Android 用SQLite 使用 CursorLoader 中的数据填充列表视图

我做了简单的测试应用程序基于此示例。有一个按钮，插入到数据库和列表视图的数据。都是在 MainActivity 中。在原来的代码是

restartLoader()

仅从调用

onResume()

，但它刷新列表视图时才

onResume()

被执行死刑。我把

restartLoader()

在结束了

displayListView()

和现在它显示新行在列表视图中后我按下按钮。但我不认为它是正确的解决方案。

public class MainActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor>{

private SimpleCursorAdapter dataAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

displayListView();

Button add = (Button) findViewById(R.id.add);
add.setOnClickListener(new View.OnClickListener() {

public void onClick(View v) {

ContentValues values = new ContentValues();
values.put(SensorsDb.KEY_TYPE, "wld");
values.put(SensorsDb.KEY_TITLE, "Basement Water Detector");
values.put(SensorsDb.KEY_SERIAL, "33");
values.put(SensorsDb.KEY_VALUE, "NO WATER");

getContentResolver().insert(MyContentProvider.CONTENT_URI,values);

displayListView();
}
});
}
@Override
protected void onResume() {
super.onResume();
//Starts a new or restarts an existing Loader in this manager
getSupportLoaderManager().restartLoader(0, null, MainActivity.this);
}

private void displayListView() {
// The desired columns to be bound
String[] columns = new String[] {
SensorsDb.KEY_TITLE,
SensorsDb.KEY_VALUE
};
// the XML defined views which the data will be bound to
int[] to = new int[] {
R.id.sensorTitle,
R.id.sensorState
};

// create an adapter from the SimpleCursorAdapter
dataAdapter = new SimpleCursorAdapter(this, R.layout.custom_row_view, null, columns, to, 0);
//Ensures a loader is initialized and active.
getSupportLoaderManager().initLoader(0, null,  this);
// get reference to the ListView
ListView listView = (ListView) findViewById(R.id.sensorList);
// Assign adapter to ListView
listView.setAdapter(dataAdapter);

getSupportLoaderManager().restartLoader(0, null, MainActivity.this);
}

// This is called when a new Loader needs to be created.
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
String[] projection = {
SensorsDb.KEY_ROWID,
SensorsDb.KEY_TYPE,
SensorsDb.KEY_TITLE,
SensorsDb.KEY_SERIAL,
SensorsDb.KEY_VALUE};
CursorLoader cursorLoader = new CursorLoader(this,
MyContentProvider.CONTENT_URI, projection, null, null, null);
return cursorLoader;
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {

dataAdapter.swapCursor(data);
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {

dataAdapter.swapCursor(null);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
有 MyContentProvider 类

public class MyContentProvider extends ContentProvider{

private MyDatabaseHelper dbHelper;

private static final int ALL_SENSORS = 1;
private static final int SINGLE_SENSOR = 2;

// authority is the symbolic name of your provider
// To avoid conflicts with other providers, you should use
// Internet domain ownership (in reverse) as the basis of your provider authority.
private static final String AUTHORITY = "com.example.contproctest.contentprovider";

// create content URIs from the authority by appending path to database table
public static final Uri CONTENT_URI =
Uri.parse("content://" + AUTHORITY + "/sensors");

// a content URI pattern matches content URIs using wildcard characters:
// *: Matches a string of any valid characters of any length.
// #: Matches a string of numeric characters of any length.
private static final UriMatcher uriMatcher;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(AUTHORITY, "sensors", ALL_SENSORS);
uriMatcher.addURI(AUTHORITY, "sensors/#", SINGLE_SENSOR);
}

// system calls onCreate() when it starts up the provider.
@Override
public boolean onCreate() {
// get access to the database helper
dbHelper = new MyDatabaseHelper(getContext());
return false;
}

