Module 12: Creating an Uber Clone
Transcript
we can now move forward to the last two pieces of the search service class if the last request is this request which can happen as a user types and deletes etc then we don’t want to do anything let the last request finish however if it isn’t then we want to kill the last request which might still be queued and blocking us from going forward we check if an entry is already in the cache as users might type and revise a lot thus triggering significant web service cost overhead we clean the variable values and then invoke the response notice i use call serially in this case to defer the response to the next cycle if we call back immediately we might delay the input code which is currently in place by shifting the callback to the next edt cycle we guarantee that suggest locations will behave in a similar way whether the data is cached locally or not the request extracts the predictions array so we can construct the result list we iterate over the entries notice i discard the generic context which is legal in java but might produce a warning i could have used a more elaborate syntax that would have removed the warning but that would have created more verbus code with no actual benefit i extract the elements from the map and create the suggestion result entries then store the whole thing in cash followed by the on success call notice that this in this case i didn’t need the call serially since the response is already asynchronous the final web service api we will cover is the directions api which will allow us to set the path taken by the car on the map the directions api is challenging it returns encoded data in a problematic format this is the sample query from google notice we can give the origin and destination values as longitude latitude pair which is what we’ll actually do the response is a bit large so i trimmed a lot of it to give you a sense of what we are looking for the one thing that matters to us from the response is the overview polyline entry which seems like a bunch of gibberish but it isn’t this is a special notation from google that encodes the latitude longitude values of the entire trip in a single string this encoding is described by google in their map documentation being lazy i found someone who already implemented the algorithm in java and his code worked as is i won’t go into the code since it’s mostly just bitwise shifting to satisfy requirements from google the method signature is the only thing that matters it takes an encoded string and returns the path matching that string as a list of coordinates that we will be able to add into the map shortly now that this is all out of the way the directions method is relatively simple this method is just another rest call that doesn’t include anything out of the ordinary we extract the overview polyline value and pass it to the callback response