Lesson four

app/src/main/AndroidManifest.xml

@@ -29,14 +29,17 @@
         </activity>
         <activity
             android:name=".EditorActivity"
-            android:label="@string/editor_activity_title_new_pet"
             android:theme="@style/EditorTheme"
             android:parentActivityName=".CatalogActivity" >
             <!-- Parent activity meta-data to support 4.0 and lower -->
             <meta-data
                 android:name="android.support.PARENT_ACTIVITY"
                 android:value=".CatalogActivity" />
         </activity>
+        <provider
+            android:name=".data.PetProvider"
+            android:authorities="com.example.android.pets"
+            android:exported="false" />
     </application>
 
 </manifest>

app/src/main/java/com/example/android/pets/CatalogActivity.java

@@ -15,28 +15,37 @@
  */
 package com.example.android.pets;
 
+import android.app.LoaderManager;
+import android.content.ContentUris;
 import android.content.ContentValues;
+import android.content.CursorLoader;
 import android.content.Intent;
+import android.content.Loader;
 import android.database.Cursor;
-import android.database.sqlite.SQLiteDatabase;
+import android.net.Uri;
 import android.os.Bundle;
 import android.support.design.widget.FloatingActionButton;
 import android.support.v7.app.AppCompatActivity;
+import android.util.Log;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
-import android.widget.TextView;
+import android.widget.AdapterView;
+import android.widget.ListView;
 
 import com.example.android.pets.data.PetContract.PetEntry;
-import com.example.android.pets.data.PetDbHelper;
 
 /**
  * Displays list of pets that were entered and stored in the app.
  */
-public class CatalogActivity extends AppCompatActivity {
+public class CatalogActivity extends AppCompatActivity implements
+        LoaderManager.LoaderCallbacks<Cursor> {
 
-    /** Database helper that will provide us access to the database */
-    private PetDbHelper mDbHelper;
+    /** Identifier for the pet data loader */
+    private static final int PET_LOADER = 0;
+
+    /** Adapter for the ListView */
+    PetCursorAdapter mCursorAdapter;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -53,98 +62,48 @@ public void onClick(View view) {
             }
         });
 
-        // To access our database, we instantiate our subclass of SQLiteOpenHelper
-        // and pass the context, which is the current activity.
-        mDbHelper = new PetDbHelper(this);
-    }
+        // Find the ListView which will be populated with the pet data
+        ListView petListView = (ListView) findViewById(R.id.list);
 
-    @Override
-    protected void onStart() {
-        super.onStart();
-        displayDatabaseInfo();
-    }
+        // Find and set empty view on the ListView, so that it only shows when the list has 0 items.
+        View emptyView = findViewById(R.id.empty_view);
+        petListView.setEmptyView(emptyView);
 
-    /**
-     * Temporary helper method to display information in the onscreen TextView about the state of
-     * the pets database.
-     */
-    private void displayDatabaseInfo() {
-        // Create and/or open a database to read from it
-        SQLiteDatabase db = mDbHelper.getReadableDatabase();
+        // Setup an Adapter to create a list item for each row of pet data in the Cursor.
+        // There is no pet data yet (until the loader finishes) so pass in null for the Cursor.
+        mCursorAdapter = new PetCursorAdapter(this, null);
+        petListView.setAdapter(mCursorAdapter);
 
