How I created a custom geo-query function to find posts under a specified range from the current location.

fodome - This is an android app that connects food donors with the needy. The app has food posts and each post has its location detail captured while uploading. Once the user is authenticated and inside the home feed page, initially, all the posts are shown since the location access is not enabled. After enabling the location, the user is prompted to confirm the current location. The posts are now filtered by location and by default the range is set to 20kms. The user can customise the range from 1km to 1000kms. For accessibility, few frequently used ranges are displayed as chip filters - 10km, 20km and 50km. A custom range chip button is displayed which on tap will pop up the hidden custom range bar which can be used to set range from 1-1000kms. Once the range is updated, all the posts are refreshed and only those posts are displayed which fall under the specified range. Each post has a location detail with its latitude and longitude. We also have the user’s current location latitude and longitude. If the range is set as 20kms then a custom function will go through each post and find the distance between the user’s current location and the post location. If the distance falls under the specified range then the post is displayed. This will continue for all the posts uploaded to the app. If the range is updated, the custom function will run again and fetch the posts which fall under the new range. The time complexity of this function is O(n) where n is the number of posts. We can also reduce the number of posts computed if the posts grow to a large number and only compare the first 50-100 posts and compute the next few posts only when the user scrolls over the pre-computed posts. This will definitely improve the time complexity when the number of posts grows to more than a million.

Download the app or check the source code on github.