簡體   English   中英

以看似隨機的間隔獲取NullPointerException,不知道為什么

[英]Getting a NullPointerException at seemingly random intervals, not sure why

我正在從Kinect庫中運行一個示例以進行處理(http://www.shiffman.net/2010/11/14/kinect-and-processing/),有時會得到一個NullPointerException指向此行:

  int rawDepth = depth[offset];

深度數組在以下行中創建:

  int[] depth = kinect.getRawDepth();

我不確定NullPointerException是什么,並且很多谷歌搜索並沒有真正幫助。 對我來說,代碼編譯70%的時間並意外地返回錯誤似乎使我感到奇怪。 硬件本身會影響它嗎?

這是整個示例,如果有幫助的話:

// Daniel Shiffman
// Kinect Point Cloud example
// http://www.shiffman.net
// https://github.com/shiffman/libfreenect/tree/master/wrappers/java/processing

import org.openkinect.*;
import org.openkinect.processing.*;

// Kinect Library object
Kinect kinect;

float a = 0;

// Size of kinect image
int w = 640;
int h = 480;


// We'll use a lookup table so that we don't have to repeat the math over and over
float[] depthLookUp = new float[2048];

void setup() {
  size(800,600,P3D);
  kinect = new Kinect(this);
  kinect.start();
  kinect.enableDepth(true);
  // We don't need the grayscale image in this example
  // so this makes it more efficient
  kinect.processDepthImage(false);

  // Lookup table for all possible depth values (0 - 2047)
  for (int i = 0; i < depthLookUp.length; i++) {
    depthLookUp[i] = rawDepthToMeters(i);
  }
}

void draw() {

  background(0);
  fill(255);
  textMode(SCREEN);
  text("Kinect FR: " + (int)kinect.getDepthFPS() + "\nProcessing FR: " + (int)frameRate,10,16);

  // Get the raw depth as array of integers
  int[] depth = kinect.getRawDepth();
  // We're just going to calculate and draw every 4th pixel (equivalent of 160x120)
  int skip = 4;

  // Translate and rotate
  translate(width/2,height/2,-50);
  rotateY(a);

  for(int x=0; x<w; x+=skip) {
    for(int y=0; y<h; y+=skip) {
      int offset = x+y*w;
      // Convert kinect data to world xyz coordinate
      int rawDepth = depth[offset];
      PVector v = depthToWorld(x,y,rawDepth);

      stroke(255);
      pushMatrix();
      // Scale up by 200
      float factor = 200;
      translate(v.x*factor,v.y*factor,factor-v.z*factor);
      // Draw a point
      point(0,0);
      popMatrix();
    }
  }

  // Rotate
  a += 0.015f;
}

// These functions come from: http://graphics.stanford.edu/~mdfisher/Kinect.html
float rawDepthToMeters(int depthValue) {
  if (depthValue < 2047) {
    return (float)(1.0 / ((double)(depthValue) * -0.0030711016 + 3.3309495161));
  }
  return 0.0f;
}

PVector depthToWorld(int x, int y, int depthValue) {

  final double fx_d = 1.0 / 5.9421434211923247e+02;
  final double fy_d = 1.0 / 5.9104053696870778e+02;
  final double cx_d = 3.3930780975300314e+02;
  final double cy_d = 2.4273913761751615e+02;

  PVector result = new PVector();
  double depth =  depthLookUp[depthValue];//rawDepthToMeters(depthValue);
  result.x = (float)((x - cx_d) * depth * fx_d);
  result.y = (float)((y - cy_d) * depth * fy_d);
  result.z = (float)(depth);
  return result;
}

void stop() {
  kinect.quit();
  super.stop();
}

這是錯誤:

processing.app.debug.RunnerException: NullPointerException
    at processing.app.Sketch.placeException(Sketch.java:1543)
    at processing.app.debug.Runner.findException(Runner.java:583)
    at processing.app.debug.Runner.reportException(Runner.java:558)
    at processing.app.debug.Runner.exception(Runner.java:498)
    at processing.app.debug.EventThread.exceptionEvent(EventThread.java:367)
    at processing.app.debug.EventThread.handleEvent(EventThread.java:255)
    at processing.app.debug.EventThread.run(EventThread.java:89)
Exception in thread "Animation Thread" java.lang.NullPointerException
    at org.openkinect.processing.Kinect.enableDepth(Kinect.java:70)
    at PointCloud.setup(PointCloud.java:48)
    at processing.core.PApplet.handleDraw(PApplet.java:1583)
    at processing.core.PApplet.run(PApplet.java:1503)
    at java.lang.Thread.run(Thread.java:637)

由於depth數組的值為null,因此您將獲得NullPointerException。 您可以從Kinect類的源代碼中看到,getRawDepth()方法有可能返回空值。 當時可能沒有圖像顯示。

可以在以下位置找到該代碼:

https://github.com/shiffman/libfreenect/blob/master/wrappers/java/processing/KinectProcessing/src/org/openkinect/processing/Kinect.java

您的代碼應在嘗試處理depth數組之前檢查是否為null。 例如...

int[] depth = kinect.getRawDepth();

if (depth == null) {
  // do something here where you handle there being no image
} else {
  // We're just going to calculate and draw every 4th pixel (equivalent of 160x120)
  int skip = 4;

  // Translate and rotate
  translate(width/2,height/2,-50);
  rotateY(a);

  for(int x=0; x<w; x+=skip) {
    for(int y=0; y<h; y+=skip) {
      int offset = x+y*w;
      // Convert kinect data to world xyz coordinate
      int rawDepth = depth[offset];
      PVector v = depthToWorld(x,y,rawDepth);

      stroke(255);
      pushMatrix();
      // Scale up by 200
      float factor = 200;
      translate(v.x*factor,v.y*factor,factor-v.z*factor);
      // Draw a point
      point(0,0);
      popMatrix();
    }
  }

  // Rotate
  a += 0.015f;
}

我建議使用Java調試器,以便在引發異常時可以看到變量的狀態。 有些人還喜歡使用log語句在應用程序的不同位置輸出變量的值。

然后,您可以將問題追溯到其中一個值未填充非空值的情況。

當offset> kinect.getRawDepth();時,將發生空指針。

您在這里有很多代碼,我將不介紹所有內容。 為什么可以假設offset為<kinect.getRawDepth()?

編輯

第二點,@ Asaph的評論可能是正確的。

depth[offset]不存在或尚未分配時,將發生空指針異常。 檢查depth[offset]是否未定義,這是nullpointer異常的原因。

檢查何時kinect.getRawDepth(); 大於offset

暫無
暫無

聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.

 
粵ICP備18138465號  © 2020-2024 STACKOOM.COM