1.只能重新生成新的mesh，重新赋值
2.生成的mesh，必须按照官网文档，同时指定：顶点与三角形的index数组，否则不行的
a) assign vertices
b) assign triangles.
3.例子：用代码生成mesh为指定size的cube：
GameObject createCube (Vector3 meshBoundSize)
{
GameObject go = GameObject.CreatePrimitive (PrimitiveType.Cube);
Mesh mesh = new Mesh ();
float x = meshBoundSize.x / 2;
float y = meshBoundSize.y / 2;
float z = meshBoundSize.z / 2;
mesh.vertices = new Vector3[] {
new Vector3 (-x, -y, -z),
new Vector3 (x, -y, -z),
new Vector3 (x, y, -z),
new Vector3 (-x, y, -z),
new Vector3 (-x, y, z),
new Vector3 (x, y, z),
new Vector3 (x, -y, z),
new Vector3 (-x, -y, z),
};
//anticlockwise
mesh.triangles = new int[] {
3, 1, 0,
3, 2, 1,
2, 3, 4,
2, 4, 5,
7, 5, 4,
7, 6, 5,
0, 6, 7,
0, 1, 6,
3, 7, 4,
3, 0, 7,
1, 5, 6,
1, 2, 5
};
mesh.RecalculateNormals ();
mesh.RecalculateBounds ();
go.GetComponent<MeshFilter> ().mesh = mesh;
Material material = new Material (Shader.Find ("Transparent/Diffuse"));
Color color = Color.red;
color.a = 0.2f;
material.SetColor ("_Color", color);
MeshRenderer renderer = go.GetComponent<MeshRenderer> ();
renderer.sharedMaterial = material;
return go;
}