To run the app, download the code. Then, sign up on openweathermap and issue a free API KEY. Now store this API KEY in QueryUtils.java as a String variable called API_KEY.

This is a basic app to show weather information of the current location of the Android device. This app is great for beginners to understand. The app :-

1. has Minimal UI.
2. fetches data from OpenWeatherMap API.
3. accesses Phone Location by using the permissions in Android.
4. is designed in using a scalable approach

This README also contains the approach that was followed while developing this app so that beginners can relate to it.

I first began by thinking about the UI for the app. Since the app has to show only the weather information of the current location of the device, I decided that app should have only one screen in which the information would be displayed. I chose the RelativeLayout ViewGroup because it is easier to align views using this view group. Inside the group, there would be two textViews - one for displaying temperature and other for displaying the city. I inserted dummy data while I was working on the UI. The UI finally looks like the following:-

Now that the UI is created, it is time for our app to fetch data from an API. On google, I found a weather API called openweathermap. On its website, I registered myself for the free tier and generated an API key. This key must be sent as a parameter in the request URL. Next, I saw their documentation to know the format of the request URL. It had the following format

https://api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}

Now, I created a new class called QueryUtils which contained all the methods for making an HTTP request and parsing the JSON response obtained. The QueryClass had the methods to perform the following functions:-

1. Create an URL object (For now, I hardcoded the city name).
2. Establishing connection to API and obtain the response
3. Parse the response (obtained from API) to String. (The response of the API is in binary, hence we must convert it to ASCII characters.)
4. Fetch the relevant details i.e. City and Temperature from the String (obtained from Step 3) (The string contains the data in JSON format).

Also, remember to add Internet Permission in AndroidManifest.xml.

If I try to run the app, it crashes as soon as it starts. On checking the logs in Android Studio, I found out that the app crashed because an NetworkOnMainThread Exception was thrown as soon as the app starts.

On Searching about this error on the internet, I realised that Android Platform does not allow network calls on Main Thread to ensure a smooth UI Experience for the user.

On further searching on the internet, I found that we can use the class AsyncTask to execute network calls on a background thread. It is an abstract class.

After implementing the class, the app runs smoothly. One problem is that the API sends temperature in Kelvin.

So now I wanted to convert temperature from kelvin scale to celsius scale. It is simple. We can simply create a method to achieve this. But the important question to ask is where to implement this method. I can implement this method in QueryUtils class or in MainActivity class. The better location is to implement this method in MainActivity because in future, if someone wants to display the information in Fahrenheit, one would have to change code in MainActivity only.

Advanced Information

Suppose the app were displaying weather info of my cities in a list format. And, If I were using ListView with ArrayAdapter, I would have called the kelvinToCelsius method in getView function of adapter class because we need to convert only those temperatures which are currently visible to the user. This would be more efficient for the hardware.

Now it is time to add location detection feature to this app. I googled 'Current Location Android Developers'. I first opened Android Developer docs by Google and then I found one article on geeksforgeeks. With the help of these two articles, I addded the code to fetch the current location of the android device.