create Master List Fragment with view holder pattern

app/src/main/AndroidManifest.xml

@@ -9,17 +9,14 @@
         android:supportsRtl="true"
         android:theme="@style/AppTheme">
 
-        <!-- Declare the MainActivity in the manifest and set it to launch upon opening this app -->
-        <activity android:name=".ui.MainActivity" >
+        <activity android:name=".ui.MainActivity">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
 
         <activity android:name=".ui.AndroidMeActivity" />
-
     </application>
 
-</manifest>
+</manifest>

app/src/main/java/com/example/android/android_me/ui/MainActivity.java

@@ -24,12 +24,9 @@
 // This activity is responsible for displaying the master list of all images
 public class MainActivity extends AppCompatActivity {
 
-
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
-
     }
-
 }

app/src/main/java/com/example/android/android_me/ui/MasterListAdapter.java

@@ -20,9 +20,10 @@
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.BaseAdapter;
-import android.widget.GridView;
 import android.widget.ImageView;
 
+import com.example.android.android_me.R;
+
 import java.util.List;
 
 
@@ -35,6 +36,7 @@ public class MasterListAdapter extends BaseAdapter {
 
     /**
      * Constructor method
+     *
      * @param imageIds The list of images to display
      */
     public MasterListAdapter(Context context, List<Integer> imageIds) {
@@ -60,25 +62,26 @@ public long getItemId(int i) {
         return 0;
     }
 
-    /**
-     * Creates a new ImageView for each item referenced by the adapter
-     */
     public View getView(final int position, View convertView, ViewGroup parent) {
-        ImageView imageView;
         if (convertView == null) {
-            // If the view is not recycled, this creates a new ImageView to hold an image
-            imageView = new ImageView(mContext);
-            // Define the layout parameters
-            imageView.setAdjustViewBounds(true);
-            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
-            imageView.setPadding(8, 8, 8, 8);
-        } else {
-            imageView = (ImageView) convertView;
+            convertView = View.inflate(mContext, R.layout.image_item, null);
+
+            final ImageView imageView = (ImageView) convertView.findViewById(R.id.image_item);
+            final ViewHolder viewHolder = new ViewHolder(imageView);
+            convertView.setTag(viewHolder);
         }
 
         // Set the image resource and return the newly created ImageView
-        imageView.setImageResource(mImageIds.get(position));
-        return imageView;
+        final ViewHolder viewHolder = (ViewHolder) convertView.getTag();
+        viewHolder.imageViewItem.setImageResource(mImageIds.get(position));
+        return convertView;
     }
 
+    private class ViewHolder {
+        private final ImageView imageViewItem;
+
+        ViewHolder(ImageView imageViewItem) {
+            this.imageViewItem = imageViewItem;
+        }
+    }
 }

app/src/main/java/com/example/android/android_me/ui/MasterListFragment.java

@@ -26,7 +26,6 @@
 import com.example.android.android_me.R;
 import com.example.android.android_me.data.AndroidImageAssets;
 
-
 // This fragment displays all of the AndroidMe images in one large list
 // The list appears as a grid of images
 public class MasterListFragment extends Fragment {
@@ -43,7 +42,7 @@ public View onCreateView(LayoutInflater inflater, ViewGroup container,
         final View rootView = inflater.inflate(R.layout.fragment_master_list, container, false);
 
         // Get a reference to the GridView in the fragment_master_list xml layout file
-        GridView gridView = (GridView) rootView.findViewById(R.id.images_grid_view);
+        GridView gridView = (GridView) rootView.findViewById(R.id.image_grid_view);
 
         // Create the adapter
         // This adapter takes in the context and an ArrayList of ALL the image resources to display
@@ -55,5 +54,4 @@ public View onCreateView(LayoutInflater inflater, ViewGroup container,
         // Return the root view
         return rootView;
     }
-
 }

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

@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--Copyright (C) 2017 The Android Open Source Project
+<?xml version="1.0" encoding="utf-8"?><!--Copyright (C) 2017 The Android Open Source Project
  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
@@ -10,8 +9,7 @@
  See the License for the specific language governing permissions and
  limitations under the License.-->
 
-<ScrollView
-    xmlns:android="http://schemas.android.com/apk/res/android"
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
@@ -32,21 +30,24 @@
 
         <!-- Three containers for each Android-Me body part -->
         <!-- This container holds the head BodyPartFragment of the custom Android-Me image -->
-        <FrameLayout android:id="@+id/head_container"
-        android:layout_width="match_parent"
-        android:layout_height="180dp"
-        android:scaleType="centerInside"/>
+        <FrameLayout
+            android:id="@+id/head_container"
+            android:layout_width="match_parent"
+            android:layout_height="180dp"
+            android:scaleType="centerInside" />
 
         <!-- The remaining containers for the body and leg BodyPartFragments -->
-        <FrameLayout android:id="@+id/body_container"
+        <FrameLayout
+            android:id="@+id/body_container"
             android:layout_width="match_parent"
             android:layout_height="180dp"
-            android:scaleType="centerInside"/>
+            android:scaleType="centerInside" />
 
-        <FrameLayout android:id="@+id/leg_container"
+        <FrameLayout
+            android:id="@+id/leg_container"
             android:layout_width="match_parent"
             android:layout_height="180dp"
-            android:scaleType="centerInside"/>
+            android:scaleType="centerInside" />
 
 
     </LinearLayout>

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

@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--Copyright (C) 2017 The Android Open Source Project
+<?xml version="1.0" encoding="utf-8"?><!--Copyright (C) 2017 The Android Open Source Project
  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
@@ -11,8 +10,7 @@
  limitations under the License.-->
 
 <!-- Display the static master list fragment -->
-<fragment
-    xmlns:android="http://schemas.android.com/apk/res/android"
+<fragment xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/master_list_fragment"
     android:name="com.example.android.android_me.ui.MasterListFragment"
     android:layout_width="match_parent"

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

@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--Copyright (C) 2017 The Android Open Source Project
+<?xml version="1.0" encoding="utf-8"?><!--Copyright (C) 2017 The Android Open Source Project
  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
@@ -11,10 +10,7 @@
  limitations under the License.-->
 
 <!-- This fragment layout displays just one image of an Android-Me body part -->
-<ImageView
-    xmlns:android="http://schemas.android.com/apk/res/android"
+<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/body_part_image_view"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
-
-</ImageView>
+    android:layout_height="match_parent" />

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

@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--Copyright (C) 2017 The Android Open Source Project
+<?xml version="1.0" encoding="utf-8"?><!--Copyright (C) 2017 The Android Open Source Project
  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
@@ -11,17 +10,15 @@
  limitations under the License.-->
 
 <!-- GridView that displays AndroidMe images -->
-<GridView
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    android:id="@+id/images_grid_view"
+<GridView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/image_grid_view"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content"
+    android:layout_height="match_parent"
     android:adjustViewBounds="true"
     android:columnWidth="180dp"
     android:gravity="center"
     android:horizontalSpacing="8dp"
     android:numColumns="3"
     android:padding="16dp"
     android:stretchMode="columnWidth"
-    android:verticalSpacing="8dp">
-</GridView>
+    android:verticalSpacing="8dp" />

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

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/image_item"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:adjustViewBounds="true"
+    android:padding="8dp"
+    android:scaleType="centerCrop" />