Fix translucent navbar for Android 10

When the status bar is _not_ hidden, past behavior was for the
navigation bar to be translucent. On Android 10 (SDK 29), it is opaque
black. This patch restores and improves upon past behavior by ensuring a
fully transparent nav bar when gesture controls are enabled (and
using the system-provided translucent scrim when 3-button navigation
is enabled).

To achieve this we need to switch from using
android:windowTranslucentNavigation to using android:navigationBarColor.
On Android 10, it appears android:windowDrawsSystemBarBackgrounds
must be set for android:navigationBarColor to have any affect.
(I wonder if this is related to being an AlertDialog.)
android:windowDrawsSystemBarBackgrounds is not supported in SDK < 21,
whereas this library supports SDK >= 19, so I've created a separate
styles.xml file for SDK >= 29.

Setting systemUiVisibility flags appears to be necessary to get
the transparent nav bar effect. It seems that setting
android:windowTranslucentNavigation was providing the same effect
as setting these flags, but now it needs to be done manually for
SDK >= 29 as android:windowTranslucentNavigation is not set.

Author: svank

imageviewer/src/main/java/com/stfalcon/imageviewer/viewer/dialog/ImageViewerDialog.kt

@@ -18,6 +18,8 @@ package com.stfalcon.imageviewer.viewer.dialog
 
 import android.content.Context
 import android.view.KeyEvent
+import android.view.View
+import android.view.WindowManager
 import android.widget.ImageView
 import androidx.appcompat.app.AlertDialog
 import com.stfalcon.imageviewer.R
@@ -39,6 +41,12 @@ internal class ImageViewerDialog<T>(
         else
             R.style.ImageViewerDialog_Default
 
+    private val dialogSystemUiVisibility: Int
+        get() = if (builderData.shouldStatusBarHide)
+            0
+        else
+            View.SYSTEM_UI_FLAG_LAYOUT_STABLE or View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
+
     init {
         setupViewerView()
         dialog = AlertDialog
@@ -50,6 +58,7 @@ internal class ImageViewerDialog<T>(
                 setOnShowListener { viewerView.open(builderData.transitionView, animateOpen) }
                 setOnDismissListener { builderData.onDismissListener?.onDismiss() }
             }
+        dialog.window?.decorView?.systemUiVisibility = dialogSystemUiVisibility
     }
 
     fun show(animate: Boolean) {

imageviewer/src/main/res/values-v29/styles.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    
+    <style name="ImageViewerDialog.Default" parent="ImageViewerDialog.DefaultBaseTheme">
+        <item name="android:windowDrawsSystemBarBackgrounds">true</item>
+        <item name="android:navigationBarColor">@android:color/transparent</item>
+    </style>
+    
+</resources>

imageviewer/src/main/res/values/styles.xml

@@ -5,8 +5,11 @@
 
     <style name="ImageViewerDialog.NoStatusBar" parent="android:Theme.Translucent.NoTitleBar.Fullscreen"/>
 
-    <style name="ImageViewerDialog.Default" parent="android:Theme.Translucent.NoTitleBar">
+    <style name="ImageViewerDialog.DefaultBaseTheme" parent="android:Theme.Translucent.NoTitleBar">
         <item name="android:windowTranslucentStatus">true</item>
+    </style>
+    
+    <style name="ImageViewerDialog.Default" parent="ImageViewerDialog.DefaultBaseTheme">
         <item name="android:windowTranslucentNavigation">true</item>
     </style>