Loader之二：CursorLoader基本实例

参考APIDEMO：sdk\samples\android-19\content\LoaderCursor

1、创建主布局文件，里面只包含一个Fragment。

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/FrameLayout1"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context=".MainActivity" ><fragmentandroid:id="@+id/fragment_list"android:name="com.example.android.content.loadercursor.CursorLoaderListFragment"android:layout_width="match_parent"android:layout_height="match_parent" /></FrameLayout>

2、创建主Activity文件中的android:name加载相应的Fragment

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 {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}}

3、创建相应的Fragment

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 implementsLoaderManager.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.*/@Overridepublic void onActivityCreated(Bundle savedInstanceState) {super.onActivityCreated(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);setListAdapter(mAdapter);// Start out with a progress indicator.setListShown(false);// 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.*/@Overridepublic void onListItemClick(ListView l, View v, int position, long id) {Toast.makeText(getActivity(), "Item clicked: " + id, Toast.LENGTH_LONG).show();}// 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.mAdapter.swapCursor(data);// The list should now be shown.if (isResumed()) {setListShown(true);} else {setListShownNoAnimation(true);}}// (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.mAdapter.swapCursor(null);}}

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