带有自定义键的NSDictionary的行为奇怪--偶尔将值更改为null和back。

Question

我在NSMutableDictionary上遇到了问题，我正在通过一个循环来填充这个问题，这个循环使用的是键的自定义对象类型。我已经实现了NSCopying，所以我希望一切都会好起来。看着循环的结果，我注意到键看起来很好，但是值在NULL中来回翻转是很奇怪的。每次迭代时字典的控制台输出：

{
    "C#-10" = "<SWPP_BeamModel: 0xc4ba470>";
    "D-10" = "<SWPP_BeamModel: 0xc4b5600>";
    "C-10" = "<SWPP_BeamModel: 0x1277f810>";
}
// ...ok so far

{
    "C#-10" = "<SWPP_BeamModel: 0xc4ba470>";
    "C-10" = "<SWPP_BeamModel: 0x1277f810>";
    "D#-10" = (null);
    "D-10" = "<SWPP_BeamModel: 0xc4b5600>";
}
// ...oops a null

{
    "C#-10" = "<SWPP_BeamModel: 0xc4ba470>";
    "C-10" = "<SWPP_BeamModel: 0x1277f810>";
    "D#-10" = (null);
    "D-10" = "<SWPP_BeamModel: 0xc4b5600>";
    "E-10" = (null);
}
// ...and another

{
    "C#-10" = "<SWPP_BeamModel: 0xc4ba470>";
    "C-10" = "<SWPP_BeamModel: 0x1277f810>";
    "D#-10" = (null);
    "F-10" = (null);
    "D-10" = "<SWPP_BeamModel: 0xc4b5600>";
    "E-10" = "<SWPP_BeamModel: 0x1277fad0>";
}
// ...another but value for key "E-10" is back!

它就这样继续下去。最后的结论是这条线..。

// De-mutablise
_noteBeamsMap = [NSDictionary dictionaryWithDictionary:beamsMap];

，从而导致_noteBeamsMap为

{
    "D#9" = (null);
    G1 = (null);
    C14 = (null);
    "G-7" = (null);
    ...

怎么回事？

Answer 1

结果是，我在自定义key类中实现了isEqual:，但没有实现匹配的hash。简单地说，在这篇有用的博客文章中 hash需要在isEqual:返回YES时返回相同的值。