The Model

The MVC Model component, shown in Listing 2-10, largely replaces the ToDoProvider.java code from before.

Listing 2-10.   MVC Model code

final class TodoModel
{
    private static final String DB_NAME = "tasks";
    private static final String TABLE_NAME = "tasks";
    private static final int DB_VERSION = 1;
    private static final String DB_CREATE_QUERY = "CREATE TABLE " + TodoModel.TABLE_NAME +
" (id integer primary key autoincrement, title text not null);";

    private final SQLiteDatabase storage;
    private final SQLiteOpenHelper helper;

    public TodoModel(final Context ctx)
    {
        this.helper = new SQLiteOpenHelper(ctx, TodoModel.DB_NAME, null, TodoModel.DB_VERSION)
        {
            @Override
            public void onCreate(final SQLiteDatabase db)
            {
                db.execSQL(TodoModel.DB_CREATE_QUERY);
            }

            @Override
            public void onUpgrade(final SQLiteDatabase db, final int oldVersion,
                                  final int newVersion)
            {
                db.execSQL("DROP TABLE IF EXISTS " + TodoModel.TABLE_NAME);
                this.onCreate(db);
            }
        };

        this.storage = this.helper.getWritableDatabase();
    }

    public void addEntry(ContentValues data)
    {
        this.storage.insert(TodoModel.TABLE_NAME, null, data);
    }

    public void deleteEntry(final String field_params)
    {
        this.storage.delete(TodoModel.TABLE_NAME, field_params, null);
    }

    public Cursor findAll()
    {
        Log.d(TodoActivity.APP_TAG, "findAll triggered");

        final Cursor c = this.storage.query(TodoModel.TABLE_NAME, new String[]
                { "title" }, null, null, null, null, null);

        return c;
    }
}

The View

The View code in MVC, shown in Listing 2-11, is a modified version of the ToDoActivity.java code from before. Any UI changes now happen here, and the control code is now moved to the ToDoController.java file.

Listing 2-11.   MVC View code

public class TodoActivity extends Activity
{
    public static final String APP_TAG = "com.example.mvc";

    private ListView taskView;
    private Button btNewTask;
    private EditText etNewTask;

    /*Controller changes are transparent to the View. UI changes won't
     *affect logic, and vice-versa. See below: the TodoModel has
     * been replaced with the TodoController, and the View persists
     * without knowledge that the implementation has changed.
     */
    private TodoController provider;

    private final OnClickListener handleNewTaskEvent = new OnClickListener()
    {
        @Override
        public void onClick(final View view)
        {
            Log.d(APP_TAG, "add task click received");

            TodoActivity.this.provider.addTask(TodoActivity.this
                    .etNewTask
                    .getText()
                    .toString());

            TodoActivity.this.renderTodos();
        }
    };

    @Override
    protected void onStop()
    {
        super.onStop();
    }

    @Override
    protected void onStart()
    {
        super.onStart();
    }

    @Override
    public void onCreate(final Bundle bundle)
    {
        super.onCreate(bundle);

        this.setContentView(R.layout.main);

        this.provider = new TodoController(this);
        this.taskView = (ListView) this.findViewById(R.id.tasklist);
        this.btNewTask = (Button) this.findViewById(R.id.btNewTask);
        this.etNewTask = (EditText) this.findViewById(R.id.etNewTask);
        this.btNewTask.setOnClickListener(this.handleNewTaskEvent);

        this.renderTodos();
    }

    private void renderTodos()
    {
        final List<String> beans = this.provider.getTasks();

        Log.d(TodoActivity.APP_TAG, String.format("%d beans found", beans.size()));

        this.taskView.setAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1,
                beans.toArray(new String[]
                        {})));

        this.taskView.setOnItemClickListener(new OnItemClickListener()
        {
            @Override
            public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id)
            {
                Log.d(TodoActivity.APP_TAG, String.format("item with id: %d and position: %d", id, position));

                final TextView v = (TextView) view;
                TodoActivity.this.provider.deleteTask(v.getText().toString());
                TodoActivity.this.renderTodos();
            }
        });
    }
}

The Controller

Shown in Listing 2-12, the controller binds the UI to the data but also creates a layer of separation between the model and view code above. This interface between the two layers provides a framework for the code to expand and for new developers to follow the MVC pattern to know what new code belongs where.

