MapApp2 : App Design

Welcome to the third part of my tutorial on how to create a map app for Android without using Google™ APIs :).

Series outline:

• Series aim.
• Theory you need to know.
• App design.
• Writing a TilesManager.
• Writing a TilesProvider.
• Seeing results with MapView.
• Adding web support.
• Creating MapView in XML.
• Extra: Fuchs Maps.

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Okay, I’m supposed to show you a class diagram here but I changed my mind, since the app is simple I’ll explain each class in some lines :).

TilesManager: this class contains all the calculations needed to power our app, as I mentioned before maps are made up of tiles, we need to know exactly what tiles to fetch, we also need to convert latitude and longitude to pixel coordinates to display markers, this class by itself doesn’t contain the tiles, it just provides us with methods to know what tiles are visible and where to render them.

This class can be extremely easy to be written in JAVA without any Android libraries (I’m just using Android’s Rect and Point classes).

TilesProvider: receives a range of tiles indices (indexes ;)) then fetches the required tiles images, in our case the tiles are fetched from a database, to make an online map application you just need to change some functions in this class.

If you want your app to support both online and offline modes, extract an interface from this class and use it as your tile source, I think I’ll explain how to get tiles from OpenStreetMap later.

Fetching tiles from the database is time expensive, so we will add simple caching to this class , this also helps a lot when dealing with online map servers, caching in this case will save you both time and bandwidth, you’ll also save the tile servers some trouble :D.

MapView: a custom View that will ask a TilesManager (using location data) about what tiles we should render and where, then it asks a TilesProvider for the images of those tiles and finally renders them.

MapView will respond to touch events to enable panning.

Tile: each tile simply contains x,y index and a Bitmap (The actual image of the tile), no z or zoom index since we render one zoom level at a time.

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Other classes exist and will be discussed when they are needed :).

In the next part of the tutorial we will start the actual coding :).