android中xml文件的解析是在运行时还是编译时发生的？

I am far from an expert when it comes to understanding the minutia of code compilation. But I am learning some android development, and I noticed how layouts and other things are essentially parsed out of xml. I was wondering if this parsing happens at compile time or at runtime? If it is at runtime, it seems like there might be some overhead associated with parsing out a very complex layout. I am far from an expert when it comes to unders