Add support for granular conversation data changes.

paging/app/build.gradle

@@ -11,15 +11,19 @@ android {
 
         minSdkVersion MINIMUM_SDK
         targetSdkVersion TARGET_SDK
+        multiDexEnabled true
     }
 
     compileOptions {
+        coreLibraryDesugaringEnabled true
         sourceCompatibility JAVA_VERSION
         targetCompatibility JAVA_VERSION
     }
 }
 
 dependencies {
+    coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:1.1.5'
+
     implementation 'androidx.appcompat:appcompat:1.2.0'
     implementation 'com.google.android.material:material:1.2.1'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.4'

paging/app/src/main/java/org/signal/pagingtest/EventListener.java

@@ -0,0 +1,5 @@
+package org.signal.pagingtest;
+
+interface EventListener {
+  void onItemClicked(String key);
+}

paging/app/src/main/java/org/signal/pagingtest/Item.java

@@ -0,0 +1,11 @@
+package org.signal.pagingtest;
+
+public final class Item {
+  final String key;
+  final long   timestamp;
+
+  public Item(String key, long timestamp) {
+    this.key       = key;
+    this.timestamp = timestamp;
+  }
+}

paging/app/src/main/java/org/signal/pagingtest/MainActivity.java

@@ -1,8 +1,10 @@
 package org.signal.pagingtest;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.lifecycle.ViewModelProvider;
+import androidx.recyclerview.widget.DiffUtil;
 import androidx.recyclerview.widget.LinearLayoutManager;
 import androidx.recyclerview.widget.RecyclerView;
 
@@ -16,22 +18,26 @@ import org.signal.paging.PagingController;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
 
-public class MainActivity extends AppCompatActivity {
+public class MainActivity extends AppCompatActivity implements EventListener {
+
+  private MainViewModel viewModel;
 
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
 
-    MyAdapter           adapter       = new MyAdapter();
+    MyAdapter           adapter       = new MyAdapter(this);
     RecyclerView        list          = findViewById(R.id.list);
     LinearLayoutManager layoutManager = new LinearLayoutManager(this);
 
     list.setAdapter(adapter);
     list.setLayoutManager(layoutManager);
 
-    MainViewModel viewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MainViewModel.class);
+    viewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MainViewModel.class);
     adapter.setPagingController(viewModel.getPagingController());
     viewModel.getList().observe(this, newList -> {
       adapter.submitList(newList);
@@ -51,21 +57,30 @@ public class MainActivity extends AppCompatActivity {
       layoutManager.scrollToPosition(target);
     });
 
-    findViewById(R.id.append_btn).setOnClickListener(v -> {
-      viewModel.appendItems();
+    findViewById(R.id.prepend_btn).setOnClickListener(v -> {
+      viewModel.prependItems();
     });
   }
 
+  @Override
+  public void onItemClicked(String key) {
+    viewModel.onItemClicked(key);
+  }
+
   static class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
 
     private final static int TYPE_NORMAL      = 1;
     private final static int TYPE_PLACEHOLDER = -1;
 
-    private PagingController controller;
+    private final EventListener listener;
+    private final List<Item>    data;
 
-    private final List<String> data = new ArrayList<>();
+    private PagingController<String> controller;
+
+    public MyAdapter(@NonNull EventListener listener) {
+      this.listener = listener;
+      this.data     = new ArrayList<>();
 
-    public MyAdapter() {
       setHasStableIds(true);
     }
 
@@ -81,14 +96,18 @@ public class MainActivity extends AppCompatActivity {
 
     @Override
     public long getItemId(int position) {
-      return position;
+      Item item = getItem(position);
+      if (item != null) {
+        return item.key.hashCode();
+      } else {
+        return 0;
+      }
     }
 
     @Override
     public @NonNull MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
       switch (viewType) {
         case TYPE_NORMAL:
-          return new MyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false));
         case TYPE_PLACEHOLDER:
           return new MyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false));
         default:
@@ -98,24 +117,53 @@ public class MainActivity extends AppCompatActivity {
 
     @Override
     public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
-      holder.bind(getItem(position));
+      holder.bind(getItem(position), position, listener);
     }
 
-    private String getItem(int index) {
+    private Item getItem(int index) {
       if (controller != null) {
         controller.onDataNeededAroundIndex(index);
       }
       return data.get(index);
     }
 
-    void setPagingController(PagingController pagingController) {
+    void setPagingController(PagingController<String> pagingController) {
       this.controller = pagingController;
     }
 
-    void submitList(List<String> list) {
+    void submitList(List<Item> list) {
+      DiffUtil.DiffResult result = DiffUtil.calculateDiff(new DiffUtil.Callback() {
+        @Override
+        public int getOldListSize() {
+          return data.size();
+        }
+
+        @Override
+        public int getNewListSize() {
+          return list.size();
+        }
+
+        @Override
+        public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
+          String oldKey = Optional.ofNullable(data.get(oldItemPosition)).map(item -> item.key).orElse(null);
+          String newKey = Optional.ofNullable(list.get(newItemPosition)).map(item -> item.key).orElse(null);
+
+          return Objects.equals(oldKey, newKey);
+        }
+
+        @Override
+        public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
+          Long oldKey = Optional.ofNullable(data.get(oldItemPosition)).map(item -> item.timestamp).orElse(null);
+          Long newKey = Optional.ofNullable(list.get(newItemPosition)).map(item -> item.timestamp).orElse(null);
+
+          return Objects.equals(oldKey, newKey);
+        }
+      }, false);
+
+      result.dispatchUpdatesTo(this);
+
       data.clear();
       data.addAll(list);
-      notifyDataSetChanged();
     }
   }
 
