Small bugfixes and better performance

app/src/main/java/com/kabouzeid/gramophone/adapter/PagerAdapter.java

@@ -0,0 +1,134 @@
+package com.kabouzeid.gramophone.adapter;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.support.v4.app.Fragment;
+import android.support.v4.app.FragmentManager;
+import android.support.v4.app.FragmentPagerAdapter;
+import android.util.SparseArray;
+import android.view.ViewGroup;
+
+import com.kabouzeid.gramophone.R;
+import com.kabouzeid.gramophone.ui.fragments.mainactivityfragments.AlbumViewFragment;
+import com.kabouzeid.gramophone.ui.fragments.mainactivityfragments.ArtistViewFragment;
+import com.kabouzeid.gramophone.ui.fragments.mainactivityfragments.PlaylistViewFragment;
+import com.kabouzeid.gramophone.ui.fragments.mainactivityfragments.SongViewFragment;
+
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+
+public class PagerAdapter extends FragmentPagerAdapter {
+
+    private final SparseArray<WeakReference<Fragment>> mFragmentArray = new SparseArray<>();
+
+    private final List<Holder> mHolderList = new ArrayList<>();
+
+    private final Context mContext;
+
+    private int mCurrentPage;
+
+    private String[] titles;
+
+    public PagerAdapter(final Context context, final FragmentManager fragmentManager) {
+        super(fragmentManager);
+        mContext = context;
+        titles = new String[]{
+                context.getResources().getString(R.string.songs),
+                context.getResources().getString(R.string.albums),
+                context.getResources().getString(R.string.artists),
+                context.getResources().getString(R.string.playlists)
+        };
+    }
+
+    @SuppressWarnings("synthetic-access")
+    public void add(final Class<? extends Fragment> className, final Bundle params) {
+        final Holder mHolder = new Holder();
+        mHolder.mClassName = className.getName();
+        mHolder.mParams = params;
+
+        final int mPosition = mHolderList.size();
+        mHolderList.add(mPosition, mHolder);
+        notifyDataSetChanged();
+    }
+
+    public Fragment getFragment(final int position) {
+        final WeakReference<Fragment> mWeakFragment = mFragmentArray.get(position);
+        if (mWeakFragment != null && mWeakFragment.get() != null) {
+            return mWeakFragment.get();
+        }
+        return getItem(position);
+    }
+
+    @Override
+    public Object instantiateItem(final ViewGroup container, final int position) {
+        final Fragment mFragment = (Fragment) super.instantiateItem(container, position);
+        final WeakReference<Fragment> mWeakFragment = mFragmentArray.get(position);
+        if (mWeakFragment != null) {
+            mWeakFragment.clear();
+        }
+        mFragmentArray.put(position, new WeakReference<Fragment>(mFragment));
+        return mFragment;
+    }
+
+    @Override
+    public Fragment getItem(final int position) {
+        final Holder mCurrentHolder = mHolderList.get(position);
+        final Fragment mFragment = Fragment.instantiate(mContext,
+                mCurrentHolder.mClassName, mCurrentHolder.mParams);
+        return mFragment;
+    }
+
+    @Override
+    public void destroyItem(final ViewGroup container, final int position, final Object object) {
+        super.destroyItem(container, position, object);
+        final WeakReference<Fragment> mWeakFragment = mFragmentArray.get(position);
+        if (mWeakFragment != null) {
+            mWeakFragment.clear();
+        }
+    }
+
+    @Override
+    public int getCount() {
+        return mHolderList.size();
+    }
+
+    @Override
+    public CharSequence getPageTitle(final int position) {
+        return titles[position]
+                .toUpperCase(Locale.getDefault());
+    }
+
+    public int getCurrentPage() {
+        return mCurrentPage;
+    }
+
+    protected void setCurrentPage(final int currentPage) {
+        mCurrentPage = currentPage;
+    }
+
+    public enum MusicFragments {
+        SONG(SongViewFragment.class),
+        ALBUM(AlbumViewFragment.class),
+        ARTIST(ArtistViewFragment.class),
+        PLAYLIST(PlaylistViewFragment.class);
+
+        private Class<? extends Fragment> mFragmentClass;
+
+        MusicFragments(final Class<? extends Fragment> fragmentClass) {
+            mFragmentClass = fragmentClass;
+        }
+
+        public Class<? extends Fragment> getFragmentClass() {
+            return mFragmentClass;
+        }
+
+    }
+
+    private final static class Holder {
+        String mClassName;
+
+        Bundle mParams;
+    }
+}