Java tutorial
/* * Copyright (C) 2006 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.app; import android.os.Bundle; import android.os.Handler; import android.view.View; import android.widget.AdapterView; import android.widget.ListAdapter; import android.widget.ListView; /** * An activity that displays a list of items by binding to a data source such as * an array or Cursor, and exposes event handlers when the user selects an item. * <p> * ListActivity hosts a {@link android.widget.ListView ListView} object that can * be bound to different data sources, typically either an array or a Cursor * holding query results. Binding, screen layout, and row layout are discussed * in the following sections. * <p> * <strong>Screen Layout</strong> * </p> * <p> * ListActivity has a default layout that consists of a single, full-screen list * in the center of the screen. However, if you desire, you can customize the * screen layout by setting your own view layout with setContentView() in * onCreate(). To do this, your own view MUST contain a ListView object with the * id "@android:id/list" (or {@link android.R.id#list} if it's in code) * <p> * Optionally, your custom view can contain another view object of any type to * display when the list view is empty. This "empty list" notifier must have an * id "android:id/empty". Note that when an empty view is present, the list view * will be hidden when there is no data to display. * <p> * The following code demonstrates an (ugly) custom screen layout. It has a list * with a green background, and an alternate red "no data" message. * </p> * * <pre> * <?xml version="1.0" encoding="utf-8"?> * <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" * android:orientation="vertical" * android:layout_width="match_parent" * android:layout_height="match_parent" * android:paddingLeft="8dp" * android:paddingRight="8dp"> * * <ListView android:id="@android:id/list" * android:layout_width="match_parent" * android:layout_height="match_parent" * android:background="#00FF00" * android:layout_weight="1" * android:drawSelectorOnTop="false"/> * * <TextView android:id="@android:id/empty" * android:layout_width="match_parent" * android:layout_height="match_parent" * android:background="#FF0000" * android:text="No data"/> * </LinearLayout> * </pre> * * <p> * <strong>Row Layout</strong> * </p> * <p> * You can specify the layout of individual rows in the list. You do this by * specifying a layout resource in the ListAdapter object hosted by the activity * (the ListAdapter binds the ListView to the data; more on this later). * <p> * A ListAdapter constructor takes a parameter that specifies a layout resource * for each row. It also has two additional parameters that let you specify * which data field to associate with which object in the row layout resource. * These two parameters are typically parallel arrays. * </p> * <p> * Android provides some standard row layout resources. These are in the * {@link android.R.layout} class, and have names such as simple_list_item_1, * simple_list_item_2, and two_line_list_item. The following layout XML is the * source for the resource two_line_list_item, which displays two data * fields,one above the other, for each list row. * </p> * * <pre> * <?xml version="1.0" encoding="utf-8"?> * <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" * android:layout_width="match_parent" * android:layout_height="wrap_content" * android:orientation="vertical"> * * <TextView android:id="@+id/text1" * android:textSize="16sp" * android:textStyle="bold" * android:layout_width="match_parent" * android:layout_height="wrap_content"/> * * <TextView android:id="@+id/text2" * android:textSize="16sp" * android:layout_width="match_parent" * android:layout_height="wrap_content"/> * </LinearLayout> * </pre> * * <p> * You must identify the data bound to each TextView object in this layout. The * syntax for this is discussed in the next section. * </p> * <p> * <strong>Binding to Data</strong> * </p> * <p> * You bind the ListActivity's ListView object to data using a class that * implements the {@link android.widget.ListAdapter ListAdapter} interface. * Android provides two standard list adapters: * {@link android.widget.SimpleAdapter SimpleAdapter} for static data (Maps), * and {@link android.widget.SimpleCursorAdapter SimpleCursorAdapter} for Cursor * query results. * </p> * <p> * The following code from a custom ListActivity demonstrates querying the * Contacts provider for all contacts, then binding the Name and Company fields * to a two line row layout in the activity's ListView. * </p> * * <pre> * public class MyListAdapter extends ListActivity { * * @Override * protected void onCreate(Bundle savedInstanceState){ * super.onCreate(savedInstanceState); * * // We'll define a custom screen layout here (the one shown above), but * // typically, you could just use the standard ListActivity layout. * setContentView(R.layout.custom_list_activity_view); * * // Query for all people contacts using the {@link android.provider.Contacts.People} convenience class. * // Put a managed wrapper around the retrieved cursor so we don't have to worry about * // requerying or closing it as the activity changes state. * mCursor = this.getContentResolver().query(People.CONTENT_URI, null, null, null, null); * startManagingCursor(mCursor); * * // Now create a new list adapter bound to the cursor. * // SimpleListAdapter is designed for binding to a Cursor. * ListAdapter adapter = new SimpleCursorAdapter( * this, // Context. * android.R.layout.two_line_list_item, // Specify the row template to use (here, two columns bound to the two retrieved cursor * rows). * mCursor, // Pass in the cursor to bind to. * new String[] {People.NAME, People.COMPANY}, // Array of cursor columns to bind to. * new int[] {android.R.id.text1, android.R.id.text2}); // Parallel array of which template objects to bind to those columns. * * // Bind to our new adapter. * setListAdapter(adapter); * } * } * </pre> * * @see #setListAdapter * @see android.widget.ListView */ public class ListActivity extends Activity { /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected ListAdapter mAdapter; /** * This field should be made private, so it is hidden from the SDK. * {@hide} */ protected ListView mList; private Handler mHandler = new Handler(); private boolean mFinishedStart = false; private Runnable mRequestFocus = new Runnable() { public void run() { mList.focusableViewAvailable(mList); } }; /** * This method will be called when an item in the list is selected. * Subclasses should override. Subclasses can call * getListView().getItemAtPosition(position) if they need to access the * data associated with the selected item. * * @param l The ListView where the click happened * @param v The view that was clicked within the ListView * @param position The position of the view in the list * @param id The row id of the item that was clicked */ protected void onListItemClick(ListView l, View v, int position, long id) { } /** * Ensures the list view has been created before Activity restores all * of the view states. * *@see Activity#onRestoreInstanceState(Bundle) */ @Override protected void onRestoreInstanceState(Bundle state) { ensureList(); super.onRestoreInstanceState(state); } /** * @see Activity#onDestroy() */ @Override protected void onDestroy() { mHandler.removeCallbacks(mRequestFocus); super.onDestroy(); } /** * Updates the screen state (current list and other views) when the * content changes. * * @see Activity#onContentChanged() */ @Override public void onContentChanged() { super.onContentChanged(); View emptyView = findViewById(com.android.internal.R.id.empty); mList = (ListView) findViewById(com.android.internal.R.id.list); if (mList == null) { throw new RuntimeException( "Your content must have a ListView whose id attribute is " + "'android.R.id.list'"); } if (emptyView != null) { mList.setEmptyView(emptyView); } mList.setOnItemClickListener(mOnClickListener); if (mFinishedStart) { setListAdapter(mAdapter); } mHandler.post(mRequestFocus); mFinishedStart = true; } /** * Provide the cursor for the list view. */ public void setListAdapter(ListAdapter adapter) { synchronized (this) { ensureList(); mAdapter = adapter; mList.setAdapter(adapter); } } /** * Set the currently selected list item to the specified * position with the adapter's data * * @param position */ public void setSelection(int position) { mList.setSelection(position); } /** * Get the position of the currently selected list item. */ public int getSelectedItemPosition() { return mList.getSelectedItemPosition(); } /** * Get the cursor row ID of the currently selected list item. */ public long getSelectedItemId() { return mList.getSelectedItemId(); } /** * Get the activity's list view widget. */ public ListView getListView() { ensureList(); return mList; } /** * Get the ListAdapter associated with this activity's ListView. */ public ListAdapter getListAdapter() { return mAdapter; } private void ensureList() { if (mList != null) { return; } setContentView(com.android.internal.R.layout.list_content_simple); } private AdapterView.OnItemClickListener mOnClickListener = new AdapterView.OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { onListItemClick((ListView) parent, v, position, id); } }; }