//Return the MIME type corresponding to a content URI
@Override
public String getType(Uri uri) {

switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
return "vnd.android.cursor.dir/vnd.com.example.contproctest.contentprovider.sensors";
case SINGLE_SENSOR:
return "vnd.android.cursor.item/vnd.com.example.contproctest.contentprovider.sensors";
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
}

// The insert() method adds a new row to the appropriate table, using the values
// in the ContentValues argument. If a column name is not in the ContentValues argument,
// you may want to provide a default value for it either in your provider code or in
// your database schema.
@Override
public Uri insert(Uri uri, ContentValues values) {

SQLiteDatabase db = dbHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
//do nothing
break;
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
long id = db.insert(SensorsDb.SQLITE_TABLE, null, values);
getContext().getContentResolver().notifyChange(uri, null);
return Uri.parse(CONTENT_URI + "/" + id);
}

// The query() method must return a Cursor object, or if it fails,
// throw an Exception. If you are using an SQLite database as your data storage,
// you can simply return the Cursor returned by one of the query() methods of the
// SQLiteDatabase class. If the query does not match any rows, you should return a
// Cursor instance whose getCount() method returns 0. You should return null only
// if an internal error occurred during the query process.
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {

SQLiteDatabase db = dbHelper.getWritableDatabase();
SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
queryBuilder.setTables(SensorsDb.SQLITE_TABLE);

switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
//do nothing
break;
case SINGLE_SENSOR:
String id = uri.getPathSegments().get(1);
queryBuilder.appendWhere(SensorsDb.KEY_ROWID + "=" + id);
break;
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}

Cursor cursor = queryBuilder.query(db, projection, selection,
selectionArgs, null, null, sortOrder);
return cursor;

}

// The delete() method deletes rows based on the seletion or if an id is
// provided then it deleted a single row. The methods returns the numbers
// of records delete from the database. If you choose not to delete the data
// physically then just update a flag here.
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {

SQLiteDatabase db = dbHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
//do nothing
break;
case SINGLE_SENSOR:
String id = uri.getPathSegments().get(1);
selection = SensorsDb.KEY_ROWID + "=" + id
+ (!TextUtils.isEmpty(selection) ?
" AND (" + selection + ')' : "");
break;
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int deleteCount = db.delete(SensorsDb.SQLITE_TABLE, selection, selectionArgs);
getContext().getContentResolver().notifyChange(uri, null);
return deleteCount;
}

// The update method() is same as delete() which updates multiple rows
// based on the selection or a single row if the row id is provided. The
// update method returns the number of updated rows.
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
//do nothing
break;
case SINGLE_SENSOR:
String id = uri.getPathSegments().get(1);
selection = SensorsDb.KEY_ROWID + "=" + id
+ (!TextUtils.isEmpty(selection) ?
" AND (" + selection + ')' : "");
break;
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int updateCount = db.update(SensorsDb.SQLITE_TABLE, values, selection, selectionArgs);
getContext().getContentResolver().notifyChange(uri, null);
return updateCount;
}

}
解决方法 1:
你不需要调用 restartLoader 后在 CP 中插入新的数据，因为 CursorLoader 可以听您的数据和 (ContentProvider) 的数据源中发生更改时自动更新。尝试在调用 cursor.setNotificationUri() 之前返回 Cursor 从你 CP 的查询方法。

@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {

SQLiteDatabase db = dbHelper.getWritableDatabase();
SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
queryBuilder.setTables(SensorsDb.SQLITE_TABLE);

switch (uriMatcher.match(uri)) {
case ALL_SENSORS:
//do nothing
break;
case SINGLE_SENSOR:
String id = uri.getPathSegments().get(1);
queryBuilder.appendWhere(SensorsDb.KEY_ROWID + "=" + id);
break;
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}

Cursor cursor = queryBuilder.query(db, projection, selection,
selectionArgs, null, null, sortOrder);

cursor.setNotificationUri(getContext().getContentResolver(), uri);

return cursor;
}