Errors reported by IOS-based Xcode: Symbol not found

When using xcode for development, there may occasionally be errors that do not seem to be expected. What we encounter today is actually not an error. select commands + mouse on the keyboard.

-(UITableViewCell *) tableView :( UITableView *) tableView cellForRowAtIndexPath :( NSIndexPath *) The indexPath system function cannot be indexed. That is to say, the command left-click the keyword, the error "Symbol not found" was reported. in fact, this problem is well solved:

The main reason is thatIf the project index file is damaged, go~ /Library/Developer/Xcode/DerivedData
This folder can be used to delete all files related to the project. This folder does not affect the deletion of all files.

If your resource library is hidden, you can also use a relatively simple method.

Run the command line to open the folder to delete, or enter the DerivedData directory and run the rm command to delete the folder.