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 

b) assign .

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
     
       ().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
      
        ();		renderer.sharedMaterial = material;		return go;	}