Unity正常代码突发NullReferenceException异常求助

问题描述 #

原本可正常运行的Unity代码修改后突发异常，错误信息为：NullReferenceException: Object reference not set to an instance of an object，错误触发在代码第23行。

问题代码 #

using System;
using System.IO;
using UnityEngine;
using UnityEngine.Rendering;

public class SaveImage : MonoBehaviour {

    public static SaveImage Instance { get; private set; }

    [SerializeField] private Camera screenshotCamera;

    private Action<Texture2D> onScreenshotTaken;

    private void Awake() {
        Instance = this;
        RenderPipelineManager.endFrameRendering += RenderPipelineManager_endFrameRendering;
    }

    private void RenderPipelineManager_endFrameRendering(ScriptableRenderContext arg1, Camera[] arg2) {
        if (onScreenshotTaken != null) {
            RenderTexture renderTexture = screenshotCamera.targetTexture;

            Texture2D renderResult = new Texture2D(renderTexture.width, renderTexture.height, TextureFormat.ARGB32, false);
            Rect rect = new Rect(0, 0, renderTexture.width, renderTexture.height);
            renderResult.ReadPixels(rect, 0, 0);
            renderResult.Apply();

            RenderTexture.ReleaseTemporary(renderTexture);
            screenshotCamera.targetTexture = null;

            onScreenshotTaken(renderResult);
            onScreenshotTaken = null;

            Destroy(renderResult);
        }
    }

    public void Save() {

       TakeScreenshot(Screen.width, Screen.height, (Texture2D screenshotTexture) => {
            string pathfile = Application.persistentDataPath + "/NGallery/ImageData.png";
            string imagestorage = pathfile;
            byte[] screenshotByteArray = screenshotTexture.EncodeToPNG();
            File.WriteAllBytes(imagestorage, screenshotByteArray);
        });
    }

    private void TakeScreenshot(int width, int height, Action<Texture2D> onScreenshotTaken) {
        screenshotCamera.targetTexture = RenderTexture.GetTemporary(width, height, 16);
        this.onScreenshotTaken = onScreenshotTaken;
    }
}

已尝试操作及结果 #

• 加载旧Unity项目：运行正常
• 重新创建项目：触发错误
• 复制旧项目：触发错误
• 新项目中Debug.Log(renderTexture)显示该对象为null
• 旧项目中Debug.Log(renderTexture)显示该对象不为null且正常运行

解决方案 #

问题根源 #

第23行报错是因为renderTexture为null，核心原因有两个：

1. 事件触发时机不匹配：新项目若使用URP/HDRP管线，RenderPipelineManager.endFrameRendering可能在TakeScreenshot设置相机目标纹理前就触发，或者事件每帧执行，第二次执行时纹理已被释放。
2. 缺少必要的null校验：代码未判断screenshotCamera或renderTexture是否为null，一旦引用丢失或未初始化就会报错。

修复步骤 #

1. 增加全链路Null校验

在使用关键对象前添加null判断，避免直接访问空对象属性：

private void RenderPipelineManager_endFrameRendering(ScriptableRenderContext arg1, Camera[] arg2) {
    // 增加screenshotCamera和renderTexture的null校验
    if (onScreenshotTaken != null && screenshotCamera != null && screenshotCamera.targetTexture != null) {
        RenderTexture renderTexture = screenshotCamera.targetTexture;
        // 后续原有代码保持不变
    }
}

2. 避免重复请求截图

防止同一帧内多次调用TakeScreenshot导致的状态混乱：

private void TakeScreenshot(int width, int height, Action<Texture2D> onScreenshotTaken) {
    // 如果已有待处理的截图请求，直接返回
    if (this.onScreenshotTaken != null) return;
    screenshotCamera.targetTexture = RenderTexture.GetTemporary(width, height, 16);
    this.onScreenshotTaken = onScreenshotTaken;
}

3. 适配SRP管线的正确事件（推荐）

放弃全局的endFrameRendering事件，改为监听目标截图相机的渲染完成事件，确保只在相机渲染结束后执行截图逻辑：

private void Awake() {
    Instance = this;
    // 替换原事件注册，改为监听目标相机的PostRender事件
    if (screenshotCamera != null) {
        screenshotCamera.onPostRender += OnScreenshotCameraPostRender;
    }
}

private void OnScreenshotCameraPostRender() {
    if (onScreenshotTaken != null && screenshotCamera.targetTexture != null) {
        RenderTexture renderTexture = screenshotCamera.targetTexture;
        Texture2D renderResult = new Texture2D(renderTexture.width, renderTexture.height, TextureFormat.ARGB32, false);
        Rect rect = new Rect(0, 0, renderTexture.width, renderTexture.height);
        renderResult.ReadPixels(rect, 0, 0);
        renderResult.Apply();

        RenderTexture.ReleaseTemporary(renderTexture);
        screenshotCamera.targetTexture = null;

        onScreenshotTaken(renderResult);
        onScreenshotTaken = null;

        Destroy(renderResult);
    }
}

// 记得在销毁时移除事件监听，避免内存泄漏
private void OnDestroy() {
    if (screenshotCamera != null) {
        screenshotCamera.onPostRender -= OnScreenshotCameraPostRender;
    }
}

4. 检查相机引用

确保在Inspector面板中，SaveImage脚本的screenshotCamera字段已正确拖入场景中的相机对象，且该相机的Target Texture初始状态为null。

内容的提问来源于stack exchange，提问作者Zelkey