單擊呼叫不使用索引的函式的按鈕時引數超出范圍例外

目前正在撰寫一個構建 HUD 的腳本，用于測驗專案中的某些功能。它會自動構建按鈕，其中一個有效，而另一個給出標題中指示的錯誤和下面的錯誤訊息。

當被手動放置在場景中的按鈕呼叫時，按鈕呼叫的函式起作用，這表明問題不在于函式本身，而在于按鈕的構建方式。

腳本編譯成功并在編輯器中正確呈現。單擊單選按鈕（構建給出錯誤的按鈕）可以正常作業，構建按鈕并運行除錯日志。

單擊單選按鈕生成的“下一首歌曲”按鈕時會發生錯誤。

這是錯誤：

ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
System.Collections.Generic.List`1[T].get_Item (System.Int32 index) (at <6073cf49ed704e958b8a66d540dea948>:0)
TestHUD <>c__DisplayClass12_0.<BuildActions>b__0 () (at Assets/Scripts/TestHUD.cs:86)
UnityEngine.Events.InvokableCall.Invoke () (at <f1212ad1dec44ce7b7147976b91869c3>:0)
UnityEngine.Events.UnityEvent.Invoke () (at <f1212ad1dec44ce7b7147976b91869c3>:0)
UnityEngine.UI.Button.Press () (at Library/PackageCache/[email protected]/Runtime/UI/Core/Button.cs:70)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at Library/PackageCache/[email protected]/Runtime/UI/Core/Button.cs:114)
UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at Library/PackageCache/[email protected]/Runtime/EventSystem/ExecuteEvents.cs:57)
UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents EventFunction`1[T1] functor) (at Library/PackageCache/[email protected]/Runtime/EventSystem/ExecuteEvents.cs:272)
UnityEngine.EventSystems.EventSystem:Update() (at Library/PackageCache/[email protected]/Runtime/EventSystem/EventSystem.cs:501)

這是除錯日志

buttonActions 的長度為 1。

創建的功能按鈕

這是當前存在的腳本：

using System;
using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.UI;

public class TestHUD : MonoBehaviour
{
    GameObject testHUD;

    public List<TestHUDPanel> testHUDPanels = new();

    public GameObject sectionPanel;
    public GameObject functionPanel;

    public GameObject sectionPrefab;
    public GameObject functionPrefab;

    //Color32 activeColor = new Color32(255, 201, 191, 255);
    //Color32 inactiveColor = new Color32(191, 255, 241, 255);

    SoundManager soundManager;

    public class TestHUDPanel
    {
        public string name;
        public GameObject linkedObject;
        public GameObject panelObject;
        public List<Action> buttonActions = new();
        public List<string> buttonLabels = new();

        public TestHUDPanel(string panelName)
        {
            name = panelName;
        }

        public void AddButton(string buttonName, Action buttonFunc)
        {
            buttonActions.Add(buttonFunc);
            buttonLabels.Add(buttonName);
        }
    }

    private void Awake()
    {
        testHUD = gameObject;
        soundManager = GameObject.Find("SoundManager").GetComponent<SoundManager>();
    }

    private void Start()
    {
        BuildPanelList();
        BuildPanels();
    }

    public void BuildPanelList()
    {
        testHUDPanels.Add(new TestHUDPanel("Radio"));
        testHUDPanels[0].AddButton("Next Song", soundManager.PlayNextSong);
        testHUDPanels.Add(new TestHUDPanel("Typing"));
        testHUDPanels.Add(new TestHUDPanel("Audio"));
    }


    public void BuildPanels()
    {
        foreach (TestHUDPanel panel in testHUDPanels)
        {
            GameObject panelObject = Instantiate(sectionPrefab);
            panelObject.transform.SetParent(sectionPanel.transform);
            Button button = panelObject.GetComponent<Button>();
            panelObject.GetComponentInChildren<TextMeshProUGUI>().text = panel.name;
            button.onClick.AddListener(() => BuildActions(panel));
        }
    }

    public void BuildActions(TestHUDPanel panel)
    {
        for (int i = 0; i < panel.buttonActions.Count; i  )
        {
            GameObject panelObject = Instantiate(functionPrefab);
            panelObject.transform.SetParent(functionPanel.transform);
            Button button = panelObject.GetComponent<Button>();
            panelObject.GetComponentInChildren<TextMeshProUGUI>().text = panel.buttonLabels[i];
            Debug.Log(string.Format("Length of buttonActions is {0}, ", panel.buttonActions.Count));
            >>> THIS IS LINE 86 <<< : button.onClick.AddListener(() => panel.buttonActions[i]());
            Debug.Log("Function button created");
        }
    }
}

uj5u.com熱心網友回復：

正如漢斯指出的那樣，問題源于一個捕獲的變數。

當我們的變數向上迭代時，lambda 運算式沒有正確捕獲它，因此給出了上面提到的錯誤。

下面是更新后的 BuildActions 函式，其中有一個臨時變數，它臨時保存 i 的值以允許它在 lambda 運算式中使用，即使迭代器在賦值和執行之間更改值，臨時變數仍將允許 lambda 運算式正常運行。

public void BuildActions(TestHUDPanel panel)
{
    for (int i = 0; i < panel.buttonActions.Count; i  )
    {
        var tempIDX = i;
        GameObject panelObject = Instantiate(functionPrefab);
        panelObject.transform.SetParent(functionPanel.transform);
        Button button = panelObject.GetComponent<Button>();
        panelObject.GetComponentInChildren<TextMeshProUGUI>().text = panel.buttonLabels[i];
        button.onClick.AddListener(() => panel.buttonActions[tempIDX]());
    }
}

我還將鏈接 lambda 運算式中捕獲的變數的檔案以進行進一步解釋。

捕獲 lambda 運算式中的外部變數和變數范圍

標籤：unity3d 用户界面 按钮

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