Xcode's duplicate symbol xx problem

Today in the writing process encountered a wonderful problem.

The first n tables, my app can compile and run. After a second suddenly can not compile through, through the reading the wrong information, found that is duplicate symbol xx problem, the problem appears in the connection.

Why??

The first literal meaning is repeating the definition. ( But why the previous can be compiled by not error?) Steve Jobs, you live for me, I promise not to kill you! )

In fact, the solution is very simple, the full text to find this XX. You will find that the variable is defined in several files that connect to the error prompt. ( my local variable (written in. m, is this a local variable?) I am a rookie, at least the instance can not access the connection error?? ). Then all you have to do is get rid of one of the names.

Solve the problem, forget, the figure is subsidized.

Off Topic:

1. You should pay attention to the names of different classes and avoid the same names. Just in case, the variables in different classes are prefixed with the class name ....

2: How do you not error, not the same kind of for the loop I repeat definition of it??

Xcode's duplicate symbol xx problem