Listing 2-12.   MVC Controller code

public class TodoController {
    /*The Controller provides data from the Model for the View
     *to bind to the UI.
     */

    private TodoModel db_model;
    private List<String> tasks;

    public TodoController(Context app_context)
    {
        tasks = new ArrayList<String>();
        db_model = new TodoModel(app_context);
    }

    public void addTask(final String title)
    {
        final ContentValues data = new ContentValues();
        data.put("title", title);
        db_model.addEntry(data);
    }

    //Overrides to handle View specifics and keep Model straightforward.
    public void deleteTask(final String title)
    {
        db_model.deleteEntry("title='" + title + "'");
    }

    public void deleteTask(final long id)
    {
        db_model.deleteEntry("id='" + id + "'");
    }

    public void deleteAll()
    {
        db_model.deleteEntry(null);
    }

    public List<String> getTasks()
    {
        Cursor c = db_model.findAll();
        tasks.clear();

        if (c != null)
        {
            c.moveToFirst();

            while (c.isAfterLast() == false)
            {
                tasks.add(c.getString(0));
                c.moveToNext();
            }
            
            c.close();
        }

        return tasks;
    }
}

The Model

Shown in Listing 2-13, the Model largely stays the same in MVVM as it was in the MVC version.

Listing 2-13.   MVVM Model Code

package com.example.mvvm;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

final class TodoModel

{

    //The Model should contain no logic specific to the view - only
    //logic necessary to provide a minimal API to the ViewModel.
  private static final String DB_NAME = "tasks";
  private static final String TABLE_NAME = "tasks";
  private static final int DB_VERSION = 1;
  private static final String DB_CREATE_QUERY = "CREATE TABLE " + TodoModel.TABLE_NAME + " (id integer primary key autoincrement, title text not null);";

  private final SQLiteDatabase storage;
  private final SQLiteOpenHelper helper;
  public TodoModel(final Context ctx)

  {
    this.helper = new SQLiteOpenHelper(ctx, TodoModel.DB_NAME, null, TodoModel.DB_VERSION)
    {
       @Override
       public void onCreate(final SQLiteDatabase db)
       {
         db.execSQL(TodoModel.DB_CREATE_QUERY);
       }
       @Override
       public void onUpgrade(final SQLiteDatabase db, final int oldVersion,
           final int newVersion)
       {
         db.execSQL("DROP TABLE IF EXISTS " + TodoModel.TABLE_NAME);
         this.onCreate(db);
       }
    };
    this.storage = this.helper.getWritableDatabase();
  }

    /*Overrides are now done in the ViewModel. The Model only needs
     *to add/delete, and the ViewModel can handle the specific needs of the View.
     */
  public void addEntry(ContentValues data)
  {
    this.storage.insert(TodoModel.TABLE_NAME, null, data);
  }

  public void deleteEntry(final String field_params)
  {
    this.storage.delete(TodoModel.TABLE_NAME, field_params, null);
  }

  public Cursor findAll()
  {
        //Model only needs to return an accessor. The ViewModel will handle
         //any logic accordingly.
        return this.storage.query(TodoModel.TABLE_NAME, new String[]
    { "title" }, null, null, null, null, null);
  }
}

The View

The View, shown in Listing 2-14, in MVVM simply provides a reference to its elements.

Listing 2-14.   MVVM View Code

package com.example.mvvm;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;

public class TodoActivity extends Activity
{
  public static final String APP_TAG = "com.logicdrop.todos";

  private ListView taskView;
  private Button btNewTask;
  private EditText etNewTask;
    private TaskListManager delegate;

    /*The View handles UI setup only. All event logic and delegation
     *is handled by the ViewModel.
     */

    public static interface TaskListManager
    {
        //Through this interface the event logic is
        //passed off to the ViewModel.
        void registerTaskList(ListView list);
        void registerTaskAdder(View button, EditText input);
    }

  @Override
  protected void onStop()
  {
    super.onStop();
  }

  @Override
  protected void onStart()
  {
    super.onStart();
  }

  @Override
  public void onCreate(final Bundle bundle)
  {
    super.onCreate(bundle);

    this.setContentView(R.layout.main);

        this.delegate = new TodoViewModel(this);
        this.taskView = (ListView) this.findViewById(R.id.tasklist);
        this.btNewTask = (Button) this.findViewById(R.id.btNewTask);
        this.etNewTask = (EditText) this.findViewById(R.id.etNewTask);
        this.delegate.registerTaskList(taskView);
        this.delegate.registerTaskAdder(btNewTask, etNewTask);
  }
}

The ViewModel

The ViewModel component, shown in Listing 2-15, acts as a delegate between the ToDoActivity (View) and the ToDoProvider (Model). The ViewModel handles rendering and changes to the View’s data; it receives references from the View and uses them to update the UI.

