Use "empty presentation" slide as default slide.

Since Presentation initializes slides via setSlides(), it's possible for the
presentation to have no slides (e.g. if the presentation.xml is empty).
To avoid the odd crash, we use a default slide that explains the situation
to the user / developer.

Issue #14.

framework/res/layout-xlarge/slide_internal_empty_presentation.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright (C) 2011 Michael Imamura
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:orientation="vertical"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingTop="@dimen/title_frag_diff_height">
+
+    <TextView
+        style="@style/SlideText"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/slide_internal_empty_content"/>
+
+</LinearLayout>

framework/res/values/strings.xml

@@ -20,6 +20,9 @@
 
     <string name="title_slide_title">Title</string>
 
+    <string name="slide_internal_empty_content"
+        >The presentation is empty or there there was a problem loading the slides.</string>
+
     <string name="menu_title">Title Slide</string>
     <string name="menu_toc">Table of Contents</string>
     <string name="menu_about">About</string>

framework/src/org/lugatgt/zoogie/present/Presentation.java

@@ -16,6 +16,7 @@
 
 package org.lugatgt.zoogie.present;
 
+import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
@@ -26,6 +27,9 @@
 import android.text.SpannableStringBuilder;
 import android.util.AttributeSet;
 
+import org.lugatgt.zoogie.present.slide.EmptyPresentationSlide;
+import org.lugatgt.zoogie.present.ui.SlideFragment;
+
 
 /**
  * Base class for presentations.
@@ -36,7 +40,14 @@ public class Presentation {
     private static final String PROP_PFX = "presentation.";
     private static final String PROP_INDEX = PROP_PFX + "index";
 
-    private List<Slide> slides;
+    private static final List<Slide> DEFAULT_SLIDES;
+    static {
+        List<Slide> slides = new ArrayList<Slide>(1);
+        slides.add(new EmptyPresentationSlideInfo());
+        DEFAULT_SLIDES = slides;
+    }
+
+    private List<Slide> slides = DEFAULT_SLIDES;
     private Map<String, Integer> nameToIndex;
 
     private OnIndexChangedListener indexChangedListener;
@@ -58,6 +69,7 @@ public Presentation() {
      */
     public Presentation(AttributeSet attrs) {
         idx = 0;
+        nameToIndex = new HashMap<String, Integer>();
     }
 
     // FIELD ACCESS ////////////////////////////////////////////////////////////
@@ -70,13 +82,18 @@ public Presentation(AttributeSet attrs) {
      * @param slides The list of slides (may not be null, may not be empty).
      */
     public void setSlides(List<? extends Slide> slides) {
+        //TODO: Properly support changing the slide list multiple times.
+        if (this.slides != DEFAULT_SLIDES) {
+            throw new IllegalArgumentException("setSlides() can only be called once.");
+        }
+
         if (slides == null || slides.isEmpty()) {
             throw new IllegalArgumentException("Slide list must not be empty.");
         }
 
         this.slides = new ArrayList<Slide>(slides);
 
-        nameToIndex = new HashMap<String, Integer>();
+        nameToIndex.clear();
         int i = 0;
         for (Slide slide : slides) {
             nameToIndex.put(slide.getName(), i);
@@ -233,4 +250,38 @@ public interface OnIndexChangedListener {
 
     }
 
+    ////////////////////////////////////////////////////////////////////////////
+    // EmptyPresentationSlide
+
+    private static class EmptyPresentationSlideInfo implements Slide {
+
+        @Override
+        public String getName() {
+            return "_empty";
+        }
+
+        @Override
+        public CharSequence getTitle(Context ctx) {
+            return "";
+        }
+
+        @Override
+        public CharSequence getSubtitle(Context ctx) {
+            return null;
+        }
+
+        @Override
+        public SlideFragment createFragment()
+            throws InstantiationException, IllegalAccessException, InvocationTargetException
+        {
+            return new EmptyPresentationSlide();
+        }
+
+        @Override
+        public SlideTransition getTransition() {
+            return null;
+        }
+
+    }
+
 }

framework/src/org/lugatgt/zoogie/present/slide/EmptyPresentationSlide.java

@@ -0,0 +1,23 @@
+package org.lugatgt.zoogie.present.slide;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import org.lugatgt.zoogie.present.R;
+import org.lugatgt.zoogie.present.ui.SlideFragment;
+
+
+/**
+ * "Dummy" slide used when the presentation has no slides.
+ * @author Michael Imamura
+ */
+public class EmptyPresentationSlide extends SlideFragment {
+
+    @Override
+    protected View onCreateContentView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
+        return inflater.inflate(R.layout.slide_internal_empty_presentation, null);
+    }
+
+}