Enable text preview in dialog when dragging through seekbar

We use the heading of font scaling dialog to provide font size preview
when users are dragging through the seekbar and before they release
their fingers from the seekbar.

Bug: 274395502
Test: Manually - attach viideos to the bug
Test: atest FontScalingDialogTest
Change-Id: I3290d8c3560fea86453674bfb1f935ba6f709609

packages/SystemUI/res/values/dimens.xml

@@ -1553,6 +1553,9 @@
     <dimen name="status_bar_user_chip_end_margin">12dp</dimen>
     <dimen name="status_bar_user_chip_text_size">12sp</dimen>
 
+    <!-- System UI Dialog -->
+    <dimen name="dialog_title_text_size">24sp</dimen>
+
     <!-- Internet panel related dimensions -->
     <dimen name="internet_dialog_list_max_height">662dp</dimen>
     <!-- The height of the WiFi network in Internet panel. -->

packages/SystemUI/res/values/styles.xml

@@ -1041,7 +1041,7 @@
 
     <style name="TextAppearance.Dialog.Title" parent="@android:style/TextAppearance.DeviceDefault.Large">
         <item name="android:textColor">?android:attr/textColorPrimary</item>
-        <item name="android:textSize">24sp</item>
+        <item name="android:textSize">@dimen/dialog_title_text_size</item>
         <item name="android:fontFamily">@*android:string/config_headlineFontFamily</item>
         <item name="android:lineHeight">32sp</item>
         <item name="android:gravity">center</item>

packages/SystemUI/src/com/android/systemui/accessibility/fontscaling/FontScalingDialog.kt

@@ -21,6 +21,7 @@ import android.content.pm.ActivityInfo
 import android.content.res.Configuration
 import android.os.Bundle
 import android.provider.Settings
+import android.util.TypedValue
 import android.view.LayoutInflater
 import android.widget.Button
 import android.widget.SeekBar
@@ -49,8 +50,7 @@ class FontScalingDialog(
     private lateinit var seekBarWithIconButtonsView: SeekBarWithIconButtonsView
     private var lastProgress: Int = -1
 
-    private val configuration: Configuration =
-        Configuration(context.getResources().getConfiguration())
+    private val configuration: Configuration = Configuration(context.resources.configuration)
 
     override fun onCreate(savedInstanceState: Bundle?) {
         setTitle(R.string.font_scaling_dialog_title)
@@ -90,6 +90,10 @@ class FontScalingDialog(
                     if (!isTrackingTouch) {
                         // The seekbar progress is changed by icon buttons
                         changeFontSize(progress)
+                    } else {
+                        // Provide preview configuration for text instead of changing the system
+                        // font scale before users release their finger from the seekbar.
+                        createTextPreview(progress)
                     }
                 }
 
@@ -163,6 +167,20 @@ class FontScalingDialog(
         }
     }
 
+    /** Provides font size preview for text before putting the final settings to the system. */
+    fun createTextPreview(index: Int) {
+        val previewConfig = Configuration(configuration)
+        previewConfig.fontScale = strEntryValues[index].toFloat()
+
+        val previewConfigContext = context.createConfigurationContext(previewConfig)
+        previewConfigContext.theme.setTo(context.theme)
+
+        title.setTextSize(
+            TypedValue.COMPLEX_UNIT_PX,
+            previewConfigContext.resources.getDimension(R.dimen.dialog_title_text_size)
+        )
+    }
+
     companion object {
         private const val ON = "1"
         private const val OFF = "0"

packages/SystemUI/tests/src/com/android/systemui/accessibility/fontscaling/FontScalingDialogTest.kt

@@ -185,4 +185,29 @@ class FontScalingDialogTest : SysuiTestCase() {
 
         fontScalingDialog.dismiss()
     }
+
+    @Test
+    fun dragSeekBar_createTextPreview() {
+        val slider: SeekBarWithIconButtonsView = spy(SeekBarWithIconButtonsView(mContext))
+        whenever(
+                fontScalingDialog.findViewById<SeekBarWithIconButtonsView>(R.id.font_scaling_slider)
+            )
+            .thenReturn(slider)
+        fontScalingDialog.show()
+        verify(slider).setOnSeekBarChangeListener(capture(seekBarChangeCaptor))
+        val seekBar: SeekBar = slider.findViewById(R.id.seekbar)!!
+
+        // Default seekbar progress for font size is 1, simulate dragging to 0 without
+        // releasing the finger
+        seekBarChangeCaptor.value.onStartTrackingTouch(seekBar)
+        seekBarChangeCaptor.value.onProgressChanged(
+            seekBar,
+            /* progress= */ 0,
+            /* fromUser= */ false
+        )
+        backgroundExecutor.runAllReady()
+
+        verify(fontScalingDialog).createTextPreview(/* index= */ 0)
+        fontScalingDialog.dismiss()
+    }
 }