estsauver / adaptercommands Goto Github PK

#AdapterCommands Drop in solution to animate RecyclerView's dataset changes by using the command pattern for adapters with not stable ids. Read my blog post for more information.

Keep in mind that the runtime of DiffCommandsCalculator is O(n*m) (n = number of items in old list, m = number of items in new list). So you better run this on a background thread if your data set contains many items.

##Dependencies

compile 'com.hannesdorfmann.adaptercommands:adaptercommands:1.0.4'

There are basically 2 components:

• DiffCommandsCalculator that calculates the difference from previous data set to the new data set and returns List<AdapterCommand>. Please note that DiffCommandsCalculator is not thread safe. If you need a thread safe instance use ThreadSafeDiffCommandsCalculator.
• AdapterCommandProcessor takes List<AdapterCommand> and executes each command to trigger RecyclerView's ItemAnimator to run animations.

public class MainActivity extends AppCompatActivity {

  @Bind(R.id.recyclerView) RecyclerView recyclerView;

  List<Item> items = new ArrayList<Item>();
  Random random = new Random();
  ItemAdapter adapter; // RecyclerView adapter
  AdapterCommandProcessor commandProcessor;
  DiffCommandsCalculator<Item> commandsCalculator = new DiffCommandsCalculator<Item>();

  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.bind(this);

    adapter = new ItemAdapter(this, items);
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new GridLayoutManager(this, 4));

    commandProcessor = new AdapterCommandProcessor(adapter);
  }

  // Called when new items should be displayed in RecyclerView
  public void setItems(List<Item> newItems){
    adapter.setItems(newItems);
    List<AdapterCommand> commands = commandsCalculator.diff(newItems);
    commandProcessor.execute(commands); // executes commands that triggers animations
  }

Best practise is to use a PresentationModel and Model-View-Presenter. See my blog post for a concrete example.

• comparing items DiffCommandsCalculator uses standard java's equals() method to compare two items (one from old list, one from new list). So you have to override equals() and hashCode() in your model class (use IDE to generate that):

public class Item {

int id;
String text;

@Override public boolean equals(Object o) {
  if (this == o) return true;
  if (o == null || getClass() != o.getClass()) return false;

  Item item = (Item) o;

  return id == item.id;
}

@Override public int hashCode() {
  return id;
}

As you might have noticed, we only use Item.id for equals. The reason is that if we have this item in old list item { id = 1, text ="Foo"} and the same item with the same id in the new list {item { id = 1, text ="other"} we just want to compare this items by the id. What here has happened was that the item.text has been changed from new list to old list, but we still compare two items just by item.id since this is the property we use in equals().

However, when a item.text has been changed, we have to detect this too because we have to call adapter.notifyItemChanged(position) (ItemChangedCommand). So we can provide an ItemChangedDetector that we can pass as constructor argument to DiffCommandsCalculator:

class MyItemChangedDetector implements ItemChangedDetector<Item>() {
   @Override public boolean hasChanged(Item oldItem, Item newItem) {
     return !oldItem.text.equals(newItem.text);
   }
};

and then use it like this:

DiffCommandsCalculator<Item> calculator = new DiffCommandsCalculator<>(new MyItemChangedDetector());

• We also can specify what exactly should happen on the first time we use DiffCommandsCalculator (there is no old list to compare to). In this case we either could call adapter.notifyDatasetChanged() (EntireDatasetChangedCommand) which is the default behaviour or adapter.notifyItemRangeInserted(0, items.size()) (ItemRangeInsertedCommand) which then will run ItemAnimator so that items will animate in. You can specify the behaviour as constructor parameter DiffCommandsCalculator(boolean itemRangeInsertedOnFirstDiff): new DiffCommandsCalculator(false) uses EntireDatasetChangedCommand (no animations, equivalent to new DiffCommandsCalculator()) whereas new DiffCommandsCalculator(true) uses ItemRangeInsertedCommand (animations).

Copyright 2016 Hannes Dorfmann

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.