The requireActivity() and requireContext() example

Introduced in Support Library 27.1.0

Photo by Clément H on Unsplash

This article is part of Today I Learned series and was originally posted at my TIL Github Repository and my website at wajahatkarim.com

When we use Fragment in our app, we often time need access to Context or Activity. We do it by calling methods such as getContext() and getActivity() methods. But, in kotlin, these methods return nullables and we end up using code like this.

fun myTempMethod()
    {
        context?.let {
            // Do something here regarding context
        }
        
        // Or we do it like this
        var myNonNullActivity = activity!!
    }

For example, we need Activity in asking permissions. So, with using above code approach, this will be:

fun askCameraPermission()
    {
        PermissionUtils.requireCameraPermission(activity!!, REQUEST_CODE_CAMERA)
    }

Now, this code is very bad. When Fragment is not attached to any Activity, this code will crash and throw NullPointerException. Some developers avoid this by using as operator.

fun askCameraPermission()
    {
        PermissionUtils.requireCameraPermission(activity as Activity, REQUEST_CODE_CAMERA)
    }

But, this is also almost same as bad as the previous example. Luckily, in Support Library 27.1.0 and later, Google has introduced new methods requireContext() and requireActivity() methods. So, we can do above example like this now:

fun askCameraPermission()
    {
        PermissionUtils.requireCameraPermission(requireActivity(), REQUEST_CODE_CAMERA)
    }

Now, this method will make sure that Fragment is attached and returns a valid non-null Activity which we can use without any trouble.

EDIT: Thanks to

Ahmed Ashraf Gamal

for pointing out that if the Fragment is not attached to the Activity , then the requireActivity() or requireContext() methods will throw IllegalStateException .

Credits: https://twitter.com/renaud_mathieu/status/1019222211004129282

Wajahat Karim is a graduate from NUST, Islamabad, an experienced mobile developer, an active open source contributor, and co-author of two books Learning Android Intents and Mastering Android Game Development with Unity. In his spare time, he likes to spend time with his family, do experiments on coding, loves to write about lots of things (mostly on blog and medium) and is passionate contributor to open source. In June 2018, one of his library became #1 on Github Trending. His libraries have about 2000 stars on Github and are being used in various apps by the developers all around the globe. Follow him on Twitter and Medium to get more updates about his work in Writing, Android and Open Source.

Wajahat Karim (@WajahatKarim) | Twitter

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