OpenGL ES2 Vertex Array Objects help - ios

Question

I am having trouble understanding how to use VAO's in OpenGL ES2 (on iOS) and getting them to work.
My current rendering setup looks like this (in pseudocode):
Initialization:
foreach VBO:
glGenBuffers();
Rendering a frame:
// Render VBO 1
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO1);
foreach vertex attribute:
glVertexAttribPointer();
glEnableVertexAttribArray();
glBufferData(GL_ARRAY_BUFFER, ...);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ...);
glDrawElements(GL_TRIANGLE_STRIP, ...);
// Render VBO 2
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO2);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO2);
foreach vertex attribute:
glVertexAttribPointer();
glEnableVertexAttribArray();
glBufferData(GL_ARRAY_BUFFER, ...);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ...);
glDrawElements(GL_TRIANGLE_STRIP, ...);
This works fine, however, both VBO's have exactly the same interleaved vertex attribute struct, and as you can see I'm setting up and enabling each attribute every frame for every VBO. Instruments complains about redundant calls to glVertexAttribPointer() and glEnableVertexAttribArray(), but when I move one of them or both to the initialization phase I either get a EXC_BAD_ACCESS when calling glDrawElements or nothing is drawn.
My question is whether I need to do this every frame, why it doesn't work if I don't, and how I would use VAO's to solve this.

Answer 1

Sorry for the dredge, but I'm procrastinating and you keep topping my google search. I'm sure you've solved it by now...
The correct way is to only update the buffers when the data changes, not every frame. Ideally, you would only update the part of the buffer that changed. Also, Attribute Pointers are offsets into the buffer if a buffer is bound.
Initialisation:
glGenBuffers()
foreach VBO:
glBufferData()
Updates / Animation, etc:
glMapBuffer() //or something like this
buffer->vertex = vec3(1,2,3) // etc
glUnmapBuffer()
And Render:
glBindFBO()
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO1)
glVertexAttribPointer(GL_VERTEX,..., 0) // Buffer Offset = 0
glVertexAttribPointer(GL_TEXCOORD,..., sizeof(vertex)) // Buffer Offset = size of vertex
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO1);
glEnableVertexAttribArray(..., 0) // Buffer Offset = 0
glBindBuffer(0); // Unbind buffers, you don't need them here
glDrawElements(GL_TRIANGLE_STRIP, ...);
Hope that helps.