Define a one to many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
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转载于:https://www.cnblogs.com/xuxiaoguang/archive/2007/08/01/839190.html
Define a one to many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
转载于:https://www.cnblogs.com/xuxiaoguang/archive/2007/08/01/839190.html