Loader之二:CursorLoader基本实例 分类: H1_ANDROID 2013-11-16 10:50 5447人阅读 评论(0) 收藏



<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    tools:context=".MainActivity" >

        android:layout_height="match_parent" />



package com.example.android.content.loadercursor;

import android.app.Activity;
import android.app.ListFragment;
import android.app.LoaderManager;
import android.database.Cursor;
import android.os.Bundle;
import android.widget.SearchView;

 * The entry point to the CursorLoader sample. This sample demonstrates the use
 * of the {@link LoaderManager} to retrieve data from a {@link Cursor}. Here, a
 * list of contacts is displayed in a {@link ListFragment} and filtered using a
 * {@link SearchView} ActionBar item.
public class MainActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {



package com.example.android.content.loadercursor;

import android.app.ListFragment;
import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract.Contacts;
import android.view.View;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;

 * A {@link ListFragment} that shows the use of a {@link LoaderManager} to
 * display a list of contacts accessed through a {@link Cursor}.
 * (1)继承Fragment或者其子类,用于创建一个Fragment。实现LoaderManager.LoaderCallbacks接口,用于与Loader的交互
 * 。 官方文档: A callback interface for a client to interact with the LoaderManager.
 * For example, you use the onCreateLoader() callback method to create a new
 * loader.
public class CursorLoaderListFragment extends ListFragment implements
		LoaderManager.LoaderCallbacks<Cursor> {

	// This is the Adapter being used to display the list's data.
	SimpleCursorAdapter mAdapter;

	// The SearchView for doing filtering.
	SearchView mSearchView;

	 * (2)在Activity被创建时调用此方法。Called when the fragment's activity has been
	 * created and this fragment's view hierarchy instantiated. You typically
	 * initialize a Loader within the activity's onCreate() method, or within
	 * the fragment's onActivityCreated() method.
	public void onActivityCreated(Bundle savedInstanceState) {

		// Give some text to display if there is no data. In a real
		// application this would come from a resource.
		setEmptyText("No phone numbers");

		 * Create an empty adapter we will use to display the loaded data. The
		 * simple_list_item_2 layout contains two rows on top of each other
		 * (text1 and text2) that will show the contact's name and status.
		// (3)设置Fragment的顯示內容
		mAdapter = new SimpleCursorAdapter(getActivity(),
				android.R.layout.simple_list_item_2, null, new String[] {
						Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS },
				new int[] { android.R.id.text1, android.R.id.text2 }, 0);

		// Start out with a progress indicator.

		// Prepare the loader. Either re-connect with an existing one,
		// or start a new one.
		 * (4)創建一個Loader,此Loader用于為Fragment載入內容。You typically initialize a
		 * Loader within the activity's onCreate() method, or within the
		 * fragment's onActivityCreated() method.
		 * 此方法將自動調用LoaderManager.LoaderCallbacks接口的onCreateLoader方法。
		getLoaderManager().initLoader(0, null, this);


	 * An item has been clicked in the {@link ListView}. Display a toast with
	 * the tapped item's id.
	public void onListItemClick(ListView l, View v, int position, long id) {
		Toast.makeText(getActivity(), "Item clicked: " + id, Toast.LENGTH_LONG)

	// These are the Contacts rows that we will retrieve.
	static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] {
			Contacts._ID, Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS,
			Contacts.LOOKUP_KEY, };

	 * (5)Loader被創建時的操作,一般用于加載內容。In this example, the onCreateLoader() callback
	 * method creates a CursorLoader. You must build the CursorLoader using its
	 * constructor method, which requires the complete set of information needed
	 * to perform a query to the ContentProvider.
	 */public Loader<Cursor> onCreateLoader(int id, Bundle args) {
		// This is called when a new Loader needs to be created. This
		// sample only has one Loader, so we don't care about the ID.
		// First, pick the base URI to use depending on whether we are
		// currently filtering.
		Uri baseUri;
		baseUri = Contacts.CONTENT_URI;

		// Now create and return a CursorLoader that will take care of
		// creating a Cursor for the data being displayed.
		String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND ("
				+ Contacts.HAS_PHONE_NUMBER + "=1) AND ("
				+ Contacts.DISPLAY_NAME + " != '' ))";
		String order = Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC";

		return new CursorLoader(getActivity(), baseUri,
				CONTACTS_SUMMARY_PROJECTION, select, null, order);

	 * (6)内容被加载完成后的操作。The loader will release the data once it knows the
	 * application is no longer using it. For example, if the data is a cursor
	 * from a CursorLoader, you should not call close() on it yourself. If the
	 * cursor is being placed in a CursorAdapter, you should use the
	 * swapCursor() method so that the old Cursor is not closed.
	 */public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
		// Swap the new cursor in. (The framework will take care of closing the
		// old cursor once we return.)
		// Swap in a new Cursor, returning the old Cursor. Unlike
		// changeCursor(Cursor), the returned old Cursor is not closed.

		// The list should now be shown.
		if (isResumed()) {
		} else {

	// (7)Loader被重新加载时的操作。
	public void onLoaderReset(Loader<Cursor> loader) {
		// This is called when the last Cursor provided to onLoadFinished()
		// above is about to be closed. We need to make sure we are no
		// longer using it.