Developing a new BaseAdapter template in Android

Question

UPDATED: No more bugs! Comment on the sample itself. Advantages and disadvantages. What do you like, what you do not do. What can be fixed. Still don't understand why I did this ... let me know (but read my post below)

I am working on creating a new design pattern for BaseAdapters on Android, and so far I really like how it works!

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I have a data structure that can contain all the necessary data for each object in a particular type of collection. I am creating specific implementations of the BaseAdapter with my own user interface layout that will be displayed to the user on the screen. Pretty simple and great idea ... nothing new.

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OK, so WHY do I want this?

The general idea is: 1) to ignore the implementation of the getView method and allow more amateur developers to easily create their own custom adapters and 2) to simplify and abstract as much as possible.

NOTE: in the last two parts of the code, I have only 3 things to implement (this makes sense). The inner class that is present in the current Holder template is the SetLayoutResource (...) method and the ExtractLayoutResources (...) method.

3 main reasons why I want this and think it’s good ... abstraction, abstraction, abstraction!

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ConcreteCustomAdapter.java

(A specific code example ... this is basically how everything will look !!! This is basically all you need to enter to create a new custom base adapter !!!)

public class ConcreteCustomAdapter extends BaseDataAdapter<Song, SongHolder> { public ConcreteCustomAdapter(Context context, int resource, Song[] data) { super(context, resource, data); // Give the base class a reference to the actual type of Holder class to use this.setViewHolder(new SongHolder()); } @Override protected void setLayoutResources(SongHolder holder, Song data) { // Set the View Holder objects properties with the current data holder.imgUiControl.setImageResource(data.thumbnail); holder.txtUiControl.setText(data.Name); } @Override protected void extractLayoutResources(View row, SongHolder holder) { // Convert XML UI component definitions into the static View Holder object holder.imgUiControl = (ImageView) row.findViewById(R.id.imgUiControl); holder.txtUiControl = (TextView) row.findViewById(R.id.txtUiControl); } // Class that holds all the UI component references static class SongHolder implements IHolder { ImageView imgUiControl; TextView txtUiControl; } } 

Song.java

(User created!)

 // Entity that holds ALL the data public class Song implements IData { public int thumbnail; public String Name; ... // Constructors, Getters, Setters ... } 

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LEISURE CODES TO SUPPORT GOALS

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IHolder.java

 // Current Adapter Pattern uses Holder Objects, this represents that and the data via interface public interface IHolder { interface IData { } } 

BaseDataAdapter.java

(User should not touch this)

 // D for Data....H for Holder (sorry not convention) public abstract class BaseDataAdapter<D extends IData, H extends IHolder> extends BaseAdapter { private Context context; private int layoutResourceID; private D data[] = null; private H holder = null; public BaseDataAdapter(Context context, int resource, D[] data) { //super(context, resource, data); this.layoutResourceID = resource; this.context = context; this.data = data; } @Override public View getView(int position, View convertView, ViewGroup parent) { //super.getView(position, convertView, parent); View row = convertView; if (row == null) { LayoutInflater newView = ((Activity) context).getLayoutInflater(); row = newView.inflate(this.layoutResourceID, parent, false); extractLayoutResources(row, holder); row.setTag(holder); } else { holder = (H) row.getTag(); } setLayoutResources(holder, data[position]); return row; } public void setViewHolder(H holder) { this.holder = holder; } abstract protected void setLayoutResources(H holder, D data); abstract protected void extractLayoutResources(View row, H holder); @Override public int getCount() { return this.data.length; } @Override public Object getItem(int position) { return this.data[position]; } @Override public long getItemId(int position) { return 0; } } 

Answer 1

I would do it like this:

 public abstract class TypedListAdapter<T, H extends TypedListAdapter.ViewHolder> extends BaseAdapter { private final int itemViewId; private List<T> data; public TypedAdapter(final int itemViewId) { this(itemViewId, null); } public TypedAdapter(final int itemViewId, final List<T> data) { this.itemViewId = itemViewId; this.data = preventNull(data); } private List<T> preventNull(final List<T> data) { return data == null ? Collections.<T>emptyList() : data; } public void setData(final List<T> data) { final List<T> nonNullData = preventNull(data); if (nonNullData != this.data) { this.data = nonNullData; notifyDataSetChanged(); } } @Override public int getCount() { return data.size(); } @Override public T getItem(final int position) { return data.get(position); } @Override public long getItemId(final int position) { return position; } @Override public View getView(final int position, final View convertView, final ViewGroup parent) { final H holder = obtainHolder(convertView, parent); bind(holder, getItem(position)); return holder.view; } protected abstract void bind(final H holder, final T item); private H obtainHolder(final View convertView, final ViewGroup parent) { if (convertView == null) { final View view = LayoutInflater.from(parent.getContext()).inflate(itemViewId, parent, false); return createHolder(view); } else { return (H) convertView.getTag(); } } protected abstract H createHolder(final View view); public static class ViewHolder { public final View view; public ViewHolder(final View view) { this.view = view; view.setTag(this); } } } 

An adapter implementation might look like this:

 public class SongListAdapter extends TypedListAdapter<Song, SongListAdapter.SongHolder> { public SongListAdapter(final int itemViewId) { super(itemViewId); } public SongListAdapter(final int itemViewId, final List<Song> data) { super(itemViewId, data); } @Override protected void bind(final SongHolder holder, final Song item) { holder.name.setText(item.getName()); holder.thumbnail.setImageResource(item.getThumbnail()); } @Override protected SongHolder createHolder(final View view) { return new SongHolder(view); } public static class SongHolder extends ViewHolder { public final ImageView thumbnail; public final TextView name; public SongHolder(final View view) { super(view); thumbnail = (ImageView) view.findViewById(R.id.thumbnail); name = (TextView) view.findViewById(R.id.name); } } } 

Answer 2

About the error in your SetLayoutResource method, you forgot to start IHolder.

  @Override protected void SetLayoutResource(IHolder holder, int position) { Song currentSong = data[position]; // ERRORS HERE: imgSongThumbnail and company cannot be resolved, or is not a field (in IHolder!) holder.imgSongThumbnail.setImageResource(currentSong.thumbnail); holder.txtSongName.setText(currentSong.Name); .... } 

Must be

  @Override protected void SetLayoutResource(IHolder holder, int position) { Song currentSong = data[position]; SongHolder songHolder = (IHolder) holder; // ERRORS HERE: imgSongThumbnail and company cannot be resolved, or is not a field (in IHolder!) songHolder.imgSongThumbnail.setImageResource(currentSong.thumbnail); songHolder.txtSongName.setText(currentSong.Name); .... } 

You can download the working example at the following link https://docs.google.com/file/d/0B5bbdw1x2IDET1YxZE4wdnpxZnc/edit?usp=sharing

Answer 3

First, some general notes:

• Method names must begin with a lowercase letter.
• Personally, I would recommend renaming your generic types for a better understanding. For T I would go with TData , and for V I would use something like VHolder

Now for the answer:

Since you are using generics, you should also use them in method signatures:

 abstract protected void setLayoutResource(THolder holder, int position); abstract protected THolder extractLayoutResources(ViewGroup parent, View row, THolder holder); 

Now you are done with this in your GeneralSongListAdapter

 @Override protected SongHolder ExtractLayoutResources(ViewGroup parent, View row, SongHolder holder) { 

Now you can access the fields directly without casting.

Also, I would recommend renaming your abstract methods. I don't think their current names correctly say what this method should do. If you look at the CursorAdapter , you will see createView and bindView that do exactly what you are doing. Perhaps use this name.