BMI app

Introduction

This app was created for the Mobile Applications course. Main features that were required to implement:

• app should allow to select the units (input fields should be cleared after such change),
• color of the BMI score should be changing accordingly to the category that this result belongs to (and should be inaffected by the screen rotation),
• app should have a history of the last 10 calculated BMIs with their date, weight and height values and the score,
• calculated score should have a corresponding description of the BMI category,
• app should have a page about the author.

Demo

Here are some screenshots presenting the basic usage of the app.

Implementation details

This application uses the MVVM architectural pattern.

MainActivity has a reference to the MainViewModel which is responsible for:

• communicating with the UnitAdapter to retrieve the currently selected units,
• updating height and weight values (and BMI score if needed),
• communicating with the BMIcalculator to get the properly calculated BMI score after passing height and weight values and proper scaling factors for the selected units retrieved from the UnitAdapter
• communicating with the HistoryHandler in order to add new entries to the history.

MainActivity:

• implements the Observator design pattern to observe the bmi_value() function (from the MainViewModel) which returns a LiveData<Double?>.
• offers the user a menu to start new activities,
• controlls the UI components in order to properly react for the changes by notifying MainViewModel.

UnitAdapter:

• stores two maps with keys being the names of the height and weight units and values being the scaling factors of those units to the SI units (m and kg),
• uses SharedPreferences to store selected units by the user,
• provides an easy access to the unit and its scaling factor for the other classes.

BMIcalculator - implements a formula to calculate the BMI score. It is a separate object hence it is easy to find that formula and adjust it if needed.

HistoryHandler:

• uses SharedPreferences to permanently store the list of 10 last entries as a StringSet (entries are serialized to the JSON format first and then added to the set),
• provides a loadSortedHistoryList() function that loads stored set, changes it into a mutableListOf<HistoryEntry> by deserializing each entry and sorts the list in a descending chronological order,
• provides an addEntry() function that takes care about adding new entries while not exceeding the size limit of the list.

DescriptionProvider - this object is responsible for providing data about each BMI category. It has four maps - each of them maps the category ID to respectively: category name, category upper bound, category color and category description. It has a function that returns a category ID based on the BMI score passed as an argument. Then this function is used to get the other properties related to the category based only on the BMI score.

History activity uses a RecyclerView with a custom RecyclerAdapter to display previously calculated entries.

Settings displays the spinners to let the user select the unit. After such a selection it notifies the UnitAdapter about the change.