一、官網(wǎng)的Physics文檔

https://docs.unity.cn/cn/2019.4/ScriptReference/Physics.html

1、Physics下帶NonAlloc都是無GC的，項目中必須使用NonAlloc相關(guān)的函數(shù)來進(jìn)行物理檢測；

Physics.OverlapBox有GC，Physics.OverlapBoxNonAlloc無GC

GC對比.png

二、Physics.NonAlloc的幾個函數(shù)有時候生效有時候不生效問題

1、先看一下下面的測試代碼

public class ColliderTest : MonoBehaviour
{
    private Collider[] m_Colliders;

    void Update()
    {
        m_Colliders = Physics.OverlapBox(Vector3.zero, new Vector3(2, 2, 2));
        Debug.Log("OverlapBox：" + m_Colliders.Length);

        var count = Physics.OverlapBoxNonAlloc(Vector3.zero, new Vector3(2, 2, 2), m_Colliders);
        Debug.Log("OverlapBoxNonAlloc：" + count);
    }
}

結(jié)果都可以

成功.png

2、現(xiàn)在我們切換到項目中的無GC寫法的代碼中去

public class ColliderTest : MonoBehaviour
{
    private Collider[] m_Colliders;

   void Update()
    {
        var count = Physics.OverlapBoxNonAlloc(Vector3.zero, new Vector3(2, 2, 2), m_Colliders);
        Debug.Log("OverlapBoxNonAlloc：" + count);
    }
}

結(jié)果沒有任何輸出，失敗了，為什么？

失敗.png

三、問題探究解決

1、我們看下兩次代碼都有哪些變化

（1）成功：測試代碼的Physics.OverlapBox接收的Collider數(shù)組用的是m_Colliders

（2）成功：測試代碼的Physics.OverlapBoxNonAlloc參數(shù)也是用的m_Colliders

（3）失敗：測試代碼的Physics.OverlapBoxNonAlloc參數(shù)是用的m_Colliders

2、發(fā)現(xiàn)問題所在

（1）成功：m_Colliders數(shù)組默認(rèn)沒有初始化，Physics.OverlapBox接收的數(shù)組賦值給了m_Colliders，此時m_Colliders就被初始化了，當(dāng)Physics.OverlapBoxNonAlloc傳遞進(jìn)去的數(shù)組就已經(jīng)是初始化后的了，所以成功了；

（2）失?。簃_Colliders數(shù)組沒有被初始化，直接傳遞給了Physics.OverlapBoxNonAlloc的參數(shù)，Physics.OverlapBoxNonAlloc內(nèi)部并不會對一個沒有初始化的Collider[]進(jìn)行初始化，因為Collider[]初始化的長度由外部使用者決定的，所以使用Physics.NonAlloc相關(guān)的函數(shù)外部傳遞進(jìn)去的緩存數(shù)組必須先初始化

private Collider[] m_Colliders = new Collider[1];

2、問題解決

public class ColliderTest : MonoBehaviour
{
    private Collider[] m_Colliders = new Collider[1];

    void Update()
    {
        var count = Physics.OverlapBoxNonAlloc(Vector3.zero, new Vector3(2, 2, 2), m_Colliders);
        Debug.Log("OverlapBoxNonAlloc：" + count);
    }
}

成功.png