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androidapi

Saving the API Key in gradle.properties

I am new to android and working on a project where I see that the API key that I got is saved in gradle.properties as :

MyOpenWeatherMapApiKey="1c3ae96f93a0094e8a7chsjdgfid04aed3f10"

And then in build.gradle(module:app) I am adding the following lines : 

buildTypes.each {
            it.buildConfigField 'String', 'OPEN_WEATHER_MAP_API_KEY', MyOpenWeatherMapApiKey
      }

So, in my main program I am accessing the data using this api whose URL is got by this piece of code :

final String FORECAST_BASE_URL = "http://api.openweathermap.org/data/2.5/forecast/daily?";
            final String QUERY_PARAM = "q";
            final String FORMAT_PARAM = "mode";
            final String UNITS_PARAM = "units";
            final String DAYS_PARAM = "cnt";
            final String APPID_PARAM = "APPID";
            Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
                    .appendQueryParameter(QUERY_PARAM, params[0])
                    .appendQueryParameter(FORMAT_PARAM, format)
                    .appendQueryParameter(UNITS_PARAM, units)
                    .appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
                    .appendQueryParameter(APPID_PARAM, BuildConfig.OPEN_WEATHER_MAP_API_KEY)
                    .build();
            URL url = new URL(builtUri.toString());

So, my question is that why taking all the tension of doing changes to store the appid in the gradle part. Can't we access directly in the main program only ?

And the second part of my question is what is actually happening in the gradle part especially with the buildTypes.each{} block ?

Solution
    1. The idea of this indirection is to allow you to store API key in files that are not uploaded to the version control: gradle.properties is a local file and should not be stored under the version control, and BuildConfig is a generated class, so it will only be created at build time. It's definitely easier to store the API key somewhere as a plain String, but then you'll have to commit it to the repo.
    2. During build time, Gradle will generate the BuildConfig file to store some build-related constants. You can use buildConfigField command to instruct Gradle to add custom fields into BuildConfig. After the project is built, you can reference these constants inside your source code.