Simple Calculator

Simple calculator is a simple calculator with only addition and subsctraction, using decimals as well. This project uses Clean architecture by means of Model-View-Presenter (MVP) as well as Dagger 2 for Dependency Injection, trying to respect SOLID principles as much as possible.

Logo

Screenshots

Overview

At this open-source project, it is decoupled between android and domain modules or high level layers.

This means, android is strongly coupled with the Android framework and domain is decoupled from it, and can be re-used for other purposes when required as is purely Java based, but not framework coupled.

Architecture design overview

The exchange between the different layers is as follows:

Interactor layer: from the Interactor, which is responsible of the business logic and communicating results to the Presenter
Presenter layer: from the Presenter, which orchestrates different interactors when required and also provides the final formatted info to a passive View from a UI element (fragments / activities). Finally, this information would be passed through the UI thread.

Material design

This code test uses a wide range of Material design widgets from the Design support library such as:
AppBarLayout, CoordinatorLayout, Toolbar, as well as Material theme styles.

Features

When the app opens a calculator interface is displayed to the user.
The calculator should have buttons for:
- Numbers 0 to 9
- Decimal point
- Addition
- Subtraction
- Equals (to see the result)
As the buttons are pressed, they are entered into the output view at the top.
Once, the user presses the “=” key, then the result is computed and displayed in the output field.
- For example: For input: 1 2 + 6 5 - 7 Then, the output view would now display: 12+65-7
- When “=” is pressed, the output view would now display: 70
- After the result has been calculated if either “+” or ”-” is selected, then this operation will be applied to the result currently displayed in the output view.
- For example: The output view currently displays: 70
- For input: + 1 6 - 2 Then, the output view would now display: 70+16-2
- When “=” is pressed, the output view would now display: 84
A Loader is placed each time a read of operations or calculation is started, to indicate the user the fact that there is an action going on (when too quick is not visible)
There are Unit test cases for the most critical parts:
- The strategy for calculating after and parsing inputs from the screen (domain)
- Characters validation for combinations like:
- user press + & + then only one + is on screen
- user press + & - then only one - is on screen
- user press - & - then only one + is on screen
- user press . with a + before, then 0. is on screen
- Strings transformation tests for checking correctness
Includes a < which is responsible of cleaning the screen when something is wrong or starting a new operation

SDK support

Support SDKs from 16 to 25

Disclosure - Libraries used

Dagger 2 for Dependency Injection
ButterKnife v6.1.0 for Views Injection
Mockito for Mocking artifacts
JUnit for Unit tests

References (special thanks) - those are the same I indicated at my personal blog (Insights and projects):

Uncle Bob: The Clean Architecture by Uncle Bob
The Repository pattern by Microsoft
Effective Android UI by Pedro Gomez
Android Clean Architecture by Fernando Cejas

Contributions

Please read first CONTRIBUTING

About the author

Raul Hernandez Lopez,

License

Copyright (C) 2017 Raul Hernandez Lopez

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

raulh82vlc/SimpleCalculator