Android(安卓)ApiDemos示例解析(112):Views->Expandable Lists->1. Custom Adapter

Expandable List 与普通List的区别在于Expandable List可以显示两个层次，第一层称为”Group” 第二层为”Child” 。其中”Child”可以折叠或展开，有点像只支持两级的TreeView（文件浏览器）。

用法上和List 非常类似，下面的对应关系可以帮助理解Expandable List

ExpandableListActivity –>ListActivity
ExpandableListView –> ListView
ExpandableListAdapter –>ListAdapter

ExpandableListActivity 缺省的Layout 为一居中全屏显示的列表（两级）。Android也允许使用自定义的Layout来显示Expandable List. 为了使用自定义的Layout的，在XML中必须包括一个ExpandableListView对象且id必须为 @android:id/list。此外也可以为空列表定义一个View，此View的id为 @id/android:empty。

如下例为ExpandableListActivity 自定义一个Layout ,为在列表为空时显示“No Data”.可以在onCreate 使用setContentView设置这个自定义Layout .

<?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”>
<ExpandableListView android:id=”@id/android:list”
android:layout_width=”match_parent”
android:layout_height=”match_parent”
android:background=”#00FF00″
android:layout_weight=”1″
android:drawSelectorOnTop=”false”/>

ExpandableListActivity 调用setListAdapter(ExpandableListAdapter) 设置ExpandableListAdapter， ExpandableListAdapter 允许为”group” 和 “child”分别设置View。

例如本例 MyExpandableListAdapter 派生自BaseExpandableListAdapter，重载了getChildView 和getGroupView，分别为group 和child定义一个TextView，TextView的文本为Group名称或是Child的名称，分别对应在groups 和children。

// Sample data set. children[i] contains//the children (String[]) for groups[i].private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };private String[][] children = { { "Arnold", "Barry", "Chuck", "David" }, { "Ace", "Bandit", "Cha-Cha", "Deuce" }, { "Fluffy", "Snuggles" }, { "Goldy", "Bubbles" }};public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) { TextView textView = getGenericView(); textView.setText(getChild(groupPosition, childPosition).toString()); return textView;} public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { TextView textView = getGenericView(); textView.setText(getGroup(groupPosition).toString()); return textView;}

getExpandableListView() 取得当前Activity 对应的ExpandableListView，然后调用registerForContextMenu 为 ExpandableListView 添加Context Menu.

然后在onContextItemSelected事件中为List View 中的每个list Item 添加事件，本例使用Toast 显示一行文本，显示当前点击的事件。

public boolean onContextItemSelected(MenuItem item) { ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo(); String title = ((TextView) info.targetView).getText().toString(); int type = ExpandableListView.getPackedPositionType(info.packedPosition); if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) { int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition); Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos, Toast.LENGTH_SHORT).show(); return true; } else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) { int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show(); return true; } return false;}

Expandable Lists->1. Custom Adapter_第1张图片" class="aligncenter size-full wp-image-1902" style="border:1px solid black;">

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