MvxExpandableRecyclerView.DroidX 2.0.0

Android MvxExpandableRecyclerView

This is an unofficial package that contains an expandable AndroidX RecyclerView supported for MvvmCross. This view allows us to bind a collection of items (objects, ViewModels, etc) to the ItemsSource property. It works similarly to a RecyclerView. However, this comes with out-of-the-box functionality such as grouping items with collapsible/expandable headers. Additional functionality can be implemented such as dragging items up and down and swiping them by attaching the provided ItemTouchHelperCallback to the RecyclerView.

All original functionality of MvxRecyclerView is also available and it is highly encouraged that you read the documentation before proceeding.

Getting Started

You need to ensure that you have the MvxExpandableRecyclerView.Core and MvxExpandableRecyclerView.DroidX NuGet packages installed in your .Core and .Droid projects respectively.

The general steps to implement this control:

1. We want to create an app where people are grouped by their appointment dates. Firstly, in our .Core project, we create an entity class to hold our data: Person.cs.

public class Person
{
  public Person(string firstName, string lastName, DateTime? appointment)
  {
    FirstName = firstName;
    LastName = lastName;
    Appointment = appointment;
  }

  public string FirstName { get; set; }

  public string LastName { get; set; }

  public DateTime? Appointment { get; set; }
}

2. We then create a class that inherits TaskItem<Person, DateTime?> named PersonItem.cs. This will allow the ExpandableRecyclerView to know how to group our Person.cs objects.

public class PersonItem : TaskItem<Person, DateTime?>
{
  public PersonItem(Person model) 
    : base(model)
  { }

  public override DateTime? Header { get => Model.Appointment; set => Model.Appointment = value; }
}

3. In our ViewModel (where we will add the ExpandableRecyclerView to the corresponding view), we will initialise a list that will hold PersonItems for binding.

public MvxObservableCollection<ITaskItem> People { get; private set; }

4. For the rest of the steps, everything will be done in our .Droid project. We create a view to display our PersonItem.cs objects inside the ExpandableRecyclerView. We'll name the view PersonItem.xml.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="horizontal"
  android:gravity="center">
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:MvxBind="Text Format('{0} {1} - {2:d}', Model.FirstName, Model.LastName, Model.Appointment);"/>
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginHorizontal="4sp"
    android:textColor="?android:attr/colorAccent"
    app:MvxBind="Text Sequence;"/>
</LinearLayout>

Notice that "Model" is prepended to our binded properties. This allows us to access properties in the underlying entity class. In this example, "Model" refers to the Person.cs entity class and we are binding Person.FirstName, Person.LastName and Person.Appointment to the TextView We also have another TextView that binds to TaskItem<TModel, THeader>.Sequence, if you want to save the ordering of each item.

5. We then create another view for our headers, if we want to display something other than a SimpleListItem1[^1]. In this example: TaskHeader.xml displays an ImageView showing an arrow up or down depending on the TaskHeader.IsCollapsed property and uses a TextView to bind to TaskHeader.Name. There's also another TextView that display the number of items under the said header.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="horizontal"
  android:padding="8sp"
  android:gravity="center">
  <FrameLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <ImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:src="@android:drawable/arrow_down_float"
      app:MvxBind="Visible IsCollapsed;"/>
    <ImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:src="@android:drawable/arrow_up_float"
      app:MvxBind="Visible !IsCollapsed;"/>
  </FrameLayout>
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    style="@style/Base.TextAppearance.AppCompat.Headline"
    app:MvxBind="Text Name;"/>
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginHorizontal="4sp"
    android:textColor="@android:color/holo_red_dark"
    app:MvxBind="Text Count;"/>
</LinearLayout>

6. We then create a custom Item Template Selector to handle displaying view for the corresponding item(s). In this example, if an item doesn't have a corresponding view, it will default to PersonItem.xml.

public class AppointmentTemplateSelector : MvxTemplateSelector<ITaskItem>
{
  public override int GetItemLayoutId(int fromViewType)
  {
    return fromViewType switch
    {
      1 => Resource.Layout.TaskHeader,
      _ => Resource.Layout.PersonItem,
    };
  }

  protected override int SelectItemViewType(ITaskItem forItemObject)
  {
    if (forItemObject is ITaskHeader)
      return 1;
    else
      return -1;
  }
}

7. Finally, adding MvxExpandableRecyclerView to one of your View.xml is very simple. In this example we have AppointmentView.xml and add:

<MvvmCross.ExpandableRecyclerView.DroidX.MvxExpandableRecyclerView
	android:id="@+id/appointment_recyclerview"
	android:layout_width="match_parent"
	android:layout_height="match_parent"
	local:MvxTemplateSelector="AppointmentPlanner.Droid.Components.AppointmentTemplateSelector, AppointmentPlanner.Droid"
	local:MvxBind="ItemsSource People;
			ItemSwipeStart RemovePersonCommand;
			ItemSwipeEnd UnplanPersonCommand;"/>

Important: MvxExpandableRecyclerView will require you to bind an ObservableCollection<ITaskItem> to ItemsSource and will need to have your custom MvxTemplateSelector for it to display your headers and items correctly.

For more information, MvvmCross provides documentation for MvxTemplateSelector. If you want to display complex objects for both/either headers and/or items, it is strongly recommended to use MvxTemplateSelector to show different types of views.

Dragging and Swiping Items

To enable dragging and swiping features, we need to use ItemTouchHelperCallback and attach it to our MvxExpandableRecyclerView.

MvxExpandableRecyclerView expandableRecyclerView = _view.FindViewById<MvxExpandableRecyclerView>(Resource.Id.appointment_recyclerview);
// Attach our helper class to implement drag and swipe functionality.
ItemTouchHelperCallback itemMoveCallback = new ItemTouchHelperCallback(expandableRecyclerView.Adapter);
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(itemMoveCallback);
itemTouchHelper.AttachToRecyclerView(expandableRecyclerView);

Swipe actions are bindable and can have 2 different actions depending on the direction of the swipe. ItemSwipeStart and ItemSwipeEnd are bindable and are done in the same way as MvxRecyclerView's ItemClickCommand and ItemLongClickCommand.

[^1]: If you don’t provide an item template selector MvxExpandableRecyclerView will fall back to using a SimpleListItem1, which is a built in Android Resource. It will also just call ToString() on your item that you are supplying. A custom view should be used for headers, if items aren't grouped using a string.