MvxExpandableRecyclerView.Core 3.1.1

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 binding a boolean property to EnableDrag and EnableSwipe respectively.

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 control 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 MvxExpandableRecyclerView 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 will create a layout to display our PersonItem.cs objects inside the MvxExpandableRecyclerView. We'll name the layout 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 show the ordering of each item.

5. We then create another layout 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 using TaskHeader.Count.

<?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 layouts for the corresponding item(s). In this example, if an item doesn't have a corresponding layout, 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;"/>

Important: MvxExpandableRecyclerView will require you to bind a MvxObservableCollection<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 Items

To enable the dragging feature, we need to modify our xml and bind EnableDrag to true.

<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;
		 EnableDrag true;"/>

Swiping Items

To enable the swiping feature, we need to modify our xml and bind EnableSwipe to true.

<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;
		 EnableSwipe true;
		 ItemSwipeRight UnplanPersonCommand;
		 ItemSwipeLeft RemovePersonCommand;"/>

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

We can also show different backgrounds for an item depending on the swipe direction. In this example, we create 2 new layout files UnplanTaskItemBackground.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:tag="swipe_right_background"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="horizontal"
  android:gravity="start"
  android:background="@android:color/holo_green_light">
  <ImageView
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:layout_centerVertical="true"
    android:layout_marginRight="10sp"
    android:background="@drawable/abc_ic_ab_back_material"/>
</LinearLayout>

And DeleteTaskItemBackground.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:tag="swipe_left_background"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="horizontal"
  android:gravity="end"
  android:background="@android:color/holo_red_light">
  <ImageView
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:layout_centerVertical="true"
    android:layout_marginLeft="10sp"
    android:background="@drawable/abc_ic_clear_material"/>
</LinearLayout>

Important: The important thing to notice in these files is that each layout has an android:tag attribute. This is important for the control because it identifies which layout to show when swiping left or right, or not swiping at all. The android:tags needed for the control are android:tag="swipe_right_background" (show layout when swiping right), android:tag="swipe_left_background" (show layout when swiping left) and android:tag="swipe_foreground" (show layout for item when user is not swiping).

We then modify our PersonItem.xml to include these layouts and make sure to wrap everything in a FrameLayout, making sure the background layouts are added first. We also need to add android:tag="swipe_foreground" to the nested FrameLayout tag holding all our PersonItem bindings for it show the layout when the user isn't swiping.

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
  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">
  <include
    layout="@layout/unplantaskitembackground"/>
  <include
    layout="@layout/deletetaskitembackground"/>
  <FrameLayout
    android:tag="swipe_foreground"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white">
    <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:orientation="horizontal"
      android:gravity="center"
      android:background="@drawable/appointment_recyclerview_item_background"
      app:MvxBind="Selected IsSelected">
      <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>
  </FrameLayout>
</FrameLayout>

Hide Sticky Header

A sticky header is always shown by default, however we can hide the sticky header by modifying our xml and bind ShowStickyHeader to false.

<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;
		 ShowStickyHeader false;"/>

Android MvxExpandableRecyclerViewSample

The MvxExpandableRecyclerViewSample demonstrates how to implement the MvxExpandableRecyclerView package into a simple project.

[^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.