Lecture Mobile Application Development (119310)

Android Framework Basics

Agenda

• Framework Components Part IV - Advanced Lists
  • RecyclerView
  • LayoutManager
  • RecyclerView.ViewHolder
  • RecyclerView.Adapter

RecyclerView

• Part of Android Jetpack
• Must be added manually to gradle

dependencies {
    ...
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    ...
}  

RecyclerView

• Example RecyclerView Layout

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/list"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

LayoutManager

• Is responsible for measuring and positioning item views within a RecyclerView
• Can be used to implement a standard vertically scrolling list, a uniform grid, staggered grids, horizontally scrolling collections and more
• Several stock layout managers are provided for general use.

RecyclerView RecyclerView = (ListView) findViewById(R.id.list);
recyclerView.setLayoutManager(new LinearLayoutManager(context));

recyclerView.setLayoutManager(new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false));

recyclerView.setLayoutManager(new GridLayoutManager(context, 3));

RecyclerView.ViewHolder

• Describes an item view and metadata about its place within the RecyclerView
• Lets Adapter cache expensive View.findViewById(int) results
• Will be created and reused by RecyclerView.Adapter

public class ViewHolder extends RecyclerView.ViewHolder {
        public final View mView;
        public final TextView mItemNumberView;
        public final TextView mContentView;
        public DummyItem mItem;

        public ViewHolder(View view) {
            super(view);
            mView = view;
            mItemNumberView = (TextView) view.findViewById(R.id.item_number);
            mContentView = (TextView) view.findViewById(R.id.content);
        }
    }

RecyclerView.Adapter

• Forces yout to implement ViewHolder
• Creates view holders as needed

public class MyItemRecyclerViewAdapter extends RecyclerView.Adapter<MyItemRecyclerViewAdapter.ViewHolder> {

    private final List<DummyItem> mValues;

    public MyItemRecyclerViewAdapter(List<DummyItem> items, OnListFragmentInteractionListener listener) {
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.mItem = mValues.get(position);
        holder.mItemNumberView.setText(mValues.get(position).id);
        holder.mContentView.setText(mValues.get(position).content);
    }

    @Override
    public int getItemCount() {
        return mValues.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        ...
    }
}

RecyclerView Setup

RecyclerView RecyclerView = (ListView) findViewById(R.id.list);
recyclerView.setLayoutManager(new LinearLayoutManager(context));

// use this setting to improve performance if you know that changes
// in content do not change the layout size of the RecyclerView
recyclerView.setHasFixedSize(true);

recyclerView.setAdapter(new MyItemRecyclerViewAdapter(myItems));