Uses a custom state description for the Audio Balance seek bar.

This makes the seek bar more informative for a user of a screen reader
or other accessibility service. See context in b/319575109#comment7.

Bug: 319575109
Flag: com.android.settings.accessibility.audio_balance_state_description
Test: Use TalkBack to observe the state description while moving the
      seek bar.
Test: atest BalanceSeekBarTest
Change-Id: I7be15b26116f83854efe69d6b0560edde946daf5

src/com/android/settings/accessibility/BalanceSeekBar.java

@@ -20,6 +20,7 @@ import static android.view.HapticFeedbackConstants.CLOCK_TICK;
 
 import static com.android.settings.Utils.isNightMode;
 
+import android.annotation.StringRes;
 import android.content.Context;
 import android.content.res.ColorStateList;
 import android.content.res.Resources;
@@ -86,6 +87,14 @@ public class BalanceSeekBar extends SeekBar {
                 Settings.System.putFloatForUser(mContext.getContentResolver(),
                         Settings.System.MASTER_BALANCE, balance, UserHandle.USER_CURRENT);
             }
+            final int max = getMax();
+            if (Flags.audioBalanceStateDescription() && max > 0) {
+                seekBar.setStateDescription(createStateDescription(mContext,
+                        R.string.audio_seek_bar_state_left_first,
+                        R.string.audio_seek_bar_state_right_first,
+                        progress,
+                        max));
+            }
             // If fromUser is false, the call is a set from the framework on creation or on
             // internal update. The progress may be zero, ignore (don't change system settings).
 
@@ -161,5 +170,19 @@ public class BalanceSeekBar extends SeekBar {
         canvas.restore();
         super.onDraw(canvas);
     }
+
+    private static CharSequence createStateDescription(Context context,
+            @StringRes int resIdLeftFirst, @StringRes int resIdRightFirst,
+            int progress, float max) {
+        final boolean isLayoutRtl = context.getResources().getConfiguration().getLayoutDirection()
+                == LAYOUT_DIRECTION_RTL;
+        final int rightPercent = (int) (100 * (progress / max));
+        final int leftPercent = 100 - rightPercent;
+        if (rightPercent > leftPercent || (rightPercent == leftPercent && isLayoutRtl)) {
+            return context.getString(resIdRightFirst, rightPercent, leftPercent);
+        } else {
+            return context.getString(resIdLeftFirst, leftPercent, rightPercent);
+        }
+    }
 }