cocoa: nsarraycontroller add object error
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In my MainController, there's a persons array, which binds to a NSArrayController. The persons's name are displayed in a table `name` column. If I bind a button to NSArrayController add method, I can add the button to add a new person, but if add the new person in method, the the tabel doesn't show the new person, I don't know why.

![enter image description here][1] 


  [1]: http://i.stack.imgur.com/W0f9Z.png

my code to add new person

    Person *p =[[Person alloc]init];
    [self.persons addObject:p];