Automatically change order of days on pre-lollipop

app/src/main/java/org/isoron/uhabits/activities/habits/list/views/HeaderView.java

@@ -20,7 +20,6 @@
 package org.isoron.uhabits.activities.habits.list.views;
 
 import android.content.*;
-import android.graphics.*;
 import android.support.annotation.*;
 import android.util.*;
 import android.view.*;
@@ -32,7 +31,7 @@ import org.isoron.uhabits.utils.*;
 
 import java.util.*;
 
-public class HeaderView extends LinearLayout
+public class HeaderView extends LinearLayout implements Preferences.Listener
 {
     private final Context context;
 
@@ -52,13 +51,19 @@ public class HeaderView extends LinearLayout
         }
 
         Context appContext = context.getApplicationContext();
-        if(appContext instanceof HabitsApplication)
+        if (appContext instanceof HabitsApplication)
         {
             HabitsApplication app = (HabitsApplication) appContext;
             prefs = app.getComponent().getPreferences();
         }
     }
 
+    @Override
+    public void onCheckmarkOrderChanged()
+    {
+        createButtons();
+    }
+
     public void setButtonCount(int buttonCount)
     {
         this.buttonCount = buttonCount;
@@ -66,10 +71,28 @@ public class HeaderView extends LinearLayout
     }
 
     @Override
-    protected void onDraw(Canvas canvas)
+    protected void onAttachedToWindow()
+    {
+        super.onAttachedToWindow();
+        if (prefs != null) prefs.addListener(this);
+    }
+
+    @Override
+    protected void onDetachedFromWindow()
+    {
+        if (prefs != null) prefs.removeListener(this);
+        super.onDetachedFromWindow();
+    }
+
+    private void createButtons()
     {
+        removeAllViews();
         GregorianCalendar day = DateUtils.getStartOfTodayCalendar();
 
+        for (int i = 0; i < buttonCount; i++)
+            addView(
+                inflate(context, R.layout.list_habits_header_checkmark, null));
+
         for (int i = 0; i < getChildCount(); i++)
         {
             int position = i;
@@ -80,22 +103,11 @@ public class HeaderView extends LinearLayout
             label.setText(DateUtils.formatHeaderDate(day));
             day.add(GregorianCalendar.DAY_OF_MONTH, -1);
         }
-
-        super.onDraw(canvas);
-    }
-
-    private void createButtons()
-    {
-        int layout = R.layout.list_habits_header_checkmark;
-
-        removeAllViews();
-        for (int i = 0; i < buttonCount; i++)
-            addView(inflate(context, layout, null));
     }
 
     private boolean shouldReverseCheckmarks()
     {
-        if(prefs == null) return false;
+        if (prefs == null) return false;
         return prefs.shouldReverseCheckmarks();
     }
 }