Settings: Added preference fragment to the last tab in the main view.

This is a little bit flakey at this point, because the weird asynchronous nature of
adding fragments. If swiping to the second-to-last entry on the bottom navigation view,
it will populate the settings fragment in the UI and then it will dissapear. Need to
fix this.

app/src/main/java/org/fdroid/fdroid/views/main/MainViewController.java

@@ -1,6 +1,7 @@
 package org.fdroid.fdroid.views.main;
 
 import android.content.Intent;
+import android.support.v4.app.Fragment;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.RecyclerView;
 import android.view.View;
@@ -8,6 +9,7 @@ import android.widget.Button;
 import android.widget.FrameLayout;
 
 import org.fdroid.fdroid.R;
+import org.fdroid.fdroid.views.fragments.PreferencesFragment;
 import org.fdroid.fdroid.views.myapps.MyAppsViewBinder;
 import org.fdroid.fdroid.views.swap.SwapWorkflowActivity;
 
@@ -72,6 +74,20 @@ class MainViewController extends RecyclerView.ViewHolder {
         });
     }
 
+    /**
+     * Attaches a {@link PreferencesFragment} to the view. Everything else is managed by the
+     * fragment itself, so no further work needs to be done by this view binder.
+     *
+     * Note: It is tricky to attach a {@link Fragment} to a view from this view holder. This is due
+     * to the way in which the {@link RecyclerView} will reuse existing views and ask us to
+     * put a settings fragment in there at arbitrary times. Usually it wont be the same view we
+     * attached the fragment to last time, which causes weirdness. The solution is to use code from
+     * the com.lsjwzh.widget.recyclerviewpager.FragmentStatePagerAdapter which manages this.
+     * The code has been ported to {@link SettingsView}.
+     *
+     * @see SettingsView
+     */
     public void bindSettingsView() {
+        activity.getLayoutInflater().inflate(R.layout.main_tab_settings, frame, true);
     }
 }

app/src/main/java/org/fdroid/fdroid/views/main/SettingsView.java

@@ -0,0 +1,89 @@
+package org.fdroid.fdroid.views.main;
+
+import android.annotation.TargetApi;
+import android.content.Context;
+import android.support.v4.app.Fragment;
+import android.support.v4.app.FragmentTransaction;
+import android.support.v7.app.AppCompatActivity;
+import android.util.AttributeSet;
+import android.widget.FrameLayout;
+
+import org.fdroid.fdroid.R;
+import org.fdroid.fdroid.views.fragments.PreferencesFragment;
+
+/**
+ * When attached to the window, the {@link PreferencesFragment} will be added. When detached from
+ * the window, the fragment will be removed.
+ *
+ * Based on code from https://github.com/lsjwzh/RecyclerViewPager/blob/master/lib/src/main/java/com/lsjwzh/widget/recyclerviewpager/FragmentStatePagerAdapter.java
+ * licensed under the Apache 2.0 license (https://github.com/lsjwzh/RecyclerViewPager/blob/master/LICENSE).
+ * @see android.support.v4.app.FragmentStatePagerAdapter Much of the code here was ported from this class.
+ */
+public class SettingsView extends FrameLayout {
+
+    private FragmentTransaction currentTransaction;
+
+    public SettingsView(Context context) {
+        super(context);
+        setId(R.id.preference_fragment_parent);
+    }
+
+    public SettingsView(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        setId(R.id.preference_fragment_parent);
+    }
+
+    public SettingsView(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+        setId(R.id.preference_fragment_parent);
+    }
+
+    @TargetApi(21)
+    public SettingsView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+        setId(R.id.preference_fragment_parent);
+    }
+
+    @Override
+    protected void onAttachedToWindow() {
+        super.onAttachedToWindow();
+
+        AppCompatActivity activity = (AppCompatActivity) getContext();
+        if (activity == null) {
+            throw new IllegalArgumentException("Cannot add a SettingsView to activities which are not an AppCompatActivity");
+        }
+
+        if (currentTransaction == null) {
+            currentTransaction = activity.getSupportFragmentManager().beginTransaction();
+        }
+
+        currentTransaction.replace(getId(), new PreferencesFragment(), "preferences-fragment");
+        currentTransaction.commitAllowingStateLoss();
+        currentTransaction = null;
+        activity.getSupportFragmentManager().executePendingTransactions();
+    }
+
+    @Override
+    protected void onDetachedFromWindow() {
+        super.onDetachedFromWindow();
+
+        AppCompatActivity activity = (AppCompatActivity) getContext();
+        if (activity == null) {
+            throw new IllegalArgumentException("Cannot add a SettingsView to activities which are not an AppCompatActivity");
+        }
+
+        Fragment existingFragment = activity.getSupportFragmentManager().findFragmentByTag("preferences-fragment");
+        if (existingFragment == null) {
+            return;
+        }
+
+        if (currentTransaction == null) {
+            currentTransaction = activity.getSupportFragmentManager().beginTransaction();
+        }
+        currentTransaction.remove(existingFragment);
+        currentTransaction.commitAllowingStateLoss();
+        currentTransaction = null;
+        activity.getSupportFragmentManager().executePendingTransactions();
+    }
+
+}

app/src/main/res/layout/main_tab_settings.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<org.fdroid.fdroid.views.main.SettingsView
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+</org.fdroid.fdroid.views.main.SettingsView>

app/src/main/res/values/ids.xml

@@ -2,6 +2,7 @@
 <resources>
   <item type="id" name="category_spinner" />
   <item type="id" name="appDetailsSummaryHeader" />
+  <item type="id" name="preference_fragment_parent" />
 
   <item type="id" name="whats_new_feature" />
   <item type="id" name="whats_new_large_tile" />