[游戏开发]UE4 C++下实现按住左键持续开火

首先我们有一个以character为基类的角色类AShooterCharacter。角色类中已有一个FireWeapon函数实现在游戏内开火。这个函数在每次按下鼠标左键时会被调用一次，类似于半自动步枪。接下来要实现按住开火，松开停火。

最快速简单的实现如下

//在SetupPlayerInputComponent内绑定
	PlayerInputComponent->BindAction("FireButton", IE_Pressed, this, &AShooterCharacter::FireButtonPressed);
	PlayerInputComponent->BindAction("FireButton", IE_Released, this, &AShooterCharacter::FireButtonReleased);
//在AShooterCharacter.h内定义 FTimerHandle类AutoFireTimer和射击间隔AutomaticFireRate

void AShooterCharacter::FireButtonPressed()
{   //设置Timer循环调用FireWeapon
	GetWorldTimerManager().SetTimer(AutoFireTimer, this,
			&AShooterCharacter::FireWeapon,AutomaticFireRate,true);
}

void AShooterCharacter::FireButtonReleased()
{   //清空AutoFireTimer设定的Timer
	GetWorldTimerManager().ClearTimer(AutoFireTimer);
}

这个方法利用UE4的Timer功能实现自动按一定间隔循环开枪直至松开左键。但是实际游戏中存在着各种角色无法开枪的可能，例如死亡，子弹耗尽，收到某些效果射速改变或不让开枪。上面的方法即不利于实现上述的效果也不方便由蓝图去操作。所以应设置一个布尔变量bShouldFire表示是否能继续开枪，再定义一个布尔变量bFireButtonPressed检测鼠标左键状态，两者共同决定是否开枪。

//在SetupPlayerInputComponent内绑定
	PlayerInputComponent->BindAction("FireButton", IE_Pressed, this, &AShooterCharacter::FireButtonPressed);
	PlayerInputComponent->BindAction("FireButton", IE_Released, this, &AShooterCharacter::FireButtonReleased);

void AShooterCharacter::FireButtonPressed()
{
	bFireButtonPressed = true;
	StartFireTimer();
}

void AShooterCharacter::FireButtonReleased()
{
	bFireButtonPressed = false;
}

void AShooterCharacter::StartFireTimer()
{
	if (bShouldFire)
	{
		FireWeapon();
		bShouldFire = false;
		GetWorldTimerManager().SetTimer(AutoFireTimer, this,
			&AShooterCharacter::AutoFireReset,AutomaticFireRate);
	}
}

void AShooterCharacter::AutoFireReset()
{
	bShouldFire = true;
	if (bFireButtonPressed)
	{
		StartFireTimer();
	}
}

StartFireTimer()和AutoFireReset()相互调用来实现循环开枪，只用修改bShouldFire就能阻止角色继续开火，而不是调用GetWorldTimerManager().ClearTimer(AutoFireTimer)来使角色停火。例如玩家开枪时枪射速变慢，原本要先ClearTimer再SetTimer，现在只用修改AutomaticFireRate的值即可，对外部蓝图实现效果也更方便。