Fix flicker in Dark theme

Currently, when schedule sets to "Turns on at bedtime", the footer will
show a slid up animation when entering the page, this is because the
"Start time" & "End time" preferences are hidden in onResume().

This is because these 2 preferences always return AVAILABLE in
getAvailabilityStatus(), and manually update visibility in
refreshSummary(), which is called each time updateState() is called.

Usually the controller not set the visibility explicitly, but return
CONDITIONALLY_UNAVAILABLE in getAvailabilityStatus() when they want to
hide the preference.

Because getAvailabilityStatus() is called in onCreate(), by using this,
we can fix the flicker.

Fix: 234399017
Test: visual & robo test
Change-Id: I4cb7dd95d2985bd1ca4c8cb30aaebdc21a5415f8

src/com/android/settings/display/darkmode/DarkModeSettingsFragment.java

@@ -21,6 +21,7 @@ import android.os.Bundle;
 import android.os.PowerManager;
 
 import androidx.preference.Preference;
+import androidx.preference.PreferenceScreen;
 
 import com.android.settings.R;
 import com.android.settings.dashboard.DashboardFragment;
@@ -43,9 +44,6 @@ public class DarkModeSettingsFragment extends DashboardFragment {
     private DarkModeObserver mContentObserver;
     private DarkModeCustomPreferenceController mCustomStartController;
     private DarkModeCustomPreferenceController mCustomEndController;
-    private Runnable mCallback = () -> {
-        updatePreferenceStates();
-    };
     private static final int DIALOG_START_TIME = 0;
     private static final int DIALOG_END_TIME = 1;
 
@@ -60,7 +58,12 @@ public class DarkModeSettingsFragment extends DashboardFragment {
     public void onStart() {
         super.onStart();
         // Listen for changes only while visible.
-        mContentObserver.subscribe(mCallback);
+        mContentObserver.subscribe(() -> {
+            PreferenceScreen preferenceScreen = getPreferenceScreen();
+            mCustomStartController.displayPreference(preferenceScreen);
+            mCustomEndController.displayPreference(preferenceScreen);
+            updatePreferenceStates();
+        });
     }
 
     @Override