Here are a list if Xcode trouble shooting scenarios and what they usually mean.

Missing dependency target – file not found

Screen Shot 2017-03-22 at 8.21.55 AM.png

This usually means your subproject is foobar and you need to re-add it.

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Go here and follow the instruction on how to do that.

Undefined symbols for architecture

Screen Shot 2017-06-29 at 2.33.08 PM.png

Check the target membership of the file in question. Maybe you got it wrong.

For example here I had this

Screen Shot 2017-06-29 at 2.40.59 PM.png

When really it should have been this

Screen Shot 2017-06-29 at 2.41.08 PM.png