Module 12: Creating an Uber Clone
Transcript
we finally have a client server application that works but we don’t have any real functionality to get to that point we need some web services WebServices from the Device? i chose to invoke the google web services from the device code instead of using our server to proxy the calls i did this because this is a mobile programming course not a server development course this makes sense for a simple project and is arguably faster as i connect directly to google however if i was building a real world application i would have directed all requests to our server and invoked google from there this might have a performance penalty but it’s worth it here are some of the advantages api keys would be stored on the server and would thus be more secure from theft we can cache queries and reduce api costs between users currently i can only cache calls per user but if lots of people are searching for the same things this can add up i can use analytics and statistics in the server code and notice patterns about user behavior and finally i can switch to a different company for the web service implementation to get a better deal if google discontinues its service i don’t have to ship an app update either Googles GIS Services we’ll use four google location-based web services to implement the functionality of this app with geocoding we provide an address or location and get back a location on the map this is useful when a driver receives a set of locations and need to know the actual map coordinates reverse geocoding is the exact opposite it provides the name of a given location this is useful for pointing a pin on the map and naming the location directions provides directions trip time etc we can get the points of the path and plot them out on the map the places api allows searching for a place similar to the geocoding api the auto complete version lets us type into a text field and see suggestions appear we’ll use it for the search functionality New Fields in Globals all of these apis require developer keys which you can obtain from their respective websites i’ve edited the globals class to include these new keys required by the three apis make sure to replace the dashes with the relevant keys you can get the keys by going to the directions geocoding and places websites and follow the process there we use the maps api geocode json url for reverse geocoding google provides this example for usage of the api it’s just a latitude longitude pair and your api key Reverse Geocoding - Result the result of that url look like this response json let’s go over two important pieces we need to get this result array from the response we only care about the first element and will discard the rest this is the only attribute we need at this time from this api now that we know what we are looking for let’s look at the code that accomplishes this SearchService i’ll use the search service class to encapsulate this functionality for each of these services there is an edge case where location isn’t ready yet when this method is invoked in this case i found it best to just do nothing usually it’s best to fail by throwing an exception but that is a valid situation to which i have a decent fallback option so i prefer doing nothing if we send two such calls in rapid succession i only need the last one so i’m canceling the previous request the reverse geocode api latitude long argument determines the location for which we are looking we get the past result as a map containing a hierarchy of objects the callback is invoked asynchronously when the response arrives this gets the result list from the json and extracts the first element from there we extract the one attribute we care about the formatted address entry and invoke the callback method with this result the places autocomplete api is a bit more challenging since this api is invoked as a user types we’ll need the ability to cancel a request just as we would with the geocoding calls caching is also crucial in this case so we must cache as much as possible to avoid overuse of the api and performance issues let’s start by reviewing the api url and responses the default sample from google wasn’t very helpful so i had to read the docs a bit and came up with this url the search is relevant to a specific location and radius otherwise it would suggest places from all over the world which probably doesn’t make sense for an uber style application notice the radius is specified in meters the input value is a the string for which we would like autocomplete suggestions Places Autocomplete - Result this request produces this json result all predictions are again within an array but this time we’ll need all of them the ui would require the text broken down so we need the main text and we’ll need the secondary text to we’ll also need the place id and the reason for this is a huge omission in this api notice it has no location information we will need the place id value to query again for the location SuggestionResult before we move on to the code will need a way to send the results back we can do that with a list of suggestion result entries this is a pretty trivial class and doesn’t require any explaining the class solves the issue of getting the location for a specific entry with the method get location i won’t go too much into the details of that code above since it’s very similar to the code we saw before we just get additional details about a place and parse the results notice that this is a part of the suggestion result class so we don’t invoke this unless we actually need the location of a place there is one last thing we need before we go into the suggestion method itself we need variables to cache the data and current request otherwise multiple incoming requests might collide and block the network we need the last suggestion request so we can cancel it the last suggestion value lets us distinguish duplicate values this can sometimes happen as an edit event might repeat a request that was already sent for example if a user types and deletes a character this can happen since we will wait two 500 milliseconds before sending characters the location cache reduces duplicate requests notice that this can grow to a level of a huge memory leak but realistically that would require a huge number of searches if this still bothers you we can have the cash map class that serializes extra data to storage