1.22 Load existing pet data from database

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

@@ -15,8 +15,12 @@
  */
 package com.example.android.pets;
 
+import android.app.LoaderManager;
 import android.content.ContentValues;
+import android.content.CursorLoader;
 import android.content.Intent;
+import android.content.Loader;
+import android.database.Cursor;
 import android.net.Uri;
 import android.os.Bundle;
 import android.support.v4.app.NavUtils;
@@ -36,7 +40,14 @@
 /**
  * Allows user to create a new pet or edit an existing one.
  */
-public class EditorActivity extends AppCompatActivity {
+public class EditorActivity extends AppCompatActivity implements
+        LoaderManager.LoaderCallbacks<Cursor> {
+
+    /** Identifier for the pet data loader */
+    private static final int EXISTING_PET_LOADER = 0;
+
+    /** Content URI for the existing pet (null if it's a new pet) */
+    private Uri mCurrentPetUri;
 
     /** EditText field to enter the pet's name */
     private EditText mNameEditText;
@@ -65,16 +76,20 @@ protected void onCreate(Bundle savedInstanceState) {
         // Examine the intent that was used to launch this activity,
         // in order to figure out if we're creating a new pet or editing an existing one.
         Intent intent = getIntent();
-        Uri currentPetUri = intent.getData();
+        mCurrentPetUri = intent.getData();
 
         // If the intent DOES NOT contain a pet content URI, then we know that we are
         // creating a new pet.
-        if (currentPetUri == null) {
+        if (mCurrentPetUri == null) {
             // This is a new pet, so change the app bar to say "Add a Pet"
             setTitle(getString(R.string.editor_activity_title_new_pet));
         } else {
             // Otherwise this is an existing pet, so change app bar to say "Edit Pet"
             setTitle(getString(R.string.editor_activity_title_edit_pet));
+
+            // Initialize a loader to read the pet data from the database
+            // and display the current values in the editor
+            getLoaderManager().initLoader(EXISTING_PET_LOADER, null, this);
         }
 
         // Find all relevant views that we will need to read user input from
@@ -190,4 +205,77 @@ public boolean onOptionsItemSelected(MenuItem item) {
         }
         return super.onOptionsItemSelected(item);
     }
+
+    @Override
+    public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
+        // Since the editor shows all pet attributes, define a projection that contains
+        // all columns from the pet table
+        String[] projection = {
+                PetEntry._ID,
+                PetEntry.COLUMN_PET_NAME,
+                PetEntry.COLUMN_PET_BREED,
+                PetEntry.COLUMN_PET_GENDER,
+                PetEntry.COLUMN_PET_WEIGHT };
+
+        // This loader will execute the ContentProvider's query method on a background thread
+        return new CursorLoader(this,   // Parent activity context
+                mCurrentPetUri,         // Query the content URI for the current pet
+                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 cursor) {
+        // Bail early if the cursor is null or there is less than 1 row in the cursor
+        if (cursor == null || cursor.getCount() < 1) {
+            return;
+        }
+
+        // Proceed with moving to the first row of the cursor and reading data from it
+        // (This should be the only row in the cursor)
+        if (cursor.moveToFirst()) {
+            // Find the columns of pet attributes that we're interested in
+            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);
+
+            // Extract out the value from the Cursor for the given column index
+            String name = cursor.getString(nameColumnIndex);
+            String breed = cursor.getString(breedColumnIndex);
+            int gender = cursor.getInt(genderColumnIndex);
+            int weight = cursor.getInt(weightColumnIndex);
+
+            // Update the views on the screen with the values from the database
+            mNameEditText.setText(name);
+            mBreedEditText.setText(breed);
+            mWeightEditText.setText(Integer.toString(weight));
+
+            // Gender is a dropdown spinner, so map the constant value from the database
+            // into one of the dropdown options (0 is Unknown, 1 is Male, 2 is Female).
+            // Then call setSelection() so that option is displayed on screen as the current selection.
+            switch (gender) {
+                case PetEntry.GENDER_MALE:
+                    mGenderSpinner.setSelection(1);
+                    break;
+                case PetEntry.GENDER_FEMALE:
+                    mGenderSpinner.setSelection(2);
+                    break;
+                default:
+                    mGenderSpinner.setSelection(0);
+                    break;
+            }
+        }
+    }
+
+    @Override
+    public void onLoaderReset(Loader<Cursor> loader) {
+        // If the loader is invalidated, clear out all the data from the input fields.
+        mNameEditText.setText("");
+        mBreedEditText.setText("");
+        mWeightEditText.setText("");
+        mGenderSpinner.setSelection(0); // Select "Unknown" gender
+    }
 }