorld();
- if (TheWorld != nullptr)
- {
- AGameMode* GameMode = Cast<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
- AUE4TestGameMode * MyGameMode = Cast<AUE4TestGameMode>(GameMode);
- if (MyGameMode != nullptr)
- {
- // Binds a UObject-based member function delegate. UObject delegates keep a weak reference to your object. You can use ExecuteIfBound() to call them.(注意绑定的还是 UFUNCTION)
- MyGameMode->MyParameterDelegate.BindUObject(this, &AParamDelegateListener::SetLightColor);
- }
- }
- }
- // Called every frame
- void AParamDelegateListener::Tick( float DeltaTime )
- {
- Super::Tick( DeltaTime );
- }
- // 1个参数
- void AParamDelegateListener::SetLightColor(FLinearColor LightColor)
- {
- PointLight->SetLightColor(LightColor);
- }
回到 MyTriggerVollume.cpp,在 NotifyActorBeginOverlap 函数中添加以下代码:
- MyGameMode->MyParameterDelegate.ExecuteIfBound(FLinearColor(1, 0, 0, 1)); // 带一个参数
与之前不同的是,我们需要多指定一个参数,参数类型和我们之前的委托声明一致。
显然,MyTriggerVolume 压根就无需知道 ParamDelegateListener 的存在,却通过 GameMode 就可以调用 ParamDelegateListener 的函数了,很大程度上降低了类间的耦合度。
解绑委托方式与之前相同,不再赘述。
4.通过委托绑定传递负载数据(Payload Data)
稍加修改,我们就可以在委托被调用时传递额外创建时的参数(additional creation-time parameter),即我们在 MyTriggerVolume 中的调用方式不变,仍然是 ExecuteIfBound(FLinearColor(1, 0, 0, 1)),但可以额外添加一些负载数据,在 ParamDelegateListener 中的 BindUObject 上添加。
首先修改 AParamDelegateListener::BeginPlay 中的 BindUObject,为其添加一个 bool 负载数据
- MyGameMode->MyParameterDelegate.BindUObject(this, &AParamDelegateListener::SetLightColor, false);
并修改 SetLightColor 的定义
- UFUNCTION()
- void SetLightColor(FLinearColor LightColor, bool EnableLight);
- // 2个参数
- void AParamDelegateListener::SetLightColor(FLinearColor LightColor, bool EnableLight)
- {
- PointLight->SetLightColor(LightColor);
- PointLight->SetVisibility(EnableLight);
- }
注意:负载数据并不局限于带参数的委托,其他的委托形式也可以使用
5. 多播委托(Multicast Delegate)
之前说的委托,都是只绑定了一个函数指针,而多播委托绑定的是一个函数指针集合,每个函数指针都有对应的一个委托句柄,当广播(Broadcast)委托的时候,他们将会被激活。
首先在 GameMode 中添加多播的委托声明
需要明确声明为多播
- DECLARE_MULTICAST_DELEGATE(FMulticastDelegateSignature)
接着在类中声明一个 FMulticastDelegateSignature 成员
- FMulticastDelegateSignature MyMulticastDelegate;
其次,创建一个新 Actor 类,命名为 MulticastDelegateListener
在其头文件中添加以下声明:
- FDelegateHandle MyDelegateHandle;
- UPROPERTY()
- UPointLightComponent* PointLight;
- UFUNCTION()
- void ToggleLight();
- virtual void EndPlay(const EEndPlayReason::Type EndPlayReason) override;
大部分和之前的 Listener 类很相似,但是多一个 委托句柄实例,将用它来存储委托实例的引用,我们的添加(AddUObject)和移除(Remove)都需要它作为参数
源文件的代码如下:
- // Sets default values
- AMulticastDelegateListener::AMulticastDelegateListener()
- {
- // Set this actor to call Tick() every frame. You can turn this off to improve performance if you don't need it.
- PrimaryActorTick.bCanEverTick = true;
- PointLight = CreateDefaultSubobject<UPointLightComponent>("PointLight");
- RootComponent = PointLight;
- }
- // Called when the game starts or when spawned
- void AMulticastDelegateListener::BeginPlay()
- {
- Super::BeginPlay();
- UWorld* TheWorld = GetWorld();
- if (TheWorld != nullptr)
- {
- AGameMode* GameMode = Cast<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
- AUE4TestGameMode * MyGameMode = Cast<AUE4TestGameMode>(GameMode);
- if (MyGameMode != nullptr)
- {
- // Adds a UObject-based member function delegate. UObject delegates keep a weak reference to your object.
- // 注册一个对象方法
- MyDelegateHandle = MyGameMode->MyMulticastDelegate.AddUObject(this, &AMulticastDelegateListener::ToggleLight);
- }
- }
- }
- // Called every frame
- void AMulticastDelegateListener::Tick( float DeltaTime )
- {
- Super::Tick( DeltaTime );
- }
- void AMulticastDelegateListener::ToggleLight()
- {
- PointLight->ToggleVisibility();
- }
- void AMulticastDelegateListener::EndPlay(const EEndPlayReason::Type EndPlayReason)
- {
- Super::EndPlay(EndPlayReason);
- UWorld* TheWorld = GetWorld();
- if (TheWorld != nullptr)
- {
- AGameMode* GameMode = Cast<AGameMode>(UGameplayStatics::GetGameMode(TheWorld));
- AUE4TestGameMode * MyGameMode = Cast<AUE4TestGameMode>(GameMode);
- if (MyGameMode != nullptr)
- {
- // Removes a function from this multi-cast delegate's invocation list (performance is O(N)). Note that the order of the delegates may not be preserved!
- MyGameMode->MyMulticastDelegate.Remove(MyDelegateHandle);
- }
- }
- }
MyTriggerVolume.cpp 的实现为:
- // Broadcasts this delegate to all bound objects, except to those that may have expired.
- MyGameMode->MyMulticastDelegate.Broadcast();
广播函数很像我们之前的 ExecuteIfBound函数,但有一点不同,它不需要检查是否有函数绑定在委托上。
最后的效果是,如果我们往场景中拖放了四五个MulticastDelegateListener,当我们进入触发区域,它们的灯会同时打开或关闭,因为每个实例函数都被添加到委托集合当中;
如果拖放了四五个DelegateListener 到场景中,当我们进入触发区域,只有最后一个拖进场景的灯会亮,这是因为委托只绑定了最后一个实例函数。
(未完待续)