An activity that displays an expandable list of items by binding to a data source implementing the ExpandableListAdapter, and exposes event handlers when the user selects an item.
ExpandableListActivity hosts a ExpandableListView object that can be bound to different data sources that provide a two-levels of data (the top-level is group, and below each group are children). Binding, screen layout, and row layout are discussed in the following sections.
Screen Layout
ExpandableListActivity has a default layout that consists of a single, full-screen, centered expandable list. 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 an ExpandableListView object with the id "@android:id/list" (or list if it's in code)
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:empty". Note that when an empty view is present, the expandable list view will be hidden when there is no data to display.
The following code demonstrates an (ugly) custom screen layout. It has a list with a green background, and an alternate red "no data" message.
<?xml version="1.0" encoding="UTF-8"?> <LinearLayout android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:paddingLeft="8" android:paddingRight="8"> <ExpandableListView id="android:list" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#00FF00" android:layout_weight="1" android:drawSelectorOnTop="false"/> <TextView id="android:empty" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#FF0000" android:text="No data"/> </LinearLayout>
Row Layout
The ExpandableListAdapter set in the ExpandableListActivity via setListAdapter(ExpandableListAdapter) provides the Views for each row. This adapter has separate methods for providing the group Views and child Views. There are a couple provided ExpandableListAdapters that simplify use of adapters: SimpleCursorTreeAdapter and SimpleExpandableListAdapter.With these, you can specify the layout of individual rows for groups and children in the list. These constructor takes a few parameters that specify layout resources for groups and children. It also has additional parameters that let you specify which data field to associate with which object in the row layout resource. The SimpleCursorTreeAdapter fetches data from Cursors and the SimpleExpandableListAdapter fetches data from Lists of Maps.
Android provides some standard row layout resources. These are in the 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.
<?xml version="1.0" encoding="utf-8"?> <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="vertical"> <TextView id="text1" android:textSize="16" android:textStyle="bold" android:layout_width="fill_parent" android:layout_height="wrap_content"/> <TextView id="text2" android:textSize="16" android:layout_width="fill_parent" android:layout_height="wrap_content"/> </LinearLayout>
You must identify the data bound to each TextView object in this layout. The syntax for this is discussed in the next section.
Binding to Data
You bind the ExpandableListActivity's ExpandableListView object to data using a class that implements the ExpandableListAdapter interface. Android provides two standard list adapters: SimpleExpandableListAdapter for static data (Maps), and SimpleCursorTreeAdapter for Cursor query results.
ExpandableListActivity() |
ExpandableListAdapter | getExpandableListAdapter() | |||||
Get the ExpandableListAdapter associated with this activity's ExpandableListView. | ||||||
ExpandableListView | getExpandableListView() | |||||
Get the activity's expandable list view widget. | ||||||
long | getSelectedId() | |||||
Gets the ID of the currently selected group or child. | ||||||
long | getSelectedPosition() | |||||
Gets the position (in packed position representation) of the currently selected group or child. | ||||||
boolean | onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) | |||||
Override this for receiving callbacks when a child has been clicked. | ||||||
void | onContentChanged() | |||||
Updates the screen state (current list and other views) when the content changes. | ||||||
void | onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) | |||||
Override this to populate the context menu when an item is long pressed. | ||||||
void | onGroupCollapse(int groupPosition) | |||||
Override this for receiving callbacks when a group has been collapsed. | ||||||
void | onGroupExpand(int groupPosition) | |||||
Override this for receiving callbacks when a group has been expanded. | ||||||
void | setListAdapter(ExpandableListAdapter adapter) | |||||
Provide the adapter for the expandable list. | ||||||
boolean | setSelectedChild(int groupPosition, int childPosition, boolean shouldExpandGroup) | |||||
Sets the selection to the specified child. | ||||||
void | setSelectedGroup(int groupPosition) | |||||
Sets the selection to the specified group. |
void | onRestoreInstanceState(Bundle state) | |||||
Ensures the expandable list view has been created before Activity restores all of the view states. |
Callback method to be invoked when a child in this expandable list has been clicked.
Called when a context menu for the view
is about to be shown.
Unlike onCreateOptionsMenu(Menu), this will be called every
time the context menu is about to be shown and should be populated for
the view (or item inside the view for AdapterView subclasses,
this can be found in the menuInfo
)).
Use onContextItemSelected(android.view.MenuItem) to know when an item has been selected.
It is not safe to hold onto the context menu after this method returns. Called when the context menu for this view is being built. It is not safe to hold onto the menu after this method returns.
groupPosition | The position of the group that contains the child. |
---|---|
childPosition | The position of the child within the group. |
shouldExpandGroup | Whether the child's group should be expanded if it is collapsed. |
groupPosition | The position of the group that should be selected. |
---|
state | the data most recently supplied in onSaveInstanceState(Bundle). |
---|
Copyright 2007 Google Inc. | Build 0.9_r1-98467 - 14 Aug 2008 18:48 |