Extension Functions + AndroidManifest's Tag

2020, Apr 19    

If you are building an Android library, then you might need to read <meta-data> tag of your user. I came across with similar situation, where I need to do the same.

My initial code looked something like this:

fun getVersion(): Int {
    val appInfo = packageManager.getApplicationInfo(packageName, PackageManager.GET_META_DATA)
    val metaData = appInfo.metaData
    return metaData.getInt(META_KEY_VERSION)

However, this didn’t scale well. As my library grew, I wanted to give more control to library users and hence more <meta-data> tags were being introduced. And to read them, I have to write more methods like getVersion() scattered in many Activity classes.

So I have refactored it to create few extension functions like this:

fun AppCompatActivity.getMetaData(): Bundle =
    packageManager.getApplicationInfo(packageName, PackageManager.GET_META_DATA).metaData

Now, I can simple call getMetaData().getString(...) or getMetaData().getInt(...), etc. And to make it even more intuitive, we can also create few more extensions like this:

fun AppCompatActivity.getMetaString(key: String) = getMetaData().getString(key)

fun AppCompatActivity.getMetaInt(key: String) = getMetaData().getInt(key)

Now, we can simply call getMetaString(...) from any Activity to get the <meta-data> declared by user.