Listing 2-15.   MVVM View-Model Code

package com.example.mvvm;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class TodoViewModel implements TodoActivity.TaskListManager
{
    /*The ViewModel acts as a delegate between the ToDoActivity (View)
     *and the ToDoProvider (Model).
     * The ViewModel receives references from the View and uses them
     * to update the UI.
     */

    private TodoModel db_model;
    private List<String> tasks;
    private Context main_activity;
    private ListView taskView;
    private EditText newTask;

    public TodoViewModel(Context app_context)
    {
        tasks = new ArrayList<String>();
        main_activity = app_context;
        db_model = new TodoModel(app_context);
    }

    //Overrides to handle View specifics and keep Model straightforward.

    private void deleteTask(View view)
    {
        db_model.deleteEntry("title='" + ((TextView)view).getText().toString() + "'");
    }

    private void addTask(View view)
    {
        final ContentValues data = new ContentValues();
        
        data.put("title", ((TextView)view).getText().toString());
        db_model.addEntry(data);
    }

    private void deleteAll()
    {
        db_model.deleteEntry(null);
    }

    private List<String> getTasks()
    {
        final Cursor c = db_model.findAll();
        tasks.clear();
        if (c != null)
        {
            c.moveToFirst();
            while (c.isAfterLast() == false)
            {
                tasks.add(c.getString(0));
                c.moveToNext();
            }
            
            c.close();
        }
        return tasks;
    }

    private void renderTodos()
    {
        //The ViewModel handles rendering and changes to the view's
        //data. The View simply provides a reference to its
        //elements.
        taskView.setAdapter(new ArrayAdapter<String>(main_activity,
                android.R.layout.simple_list_item_1,
                getTasks().toArray(new String[]
                        {})));
    }

    public void registerTaskList(ListView list)
    {
        this.taskView = list; //Keep reference for rendering later
        if (list.getAdapter() == null) //Show items at startup
        {
            renderTodos();
        }
        list.setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
            @Override
            public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id)
            { //Tapping on any item in the list will delete that item from the database and re-render the list
                deleteTask(view);
                renderTodos();
            }
        });
    }

    public void registerTaskAdder(View button, EditText input)
    {
        this.newTask = input;
        button.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(final View view)
            { //Add task to database, re-render list, and clear the input
                addTask(newTask);
                renderTodos();
                newTask.setText("");
            }
        });
    }
}

The ToDoModule

Listing 2-16 shows how the ToDoModule wires in the two database providers; the first is the real database and the second is a stub function.

Listing 2-16.   Dagger ToDoModule.java

import dagger.Module;
import dagger.Provides;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

@Module(complete = true, injects = { TodoActivity.class })
public class TodoModule {

   static final String DB_NAME = "tasks";
   static final String TABLE_NAME = "tasks";
   static final int DB_VERSION = 1;
   static final String DB_CREATE_QUERY = "CREATE TABLE "
          + TodoModule.TABLE_NAME
          + " (id integer primary key autoincrement, title text not null);";

   private final Context appContext;
   public static boolean sourceToggle = false;
   private TodoApplication parent;

   /** Constructs this module with the application context. */
   public TodoModule(TodoApplication app) {
       this.parent = app;
       this.appContext = app.getApplicationContext();
       
   }

   @Provides
   public Context provideContext() {
       return appContext;
   }

   /**
    * Needed because we need to provide an implementation to an interface, not a
    * class.
    *

    * @return
    */
   @Provides
   IDataProvider provideDataProvider(final SQLiteDatabase db) {
       //Here we obtain the boolean value for which provider to use
       boolean currentChoice = parent.getCurrentSource();
       if(currentChoice == true){
          //Here is a log message to know which provider has been chosen
          Log.d(TodoActivity.APP_TAG, "Provider2");
          return new TodoProvider2(db);
       }else{
          Log.d(TodoActivity.APP_TAG, "Provider");
          return new TodoProvider(db);
       }
   }

   /**
    * Needed because we need to configure the helper before injecting it.
    *
    * @return
    */
   @Provides
   SQLiteOpenHelper provideSqlHelper() {
       final SQLiteOpenHelper helper = new SQLiteOpenHelper(this.appContext,
              TodoModule.DB_NAME, null, TodoModule.DB_VERSION) {
          @Override
          public void onCreate(final SQLiteDatabase db) {
              db.execSQL(TodoModule.DB_CREATE_QUERY);
          }

          @Override
          public void onUpgrade(final SQLiteDatabase db,
                 final int oldVersion, final int newVersion) {
              db.execSQL("DROP TABLE IF EXISTS " + TodoModule.TABLE_NAME);
              this.onCreate(db);
          }
       };

       return helper;
   }

   @Provides
   SQLiteDatabase provideDatabase(SQLiteOpenHelper helper) {
       return helper.getWritableDatabase();
   }
}

The Database Provider

The Boolean currentChoice tells the code which database provider to use; we can connect either to the real database, ToDoProvider2, as shown in Listing 2-17, or the stub, ToDoProvider, as shown in Listing 2-18.

