Preserve position of ScrollableChart on configuration changes

Fixes #240

app/src/main/java/org/isoron/uhabits/activities/common/dialogs/HistoryEditorDialog.java

@@ -78,6 +78,8 @@ public class HistoryEditorDialog extends AppCompatDialogFragment
         {
             long id = savedInstanceState.getLong("habit", -1);
             if (id > 0) this.habit = habitList.getById(id);
+            historyChart.onRestoreInstanceState(
+                savedInstanceState.getParcelable("historyChart"));
         }
 
         int padding =
@@ -129,6 +131,7 @@ public class HistoryEditorDialog extends AppCompatDialogFragment
     public void onSaveInstanceState(Bundle outState)
     {
         outState.putLong("habit", habit.getId());
+        outState.putParcelable("historyChart", historyChart.onSaveInstanceState());
     }
 
     public void setController(@NonNull Controller controller)

app/src/main/java/org/isoron/uhabits/activities/common/views/BundleSavedState.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2017 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.activities.common.views;
+
+import android.os.*;
+import android.view.*;
+
+public class BundleSavedState extends View.BaseSavedState
+{
+    public static final Parcelable.Creator<BundleSavedState> CREATOR =
+        new Parcelable.Creator<BundleSavedState>()
+        {
+            @Override
+            public BundleSavedState createFromParcel(Parcel source)
+            {
+                return new BundleSavedState(source);
+            }
+
+            @Override
+            public BundleSavedState[] newArray(int size)
+            {
+                return new BundleSavedState[size];
+            }
+        };
+
+    final Bundle bundle;
+
+    public BundleSavedState(Parcelable superState, Bundle bundle)
+    {
+        super(superState);
+        this.bundle = bundle;
+    }
+
+    public BundleSavedState(Parcel source)
+    {
+        super(source);
+        this.bundle = source.readBundle();
+    }
+
+    @Override
+    public void writeToParcel(Parcel out, int flags)
+    {
+        super.writeToParcel(out, flags);
+        out.writeBundle(bundle);
+    }
+}

app/src/main/java/org/isoron/uhabits/activities/common/views/ScrollableChart.java

@@ -21,6 +21,7 @@ package org.isoron.uhabits.activities.common.views;
 
 import android.animation.*;
 import android.content.*;
+import android.os.*;
 import android.util.*;
 import android.view.*;
 import android.widget.*;
@@ -143,6 +144,29 @@ public abstract class ScrollableChart extends View
         this.scrollerBucketSize = scrollerBucketSize;
     }
 
+    @Override
+    public void onRestoreInstanceState(Parcelable state)
+    {
+        BundleSavedState bss = (BundleSavedState) state;
+        int x = bss.bundle.getInt("x");
+        int y = bss.bundle.getInt("y");
+        dataOffset = bss.bundle.getInt("dataOffset");
+        scroller.startScroll(0, 0, x, y, 0);
+        scroller.computeScrollOffset();
+        super.onRestoreInstanceState(bss.getSuperState());
+    }
+
+    @Override
+    public Parcelable onSaveInstanceState()
+    {
+        Parcelable superState = super.onSaveInstanceState();
+        Bundle bundle = new Bundle();
+        bundle.putInt("x", scroller.getCurrX());
+        bundle.putInt("y", scroller.getCurrY());
+        bundle.putInt("dataOffset", dataOffset);
+        return new BundleSavedState(superState, bundle);
+    }
+
     private void init(Context context)
     {
         detector = new GestureDetector(context, this);