摘要：
https://msdn.microsoft.com/en-us/library/ebca9ah3.aspx The override modifier is required to extend or modify the abstract or virtual implementation of 阅读全文
摘要：
https://msdn.microsoft.com/en-us/library/9fkccyh4.aspx The virtual keyword is used to modify a method, property, indexer, or event declaration and all 阅读全文