Question

我正在做游戏，我有一个带有开始按钮的主菜单，该按钮工作得很好。唯一的问题是您可以看到背景，所以我添加了另一个名为“ fadeImage”的图像，因此我想拥有它，因此只要负责检测单击按钮的功能，淡出名为“ fadeImage”的图像。我尝试使用GetComponent和GetGameObject，每当我使用CrossFade Alpha时，在第51行都会收到错误Object reference not set to instance of object。这是我的代码

using UnityEngine;
using System.Collections;
using UnityEngine.Audio;
using UnityEngine.SceneManagement;
using UnityEngine.UI;


public class StartOptions : MonoBehaviour 
{
    public int sceneToStart = 1;                                        //Index number in build settings of scene to load if changeScenes is true
    public bool changeScenes;                                           //If true, load a new scene when Start is pressed, if false, fade out UI and continue in single scene
    public bool changeMusicOnStart;                                     //Choose whether to continue playing menu music or start a new music clip
    public Image fadeImage;

    [HideInInspector] public bool inMainMenu = true;                    //If true, pause button disabled in main menu (Cancel in input manager, default escape key)
    [HideInInspector] public Animator animColorFade;                    //Reference to animator which will fade to and from black when starting game.
    [HideInInspector] public Animator animMenuAlpha;                    //Reference to animator that will fade out alpha of MenuPanel canvas group
     public AnimationClip fadeColorAnimationClip;       //Animation clip fading to color (black default) when changing scenes
    [HideInInspector] public AnimationClip fadeAlphaAnimationClip;      //Animation clip fading out UI elements alpha

    private PlayMusic playMusic;                                        //Reference to PlayMusic script
    private float fastFadeIn = .01f;                                    //Very short fade time (10 milliseconds) to start playing music immediately without a click/glitch
    private ShowPanels showPanels;                                      //Reference to ShowPanels script on UI GameObject, to show and hide panels

    void Awake()
    {
        //Get a reference to ShowPanels attached to UI object
        showPanels = GetComponent<ShowPanels> ();

        //Get a reference to PlayMusic attached to UI object
        playMusic = GetComponent<PlayMusic> ();

        fadeImage = GetComponent<Image>();       
    }

    public void StartButtonClicked()
    {
        //If changeMusicOnStart is true, fade out volume of music group of AudioMixer by calling FadeDown function of PlayMusic, using length of fadeColorAnimationClip as time. 
        //To change fade time, change length of animation "FadeToColor"
        fadeImage.CrossFadeAlpha(1.0f, 1.0f, true);

        if (changeMusicOnStart) 
        {
            playMusic.FadeDown(fadeColorAnimationClip.length);
        }

        //If changeScenes is true, start fading and change scenes halfway through animation when screen is blocked by FadeImage
        if (changeScenes) 
        {
            //Use invoke to delay calling of LoadDelayed by half the length of fadeColorAnimationClip
            Invoke ("LoadDelayed", fadeColorAnimationClip.length * .5f);

            //Set the trigger of Animator animColorFade to start transition to the FadeToOpaque state.
            animColorFade.SetTrigger ("fade");
        } 

        //If changeScenes is false, call StartGameInScene
        else 
        {
            //Call the StartGameInScene function to start game without loading a new scene.
            StartGameInScene();
        }
    }

    void OnEnable()
    {
        SceneManager.sceneLoaded += SceneWasLoaded;
    }

    void OnDisable()
    {
        SceneManager.sceneLoaded -= SceneWasLoaded;
    }

    //Once the level has loaded, check if we want to call PlayLevelMusic
    void SceneWasLoaded(Scene scene, LoadSceneMode mode)
    {
        //if changeMusicOnStart is true, call the PlayLevelMusic function of playMusic
        if (changeMusicOnStart)
        {
            playMusic.PlayLevelMusic ();
        }   
    }

    public void LoadDelayed()
    {
        //Pause button now works if escape is pressed since we are no longer in Main menu.
        inMainMenu = false;

        //Hide the main menu UI element
        showPanels.HideMenu ();

        //Load the selected scene, by scene index number in build settings
        SceneManager.LoadScene (sceneToStart);
    }

    public void HideDelayed()
    {
        //Hide the main menu UI element after fading out menu for start game in scene
        showPanels.HideMenu();
    }

    public void StartGameInScene()
    {
        //Pause button now works if escape is pressed since we are no longer in Main menu.
        inMainMenu = false;

        //If changeMusicOnStart is true, fade out volume of music group of AudioMixer by calling FadeDown function of PlayMusic, using length of fadeColorAnimationClip as time. 
        //To change fade time, change length of animation "FadeToColor"
        if (changeMusicOnStart) 
        {
            //Wait until game has started, then play new music
            Invoke ("PlayNewMusic", fadeAlphaAnimationClip.length);
        }
        //Set trigger for animator to start animation fading out Menu UI
        animMenuAlpha.SetTrigger ("fade");
        Invoke("HideDelayed", fadeAlphaAnimationClip.length);
        Debug.Log ("Game started in same scene! Put your game starting stuff here.");
    }

    public void PlayNewMusic()
    {
        //Fade up music nearly instantly without a click 
        playMusic.FadeUp (fastFadeIn);
        //Play music clip assigned to mainMusic in PlayMusic script
        playMusic.PlaySelectedMusic (1);
    }
}

无论何时我删除任何引用该图像的代码，“开始”按钮都将起作用，但是当我没有收到该错误时，“开始”按钮将保持蓝色，这应该是在鼠标悬停在其上方时发生的。

Answer 1

fadeImage = GetComponent<Image>();函数中的这一行Start仅在将此脚本附加到图像时才有效。这就是为什么出现空引用错误的原因，因为具有这种单行为的对象没有图像组件。

Answer 2

似乎

fadeImage = GetComponent<Image>();

仅会失败并返回null，因为此脚本所附加的Image上没有GameObject组件。

GetComponent如果游戏对象附加了一个，则返回Type类型的组件，否则返回null。

你说

我在按钮中添加了一个名为fadeImage的图像

所以我想说，您宁愿使用GetComponentInChildren在该脚本所附的Image下的下的层次结构中查找GameObject递归组件

// By passing a true as parameter you make also // Sure that the component will also be found // if it is currently not active or disabled - otherwise it would be ignored fadeImage = GetComponentInChildren<Image>(true);

每当我点击按钮时就淡化图像

2 个答案: