Possible bug in Unity3D?

Question

显然，在 Unity3D 更新后，我无法再从一个场景切换到另一个场景。我不知道这是否是由于更新造成的问题，但目前，当我单击一个应该将我送回另一个场景的按钮时，我收到此错误。

ArgumentException: method return type is incompatible
System.Delegate.CreateDelegate (System.Type type, System.Object firstArgument, System.Reflection.MethodInfo method, Boolean throwOnBindFailure) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Delegate.cs:190)
System.Delegate.CreateDelegate (System.Type type, System.Object firstArgument, System.Reflection.MethodInfo method) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Delegate.cs:276)
UnityEngineInternal.NetFxCoreExtensions.CreateDelegate (System.Reflection.MethodInfo self, System.Type delegateType, System.Object target) (at /Users/builduser/buildslave/unity/build/Runtime/Export/WinRT/NetFxCoreExtensions.cs:11)
UnityEngine.Events.InvokableCall..ctor (System.Object target, System.Reflection.MethodInfo theFunction) (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent.cs:149)
UnityEngine.Events.PersistentCall.GetRuntimeCall (UnityEngine.Events.UnityEventBase theEvent) (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent.cs:447)
UnityEngine.Events.PersistentCallGroup.Initialize (UnityEngine.Events.InvokableCallList invokableList, UnityEngine.Events.UnityEventBase unityEventBase) (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent.cs:610)
UnityEngine.Events.UnityEventBase.RebuildPersistentCallsIfNeeded () (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent.cs:776)
UnityEngine.Events.UnityEventBase.PrepareInvoke () (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent.cs:812)
UnityEngine.Events.UnityEvent.Invoke () (at /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:53)
UnityEngine.UI.Button.Press () (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update()

目前该错误发生在2018.1.0f2版本上，不幸的是我不记得之前使用的版本了。

这是与负责场景切换的脚本相关的代码，效果很好：

using UnityEngine.SceneManagement;
using UnityEngine;

public class MainEngine : MonoBehaviour {

    // Use this for initialization
    void Start () {
        DontDestroyOnLoad(this.gameObject);
        SceneManager.activeSceneChanged += ChangedActiveScene;
        SceneManager.LoadScene("Introduction");
    }

    // Update is called once per frame
    void Update () {

    }

    private void ChangedActiveScene(Scene current, Scene next)
    {
        string currentName = current.name;

        if (currentName == null)
        {
            // Scene1 has been removed
            currentName = "Replaced";
        }

        Debug.Log("Scenes: " + currentName + ", " + next.name);
    }
}

但以下是“有罪”代码：

using UnityEngine.SceneManagement;
using UnityEngine;
using System.Collections;

public class InstructionsScene : MonoBehaviour {

    IEnumerator PlayNow()
    {
        Debug.Log("scene should be changed");

        float fadeTime = GameObject.Find("SceneEngine").GetComponent<Fading>().BeginFade(1);
        yield return new WaitForSeconds(fadeTime);
        SceneManager.LoadScene("Instructions", LoadSceneMode.Single);      
    }

}

Answer 1

按钮（通常可能是 UI 元素）的回调必须是return type void. 你的是return type IEnumerator（如果PlayNow是你从按钮调用的函数）。

解决方法是从内部启动协程PlayNow：

public void PlayNow()
{
    Debug.Log("scene should be changed");

    StartCoroutine(PlayNowCoroutine());
}

IEnumerator PlayNowCoroutine()
{
    float fadeTime = GameObject.Find("SceneEngine").GetComponent<Fading>().BeginFade(1);
    yield return new WaitForSeconds(fadeTime);
    SceneManager.LoadScene("Instructions", LoadSceneMode.Single); 
}