-        // Define a projection that specifies which columns from the database
-        // you will actually use after this query.
-        String[] projection = {
-                PetEntry._ID,
-                PetEntry.COLUMN_PET_NAME,
-                PetEntry.COLUMN_PET_BREED,
-                PetEntry.COLUMN_PET_GENDER,
-                PetEntry.COLUMN_PET_WEIGHT };
-
-        // Perform a query on the pets table
-        Cursor cursor = db.query(
-                PetEntry.TABLE_NAME,   // The table to query
-                projection,            // The columns to return
-                null,                  // The columns for the WHERE clause
-                null,                  // The values for the WHERE clause
-                null,                  // Don't group the rows
-                null,                  // Don't filter by row groups
-                null);                   // The sort order
-
-        TextView displayView = (TextView) findViewById(R.id.text_view_pet);
-
-        try {
-            // Create a header in the Text View that looks like this:
-            //
-            // The pets table contains <number of rows in Cursor> pets.
-            // _id - name - breed - gender - weight
-            //
-            // In the while loop below, iterate through the rows of the cursor and display
-            // the information from each column in this order.
-            displayView.setText("The pets table contains " + cursor.getCount() + " pets.\n\n");
-            displayView.append(PetEntry._ID + " - " +
-                    PetEntry.COLUMN_PET_NAME + " - " +
-                    PetEntry.COLUMN_PET_BREED + " - " +
-                    PetEntry.COLUMN_PET_GENDER + " - " +
-                    PetEntry.COLUMN_PET_WEIGHT + "\n");
-
-            // Figure out the index of each column
-            int idColumnIndex = cursor.getColumnIndex(PetEntry._ID);
-            int nameColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_NAME);
-            int breedColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_BREED);
-            int genderColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_GENDER);
-            int weightColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_WEIGHT);
-
-            // Iterate through all the returned rows in the cursor
-            while (cursor.moveToNext()) {
-                // Use that index to extract the String or Int value of the word
-                // at the current row the cursor is on.
-                int currentID = cursor.getInt(idColumnIndex);
-                String currentName = cursor.getString(nameColumnIndex);
-                String currentBreed = cursor.getString(breedColumnIndex);
-                int currentGender = cursor.getInt(genderColumnIndex);
-                int currentWeight = cursor.getInt(weightColumnIndex);
-                // Display the values from each column of the current row in the cursor in the TextView
-                displayView.append(("\n" + currentID + " - " +
-                        currentName + " - " +
-                        currentBreed + " - " +
-                        currentGender + " - " +
-                        currentWeight));
+        // Setup the item click listener
+        petListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
+            @Override
+            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
+                // Create new intent to go to {@link EditorActivity}
+                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
+
+                // Form the content URI that represents the specific pet that was clicked on,
+                // by appending the "id" (passed as input to this method) onto the
+                // {@link PetEntry#CONTENT_URI}.
+                // For example, the URI would be "content://com.example.android.pets/pets/2"
+                // if the pet with ID 2 was clicked on.
+                Uri currentPetUri = ContentUris.withAppendedId(PetEntry.CONTENT_URI, id);
+
+                // Set the URI on the data field of the intent
+                intent.setData(currentPetUri);
+
+                // Launch the {@link EditorActivity} to display the data for the current pet.
+                startActivity(intent);
             }
-        } finally {
-            // Always close the cursor when you're done reading from it. This releases all its
-            // resources and makes it invalid.
-            cursor.close();
-        }
+        });
+
+        // Kick off the loader
+        getLoaderManager().initLoader(PET_LOADER, null, this);
     }
 
     /**
      * Helper method to insert hardcoded pet data into the database. For debugging purposes only.
      */
     private void insertPet() {
-        // Gets the database in write mode
-        SQLiteDatabase db = mDbHelper.getWritableDatabase();
-
         // Create a ContentValues object where column names are the keys,
         // and Toto's pet attributes are the values.
         ContentValues values = new ContentValues();
@@ -153,14 +112,19 @@ private void insertPet() {
         values.put(PetEntry.COLUMN_PET_GENDER, PetEntry.GENDER_MALE);
         values.put(PetEntry.COLUMN_PET_WEIGHT, 7);
 
-        // Insert a new row for Toto in the database, returning the ID of that new row.
-        // The first argument for db.insert() is the pets table name.
-        // The second argument provides the name of a column in which the framework
-        // can insert NULL in the event that the ContentValues is empty (if
-        // this is set to "null", then the framework will not insert a row when
-        // there are no values).
-        // The third argument is the ContentValues object containing the info for Toto.
-        long newRowId = db.insert(PetEntry.TABLE_NAME, null, values);
+        // Insert a new row for Toto into the provider using the ContentResolver.
+        // Use the {@link PetEntry#CONTENT_URI} to indicate that we want to insert
+        // into the pets database table.
+        // Receive the new content URI that will allow us to access Toto's data in the future.
+        Uri newUri = getContentResolver().insert(PetEntry.CONTENT_URI, values);
+    }
+
+    /**
+     * Helper method to delete all pets in the database.
+     */
+    private void deleteAllPets() {
+        int rowsDeleted = getContentResolver().delete(PetEntry.CONTENT_URI, null, null);
+        Log.v("CatalogActivity", rowsDeleted + " rows deleted from pet database");
     }
 
     @Override
@@ -178,13 +142,41 @@ public boolean onOptionsItemSelected(MenuItem item) {
             // Respond to a click on the "Insert dummy data" menu option
             case R.id.action_insert_dummy_data:
                 insertPet();
-                displayDatabaseInfo();
                 return true;
             // Respond to a click on the "Delete all entries" menu option
             case R.id.action_delete_all_entries:
-                // Do nothing for now
+                deleteAllPets();
                 return true;
         }
         return super.onOptionsItemSelected(item);
     }
+
+    @Override
+    public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
+        // Define a projection that specifies the columns from the table we care about.
+        String[] projection = {
+                PetEntry._ID,
+                PetEntry.COLUMN_PET_NAME,
+                PetEntry.COLUMN_PET_BREED };
+
+        // This loader will execute the ContentProvider's query method on a background thread
+        return new CursorLoader(this,   // Parent activity context
+                PetEntry.CONTENT_URI,   // Provider content URI to query
+                projection,             // Columns to include in the resulting Cursor
+                null,                   // No selection clause
+                null,                   // No selection arguments
+                null);                  // Default sort order
+    }
+
+    @Override
+    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
+        // Update {@link PetCursorAdapter} with this new cursor containing updated pet data
+        mCursorAdapter.swapCursor(data);
+    }
+
+    @Override
+    public void onLoaderReset(Loader<Cursor> loader) {
+        // Callback called when the data needs to be deleted
+        mCursorAdapter.swapCursor(null);
+    }
 }