Listing 2-17.   Dagger ToDoProvider2.java

package com.example.dagger;

import java.util.ArrayList;
import java.util.List;

import javax.inject.Inject;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

class TodoProvider2 implements IDataProvider {

   private final SQLiteDatabase storage;

   @Inject
   public TodoProvider2(SQLiteDatabase db)
   {
       this.storage = db;
   }

   @Override
   public void addTask(final String title) {
       final ContentValues data = new ContentValues();
       data.put("title", title);
       this.storage.insert(TodoModule.TABLE_NAME, null, data);
   }

   @Override
   public void deleteAll() {
       this.storage.delete(TodoModule.TABLE_NAME, null, null);
   }

   @Override
   public void deleteTask(final long id) {
       this.storage.delete(TodoModule.TABLE_NAME, "id=" + id, null);
   }

   @Override
   public void deleteTask(final String title) {
       this.storage.delete(TodoModule.TABLE_NAME, "title='" + title + "'",
              null);
   }

   @Override
   public List<String> findAll() {
       Log.d(TodoActivity.APP_TAG, "findAll triggered");
       final List<String> tasks = new ArrayList<String>();

       final Cursor c = this.storage.query(TodoModule.TABLE_NAME,
              new String[] { "title" }, null, null, null, null, null);

       if (c != null) {
          c.moveToFirst();

          while (c.isAfterLast() == false) {
              tasks.add(c.getString(0));
              c.moveToNext();
          }

          c.close();
       }

       return tasks;
   }
}

The Stub Provider

Listing 2-18 shows the fake or stubbed out database; we include this to make sure we’re only testing our code and not the database connections.

Listing 2-18.   ToDoProvider.java

package com.example.dagger;

import java.util.ArrayList;
import java.util.List;

import javax.inject.Inject;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

class TodoProvider implements IDataProvider {

   private final SQLiteDatabase storage;

   @Inject
   public TodoProvider(SQLiteDatabase db)
   {
       this.storage = db;
   }

   @Override
   public void addTask(final String title) {
       final ContentValues data = new ContentValues();
       data.put("title", title);
       this.storage.insert(TodoModule.TABLE_NAME, null, data);
   }

   @Override
   public void deleteAll() {
       this.storage.delete(TodoModule.TABLE_NAME, null, null);
   }

   @Override
   public void deleteTask(final long id) {
       this.storage.delete(TodoModule.TABLE_NAME, "id=" + id, null);
   }

   @Override
   public void deleteTask(final String title) {
       this.storage.delete(TodoModule.TABLE_NAME, "title='" + title + "'",
              null);
   }

   @Override
   public List<String> findAll() {
       Log.d(TodoActivity.APP_TAG, "findAll triggered");

       final List<String> tasks = new ArrayList<String>();

       final Cursor c = this.storage.query(TodoModule.TABLE_NAME,
              new String[] { "title" }, null, null, null, null, null);

       if (c != null) {
          c.moveToFirst();

          while (c.isAfterLast() == false) {
              tasks.add(c.getString(0));
              c.moveToNext();
          }

          c.close();
       }

       return tasks;
   }
}

ToDoApplication

Finally we need to tell the code what code to inject. We do this in the getCurrentSource method of ToDoApplcation.java, shown in Listing 2-19. Ideally, we’d like to set this in a config file somewhere, but here it is hard-coded in a file.

Listing 2-19.   ToDoApplication.java

package com.example.dagger;
import android.app.Application;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import dagger.ObjectGraph;

public class TodoApplication extends Application {

   private ObjectGraph objectGraph;
   SharedPreferences settings;

   @Override
   public void onCreate()
   {
       super.onCreate();
       
       //Initializes the settings variable
       this.settings = getSharedPreferences("Settings", MODE_PRIVATE);
       Object[] modules = new Object[] {
              new TodoModule(this)
       };
       
       objectGraph = ObjectGraph.create(modules);
   }

   public ObjectGraph getObjectGraph() {
       return this.objectGraph;
   }

   //Method to update the settings
   public void updateSetting(boolean newChoice){
       Editor editor = this.settings.edit();
       editor.putBoolean("CurrentChoice", TodoModule.sourceToggle);
       editor.commit();
   }

   //Method to obtain the value of the provider setting
   public boolean getCurrentSource(){
       return this.settings.getBoolean("CurrentChoice", false);
   }
}