@@ -128,8 +176,16 @@ public class MainActivity extends AppCompatActivity {
       textView = itemView.findViewById(R.id.text);
     }
 
-    void bind(@NonNull String s) {
-      textView.setText(s == null ? "PLACEHOLDER" : s);
+    void bind(@Nullable Item item, int position, @NonNull EventListener listener) {
+      if (item != null) {
+        textView.setText(position + " | " + item.key.substring(0, 13) + " | " + System.currentTimeMillis());
+        textView.setOnClickListener(v -> {
+          listener.onItemClicked(item.key);
+        });
+      } else {
+        textView.setText(position + " | PLACEHOLDER");
+        textView.setOnClickListener(null);
+      }
     }
   }
 }

paging/app/src/main/java/org/signal/pagingtest/MainDataSource.java

@@ -0,0 +1,71 @@
+package org.signal.pagingtest;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import org.signal.paging.PagedDataSource;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.UUID;
+
+class MainDataSource implements PagedDataSource<String, Item> {
+
+  private final List<Item> items = new ArrayList<>();
+
+  MainDataSource(int size) {
+    buildItems(size);
+  }
+
+  @Override
+  public int size() {
+    return items.size();
+  }
+
+  @Override
+  public @NonNull List<Item> load(int start, int length, @NonNull CancellationSignal cancellationSignal) {
+    try {
+      Thread.sleep(500);
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    }
+
+    return items.subList(start, start + length);
+  }
+
+  @Override
+  public @Nullable Item load(String key) {
+    return items.stream().filter(item -> item.key.equals(key)).findFirst().orElse(null);
+  }
+
+  @Override
+  public @NonNull String getKey(@NonNull Item item) {
+    return item.key;
+  }
+
+  public void updateItem(@NonNull String key) {
+    ListIterator<Item> iter = items.listIterator();
+    while (iter.hasNext()) {
+      if (iter.next().key.equals(key)) {
+        iter.set(new Item(key, System.currentTimeMillis()));
+        break;
+      }
+    }
+  }
+
+  public @NonNull String prepend() {
+    Item item = new Item(UUID.randomUUID().toString(), System.currentTimeMillis());
+    items.add(0, item);
+    return item.key;
+  }
+
+  private void buildItems(int size) {
+    items.clear();
+
+    for (int i = 0; i < size; i++) {
+      items.add(new Item(UUID.randomUUID().toString(), System.currentTimeMillis()));
+    }
+  }
+}

paging/app/src/main/java/org/signal/pagingtest/MainViewModel.java

@@ -4,71 +4,40 @@ import androidx.annotation.NonNull;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.ViewModel;
 
-import org.signal.paging.PagedDataSource;
 import org.signal.paging.PagingController;
 import org.signal.paging.PagingConfig;
 import org.signal.paging.PagedData;
 
-import java.util.ArrayList;
 import java.util.List;
 
 public class MainViewModel extends ViewModel {
 
-  private final PagedData<String> pagedData;
-  private final MyDataSource      dataSource;
+  private final PagedData<String, Item> pagedData;
+  private final MainDataSource          dataSource;
 
   public MainViewModel() {
-    this.dataSource = new MyDataSource(1000);
+    this.dataSource = new MainDataSource(1000);
     this.pagedData = PagedData.create(dataSource, new PagingConfig.Builder().setBufferPages(3)
                                                                             .setPageSize(25)
                                                                             .build());
   }
 
-  public @NonNull LiveData<List<String>> getList() {
+  public void onItemClicked(@NonNull String key) {
+    dataSource.updateItem(key);
+    pagedData.getController().onDataItemChanged(key);
+  }
+
+  public @NonNull LiveData<List<Item>> getList() {
     return pagedData.getData();
   }
 
-  public @NonNull PagingController getPagingController() {
+  public @NonNull PagingController<String> getPagingController() {
     return pagedData.getController();
   }
 
-  public void appendItems() {
-    dataSource.setSize(dataSource.size() + 1);
-    pagedData.getController().onDataInvalidated();
+  public void prependItems() {
+    String key = dataSource.prepend();
+    pagedData.getController().onDataItemInserted(key, 0);
   }
 
-  private static class MyDataSource implements PagedDataSource<String> {
-
-    private int size;
-
-    MyDataSource(int size) {
-      this.size = size;
-    }
-
-    public void setSize(int size) {
-      this.size = size;
-    }
-
-    @Override
-    public int size() {
-      return size;
-    }
-
-    @Override
-    public List<String> load(int start, int length, @NonNull CancellationSignal cancellationSignal) {
-      try {
-        Thread.sleep(500);
-      } catch (InterruptedException e) {
-        e.printStackTrace();
-      }
-
-      List<String> data = new ArrayList<>(length);
-
-      for (int i = 0; i < length; i++) {
-        data.add(String.valueOf(start + i) + "     (" + System.currentTimeMillis() + ")");
-      }
-
-      return data;
-    }
-  }
 }

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

@@ -53,10 +53,10 @@
           android:layout_height="wrap_content" />
 
       <com.google.android.material.button.MaterialButton
-          android:id="@+id/append_btn"
+          android:id="@+id/prepend_btn"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
-          android:text="Append" />
+          android:text="Prepend" />
 
     </LinearLayout>
 

paging/app/src/main/res/layout/item.xml

@@ -22,6 +22,7 @@
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:padding="8dp"
+        android:fontFamily="monospace"
         tools:text="Spider-Man"/>
 
   </androidx.cardview.widget.CardView>