JNI DETECTED ERROR IN APPLICATION: jarray was NULL

项目中用到了opengles去展示三维点云数据，个人比较生疏，所以打算学一学。根据官方的示例先画了一个三角形，后面在画方形的时候怎么都不成功，报错:JNI DETECTED ERROR IN APPLICATION: jarray was NULL。可是对比别人的代码和自己的代码，根本看不出有什么区别，从别人的博客中看到以下内容:

在Java中当我们要对数据进行更底层的操作时，一般是操作数据的字节（byte）形式，这时经常会用到
ByteBuffer这样一个类。ByteBuffer提供了两种静态实例方式：public static ByteBuffer allocate(int capacity)  public static ByteBuffer allocateDirect(int capacity)
为什么要提供两种方式呢？这与Java的内存使用机制有关。第一种分配方式产生的内存开销是在JVM中的，
而另外一种的分配方式产生的开销在JVM之外，以就是系统级的内存分配。当Java程序接收到外部传来的数据时，
首先是被系统内存所获取，然后在由系统内存复制复制到JVM内存中供Java程序使用。所以在另外一种分配方式
中，能够省去复制这一步操作，效率上会有所提高。可是系统级内存的分配比起JVM内存的分配要耗时得多，所以
并非不论什么时候allocateDirect的操作效率都是最高的

前面在写三角形之前已经了解到了，opengles是不能直接使用java jvm分配的内存的，要将数组转换到系统内存才能使用，

我的示例里面因为用了这个所以一直报数组是空的

改成这样，方形就绘制出来了。

三角形和方形源码

public class Triangle {private FloatBuffer vertextBuffer;//number of coordinates per vertex in this array//每个顶点的坐标包括x,y,z 三个static final int COORDS_PER_VERTEXT = 3;//顺时针的顺序static float triangleCoords[] = {   // in counterclockwise order:0.0f, 0.622008459f, 0.0f, // top-0.5f, -0.311004243f, 0.0f, // bottom left0.5f, -0.311004243f, 0.0f  // bottom right};// Set color with red, green, blue and alpha (opacity) valuesfloat color[] = {0.63671875f, 0.76953125f, 0.22265625f, 1.0f};//1.为顶点在native层分配缓冲区内存，然后将顶点坐标放进缓冲区//2.绘制需要顶点着色器和片段着色器//绘制形状需要一个顶点着色程序和一个片段着色程序private final String vertexShaderCode ="attribute vec4 vPosition;" +"void main() {" +"  gl_Position = vPosition;" +"}";private final String fragmentShaderCode ="precision mediump float;" +"uniform vec4 vColor;" +"void main() {" +"  gl_FragColor = vColor;" +"}";private final int mProgram;private int positionHandle;private int colorHandle;//顶点数private final int vertexCount = triangleCoords.length / COORDS_PER_VERTEXT;//每个顶点占的字节数private final int vertexStride = COORDS_PER_VERTEXT * 4;public Triangle() {// 初始化顶点字节的缓冲区//需要在native 层分配内存ByteBuffer bb = ByteBuffer.allocateDirect(triangleCoords.length * 4);// 使用设备硬件的本机字节顺序bb.order(ByteOrder.nativeOrder());// 创建float缓冲区vertextBuffer = bb.asFloatBuffer();//将顶点坐标放进float缓冲区vertextBuffer.put(triangleCoords);// 设置缓冲区以读取第一个坐标vertextBuffer.position(0);int vertextShader = GlRender_1.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);int fragmentShader = GlRender_1.loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);// create empty OpenGL ES ProgrammProgram = GLES20.glCreateProgram();//将顶点着色器添加到项目GLES20.glAttachShader(mProgram, vertextShader);GLES20.glAttachShader(mProgram, fragmentShader);// creates OpenGL ES program executablesGLES20.glLinkProgram(mProgram);}public void draw() {// Add program to OpenGL ES environmentGLES20.glUseProgram(mProgram);// get handle to vertex shader's vPosition memberpositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");// Enable a handle to the triangle verticesGLES20.glEnableVertexAttribArray(positionHandle);// Prepare the triangle coordinate dataGLES20.glVertexAttribPointer(positionHandle,vertexCount,GLES20.GL_FLOAT,false,vertexStride,vertextBuffer);// get handle to fragment shader's vColor membercolorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");// Set color for drawing the triangleGLES20.glUniform4fv(colorHandle, 1, color, 0);// Draw the triangleGLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);// Disable vertex arrayGLES20.glDisableVertexAttribArray(positionHandle);}}

public class Square {//1.顶点坐标缓冲区private FloatBuffer vertextBuffer;//2.绘制顺序缓冲区private ShortBuffer drawListBuffer;//每个顶点包含坐标个数static final int COORDS_PER_VERTEXT = 3;static float squareCoords[] = {-0.5f, 0.5f, 0.0f,   // top left-0.5f, -0.5f, 0.0f,   // bottom left0.5f, -0.5f, 0.0f,   // bottom right0.5f, 0.5f, 0.0f}; // top rightstatic short drawOrder[] = {0, 1, 2, 0, 2, 3};private final int vertexCount = squareCoords.length / COORDS_PER_VERTEXT;private final int vertextStride = COORDS_PER_VERTEXT * 4;private final int mProgram;//绘制形状需要一个顶点着色程序和一个片段着色程序private final String vertexShaderCode ="attribute vec4 vPosition;" +"void main() {" +"  gl_Position = vPosition;" +"}";private final String fragmentShaderCode ="precision mediump float;" +"uniform vec4 vColor;" +"void main() {" +"  gl_FragColor = vColor;" +"}";// Set color with red, green, blue and alpha (opacity) valuesfloat color[] = {0.63671875f, 0.76953125f, 0.22265625f, 1.0f};private int positionHandle;private int colorHandle;public Square() {//1.在native 层分配内存 float 占4个字节ByteBuffer bb = ByteBuffer.allocateDirect(squareCoords.length * 4);//字节顺序bb.order(ByteOrder.nativeOrder());vertextBuffer = bb.asFloatBuffer();vertextBuffer.put(squareCoords);vertextBuffer.position(0);ByteBuffer dlb = ByteBuffer.allocateDirect(drawOrder.length * 2);dlb.order(ByteOrder.nativeOrder());drawListBuffer = dlb.asShortBuffer();drawListBuffer.put(drawOrder);drawListBuffer.position(0);int vertexShader = GlRender_1.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);int fragmentShader = GlRender_1.loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);mProgram = GLES20.glCreateProgram();GLES20.glAttachShader(mProgram, vertexShader);GLES20.glAttachShader(mProgram, fragmentShader);GLES20.glLinkProgram(mProgram);}public void draw() {GLES20.glUseProgram(mProgram);//顶点positionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");GLES20.glEnableVertexAttribArray(positionHandle);GLES20.glVertexAttribPointer(positionHandle, COORDS_PER_VERTEXT, GLES20.GL_FLOAT,false, vertextStride, vertextBuffer);//颜色colorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");GLES20.glUniform4fv(colorHandle, 1, color, 0);/**索引法绘制矩形*/Log.i("test", "draw: "+drawListBuffer.toString());Log.i("test", "draw: "+ Arrays.toString(drawOrder));GLES20.glDrawElements(GLES20.GL_TRIANGLES, drawOrder.length, GLES20.GL_UNSIGNED_SHORT, drawListBuffer);//Disable vertex arrayGLES20.glDisableVertexAttribArray(positionHandle);}}

说明:博客的所有内容均为自己探索实现的，受自身知识点的限制很多地方不一定正确的

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