Uploading json assets and icons to your app via the app generator

If you have tried out our app generator webpage, you should’ve noticed an option that allows you to upload a zip file which will contain the json for the event.

Why do we need this?

Well, this is needed because not every event organizer can maintain a server and API endpoints which contain the details for their event, so they can simply generate a json for the event by exporting it through the options provided to them on Google Spreadsheets and then they can upload them on the server, so that these files can be packaged in the android and web apps.

Implementation :

The implementation is pretty straightforward and consists of 3 parts :

  1. Making changes to the html file to allow user to upload the zip
  <td valign="top">
    <label for="sessions">Zip containing .json files</label>
  <td valign="top">
    <input accept=".zip" type="file" id="uploadZip" name="sessions">

2. Retrieve this file in the javascript and then make an AJAX call to the server

var file_data = $('#uploadZip').prop('files')[0];
 var form_data = new FormData();                 
 form_data.append('file', file_data);
                  url: '/upload.php', // point to server-side PHP script
                  cache: false,
                  contentType: false,
                  processData: false,
                  data: form_data,                         
                  type: 'post',
                  success: function(php_script_response){
                    // do something

So here, the form_data contains the details about the file to be uploaded.

In the AJAX call, upload.php takes reads form_data variable and then initiates the upload to the server.

3. Setup a PHP script on the server to respond to the above AJAX call

    if ( 0 < $_FILES['file']['error'] ) {
        echo 'Error: ' . $_FILES['file']['error'] . '<br>';
    else {
        move_uploaded_file($_FILES['file']['tmp_name'], "/var/www/html/uploads/upload.zip"); 

Here in the PHP script, the file is read and uploaded to a temporary directory in the server.

We then manually copy it to a location and name of our choice.

In case there are multiple users accessing the website and uploading their assets at the same time, we need to pass a timestamp variable to the AJAX call to and later on use it while renaming the uploaded file.

This is to ensure that the file uploaded by one user is not overwritten by another user.

How do we use this data during app compilation

The uploaded zip is then uncompressed and its contents are moved to the assets folder of the android app’s directory.

zip_ref = zipfile.ZipFile(path_to_zip_file, 'r')
#TODO: Change path here
for f in os.listdir(directory+ "/zip"):
	if f.endswith('.json'):
		copyfile(f, directoy + "open-event-android/android/app/src/main/assets/"+f)
	elif f.endswith('.png'):
		copyfile(f, directory + "open-event-android/android/app/src/main/res/drawable"+f)
replace(directory+"/open-event-android/android/app/src/main/res/values/strings.xml", 'mipmap/ic_launcher', 'drawable/' + f)

Here replace is a function that searches in the source file for the phrase supplied as it’s argument and changes it with the new phrase.

Now when the app is compiled and ran on a user’s device, it will first search for a json file in the assets directory and if it exists, use that for fetching the data instead of making a network call. For this I have used Gson to first parse the offline files otherwise retrofit makes request to the api and fetches the data from there.

But if there is no json in the assets folder, a normal network call using retrofit will be made and the data will be fetched from the API defined by the user.