Validating permissions on Android with Kotlin

October 07, 2019  2 minute read  

I’m continuing my educational coding exercise, developing a new photo sharing app. Recently, I completed my user authentication and registration process and I’m now quite happy with it, so I moved on to taking photographs. I’ve got an activity with a toolbar and a floating action button:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/main_container"
    tools:context=".activities.MainActivity">

    <include
        layout="@layout/main_toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/main_fab_camera"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="32dp"
        android:layout_marginBottom="32dp"
        android:clickable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:srcCompat="@drawable/ic_camera_white_48dp" />

</androidx.constraintlayout.widget.ConstraintLayout>

In the MainActivity, I’ve set up an onClickListener as follows:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(findViewById(R.id.toolbar))

        main_fab_camera.setOnClickListener { validatePermissions() }
    }

The question before me is this: How do I ask for permissions on Android?

The hard way

Naturally, Android has its own system of doing things. It boils down to this:

  1. Declare the permissions you want in your AndroidManifest.xml file.
  2. Use ContextCompat.checkSelfPermission() to see if you have the permission.
  3. If you don’t have the permission, show the rationale, and request permissions.
  4. Define a callback to receive the result of the request permissions.

It’s actually a lot of boiler plate code, which I won’t show here because the android.developer.com has already done it.

The easy way

This left me searching for an alternate way, and I found it in a small library called Dexter - contributed to open source (Apache 2.0 licensed) by Karumi. Basically, it simplifies the way you ask for permissions.

In my case, I need to ask for multiple permissions, so let’s go through the process. First, we declare the permissions in the AndroidManifest.xml file:

    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Next, add the library to the app-level build.gradle:

dependencies {
    // Other dependencies here
    implementation "com.karumi:dexter:6.0.0"
}

Don’t forget to sync.

Finally, call Dexter in your app to check for licenses:

private fun validatePermissions() {
  Dexter
    .withActivity(this)
    .withPermissions(
      Manifest.permission.CAMERA,
      Manifest.permission.READ_EXTERNAL_STORAGE,
      Manifest.permission.WRITE_EXTERNAL_STORAGE
    )
    .withListener(object : MultiplePermissionsListener {
      override fun onPermissionsChecked(report: MultiplePermissionsReport?) {
        launchCamera()
      }

      override fun onPermissionRationaleShouldBeShown(permissions: MutableList<PermissionRequest>?, token: PermissionToken?) {
        Timber.d("Skipping rationale request in validatePermissions()!")
      }
    })
    .check()
}

We declare the list of permissions we want in the .withPermissions() and then add a callback that is called when it wants something. In this case, once I’ve got all the permissions approved, I call launchCamera(). If the permissions failed, then it drops through and returns - nothing actually happens.

There is another version of this that provides an onFailure callback for checking an individual permission. This allows you, for example, to disable the camera button when you get a declined to prevent the user from clicking the button in the future.

You can see the code for this in my GitHub repository.

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