参考APIDEMO：sdksamplesandroid-19contentLoaderCursor
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" >
<fragment
android: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 {
@Override
protected 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 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.
*/@Override
public 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.
*/
@Override
public 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);
}
}