Android Full Screen Activity to View Zoomable Image

The following library are used

PhotoView - Zoomable ImageView
Glide - Image loading library

The activity shall have the following features

Full screen: no status bar
Action toolbar shall overlay the image: maintain back icon to close the activity
Click the on image will toggle dark mode (background change to dark color and hide toolbar)
Image shown shall be zoomable

Enable Fullscreen Mode

Edit AndroidManifest.xml

<manifest ...>
    <application ...>
        <activity
            android:name=".view.support.ImageViewActivity"
            android:label="@string/title_activity_image_view"
            android:parentActivityName=".MainActivity"
            android:theme="@style/AppTheme.Fullscreen">
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value=".MainActivity" />
        </activity>
    </application>
</manifest>

Edit res/values/styles.xml.

<resources>
    <style name="AppTheme.Fullscreen">
        <item name="android:windowFullscreen">true</item>
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>
</resources>

Activity and layout

Code of ImageViewActivity.

ViewModel is used to maintain Dark Mode status to survice screen rotation/configuration change.

NOTE: Optional ViewModel and Dagger2 dependency injection is used. You can remove them.

class ImageViewActivity : AppCompatActivity() {    companion object {        private const val EXTRA_IMAGE_RESOURCE = "image_resource"        fun newInstance(context: Context, imageResource: String) = Intent(context, ImageViewActivity::class.java).apply {            // imageResource can be file path or URL            putExtra(EXTRA_IMAGE_RESOURCE, imageResource)        }    }    @Inject    lateinit var viewModelFactory: ViewModelFactory    private lateinit var viewModel: ImageViewViewModel    override fun onCreate(savedInstanceState: Bundle?) {        AndroidInjection.inject(this)        super.onCreate(savedInstanceState)        setContentView(R.layout.activity_image_view)        setSupportActionBar(toolbar)        supportActionBar?.setDisplayHomeAsUpEnabled(true)        viewModel = ViewModelProviders.of(this, viewModelFactory).get(ImageViewViewModel::class.java)        val imageResource = intent.getStringExtra(EXTRA_IMAGE_RESOURCE)        GlideApp.with(this)                .load(imageResource)                // .override(SimpleTarget.SIZE_ORIGINAL, SimpleTarget.SIZE_ORIGINAL)                .into(photoView)        photoView.setOnClickListener {            viewModel.darkMode.value = !(viewModel.darkMode.value ?: false)        }        viewModel.darkMode.observe(this, Observer {            it?.also {                val color = if (it) {                    toolbar.isVisible = false                    android.R.color.black                }                else {                    toolbar.isVisible = true                    android.R.color.white                }                container.setBackgroundColor(ContextCompat.getColor(context, color))            }        })    }    override fun onSupportNavigateUp(): Boolean {        onBackPressed()        return true    }}

class ImageViewViewModel @Inject constructor(private val db: AppDatabase): ViewModel() {    internal val darkMode = MutableLiveData<Boolean>()    init {        darkMode.value = false    }}

activity_image_view.xml

Change AppBarLayout to transparent background.
Don't apply app:layout_behavior="@string/appbar_scrolling_view_behavior" to content (ensure content can be fullscreen without restriction of AppBarLayout)
Put AppBarLayout after content (PhotoView), else toolbar button are not clickable.

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".view.support.ImageViewActivity">

    <!--
    <include layout="@layout/content_image_view" />
     -->

    <!-- app:layout_behavior="@string/appbar_scrolling_view_behavior" -->
    <com.github.chrisbanes.photoview.PhotoView
        android:id="@+id/photoView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:adjustViewBounds="true"
        android:scaleType="fitCenter"
        />

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay.Light"
        android:background="@android:color/transparent"
        app:elevation="0dp">

        <!-- android:background="?attr/colorPrimary" -->
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <!--
    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@android:drawable/ic_dialog_email" />
        -->

</android.support.design.widget.CoordinatorLayout>