duplicate symbol _main in:
/Users/mb467/Library/Developer/Xcode/DerivedData/barChartDemo-gevlnavnpanltbgqdweijouguhcx/Build/Intermediates/barChartDemo.build/Debug-iphoneos/barChartDemo.build/Objects-normal/armv7/main-CCADE8545E02147B.o
/Users/mb467/Library/Developer/Xcode/DerivedData/barChartDemo-gevlnavnpanltbgqdweijouguhcx/Build/Intermediates/barChartDemo.build/Debug-iphoneos/barChartDemo.build/Objects-normal/armv7/main-3D90E6383DC1F398.o
ld: 1 duplicate symbol for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)
问题：main.m 文件重复了，删除其中一个即可