一般來說在Android里要實現樹形菜單，都是用ExpandableList(也有高手自己繼承ListView或者LinearLayout來做)，但是ExpandableList一般只能實現2級樹形菜單。本文所述實例也依然使用ExpandableList，但是要實現的是3級樹形菜單。
本文程序運行效果圖如下圖所示：
當用BaseExpandableListAdapter來實現二級樹形菜單時，父項(getGroupView())和子項(getChildView())都是使用TextView。當要實現三級樹形菜單時，子項(getChildView())就必須使用ExpandableList了。另外還要定義結構體來方便調用三級樹形的數據，二級樹形菜單可以用如下：
static public class TreeNode{ Object parent; List<Object> childs=new ArrayList<Object>();}三級樹形菜單可以用如下，子項是二級樹形菜單的結構體如下所示：
static public class SuperTreeNode { Object parent; //二級樹形菜單的結構體 List<TreeViewAdapter.TreeNode> childs = new ArrayList<TreeViewAdapter.TreeNode>();}實現三級樹形菜單有兩點要注意的：
1、第二級也是個樹形菜單，因此必須在第二級項目展開/回收時設置足夠的空間來完全顯示二級樹形菜單；
2、在實現三級樹形菜單時，發現菜單的方法都是用不了(如OnChildClickListener、OnGroupClickListener等)，因此要獲得選中的數據就必須在外部定義好回調函數，然后在第二級生成二級樹形菜單時回調這個外部函數。
此外還需要注意：本文在解決No.2關鍵點的時候，只能取得第三級選中的序號。而第一，第二級依然無法獲取其序號。
main.xml源碼如下：
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <LinearLayout android:id="@+id/LinearLayout01" android:layout_width="wrap_content" android:layout_height="wrap_content"> <Button android:layout_height="wrap_content" android:text="兩層結構" android:layout_width="160dip" android:id="@+id/btnNormal"></Button> <Button android:layout_height="wrap_content" android:text="三層結構" android:layout_width="160dip" android:id="@+id/btnSuper"></Button> </LinearLayout> <ExpandableListView android:id="@+id/ExpandableListView01" android:layout_width="fill_parent" android:layout_height="fill_parent"></ExpandableListView></LinearLayout>
testExpandableList.java是主類，調用其他工具類，源碼如下：
package com.testExpandableList;import java.util.List;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.ExpandableListView;import android.widget.ExpandableListView.OnChildClickListener;import android.widget.Toast;public class testExpandableList extends Activity { /** Called when the activity is first created. */ ExpandableListView expandableList; TreeViewAdapter adapter; SuperTreeViewAdapter superAdapter; Button btnNormal,btnSuper; // Sample data set. children[i] contains the children (String[]) for groups[i]. public String[] groups = { "xxxx好友", "xxxx同學", "xxxxx女人"}; public String[][] child= { { "A君", "B君", "C君", "D君" }, { "同學甲", "同學乙", "同學丙"}, { "御姐", "蘿莉" } }; public String[] parent = { "xxxx好友", "xxxx同學"}; public String[][][] child_grandson= { {{"A君"}, {"AA","AAA"}}, {{"B君"}, {"BBB","BBBB","BBBBB"}}, {{"C君"}, {"CCC","CCCC"}}, {{"D君"}, {"DDD","DDDD","DDDDD"}}, }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); this.setTitle("ExpandableListView練習----hellogv"); btnNormal=(Button)this.findViewById(R.id.btnNormal); btnNormal.setOnClickListener(new ClickEvent()); btnSuper=(Button)this.findViewById(R.id.btnSuper); btnSuper.setOnClickListener(new ClickEvent()); adapter=new TreeViewAdapter(this,TreeViewAdapter.PaddingLeft>>1); superAdapter=new SuperTreeViewAdapter(this,stvClickEvent); expandableList=(ExpandableListView) testExpandableList.this.findViewById(R.id.ExpandableListView01); } class ClickEvent implements View.OnClickListener{ @Override public void onClick(View v) { adapter.RemoveAll(); adapter.notifyDataSetChanged(); superAdapter.RemoveAll(); superAdapter.notifyDataSetChanged(); if(v==btnNormal) { List<TreeViewAdapter.TreeNode> treeNode = adapter.GetTreeNode(); for(int i=0;i<groups.length;i++) { TreeViewAdapter.TreeNode node=new TreeViewAdapter.TreeNode(); node.parent=groups[i]; for(int ii=0;ii<child[i].length;ii++) { node.childs.add(child[i][ii]); } treeNode.add(node); } adapter.UpdateTreeNode(treeNode); expandableList.setAdapter(adapter); expandableList.setOnChildClickListener(new OnChildClickListener(){ @Override public boolean onChildClick(ExpandableListView arg0, View arg1, int parent, int children, long arg4) { String str="parent id:"+String.valueOf(parent)+",children id:"+String.valueOf(children); Toast.makeText(testExpandableList.this, str, 300).show(); return false; } }); } else if(v==btnSuper){ List<SuperTreeViewAdapter.SuperTreeNode> superTreeNode = superAdapter.GetTreeNode(); for(int i=0;i<parent.length;i++)//第一層 { SuperTreeViewAdapter.SuperTreeNode superNode=new SuperTreeViewAdapter.SuperTreeNode(); superNode.parent=parent[i]; //第二層 for(int ii=0;ii<child_grandson.length;ii++) { TreeViewAdapter.TreeNode node=new TreeViewAdapter.TreeNode(); node.parent=child_grandson[ii][0][0];//第二級菜單的標題 for(int iii=0;iii<child_grandson[ii][1].length;iii++)//第三級菜單 { node.childs.add(child_grandson[ii][1][iii]); } superNode.childs.add(node); } superTreeNode.add(superNode); } superAdapter.UpdateTreeNode(superTreeNode); expandableList.setAdapter(superAdapter); } } } /** * 三級樹形菜單的事件不再可用，本函數由三級樹形菜單的子項（二級菜單）進行回調 */ OnChildClickListener stvClickEvent=new OnChildClickListener(){ @Override public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) { String str="parent id:"+String.valueOf(groupPosition)+",children id:"+String.valueOf(childPosition); Toast.makeText(testExpandableList.this, str, 300).show(); return false; } };}TreeViewAdapter.java是實現二級樹形菜單的工具類，源碼如下：
package com.testExpandableList;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.util.Log;import android.view.Gravity;import android.view.View;import android.view.ViewGroup;import android.widget.AbsListView;import android.widget.BaseExpandableListAdapter;import android.widget.TextView;public class TreeViewAdapter extends BaseExpandableListAdapter{ public static final int ItemHeight=48;//每項的高度 public static final int PaddingLeft=36;//每項的高度 private int myPaddingLeft=0;//如果是由SuperTreeView調用，則作為子項需要往右移 static public class TreeNode{ Object parent; List<Object> childs=new ArrayList<Object>(); } List<TreeNode> treeNodes = new ArrayList<TreeNode>(); Context parentContext; public TreeViewAdapter(Context view,int myPaddingLeft) { parentContext=view; this.myPaddingLeft=myPaddingLeft; } public List<TreeNode> GetTreeNode() { return treeNodes; } public void UpdateTreeNode(List<TreeNode> nodes) { treeNodes=nodes; } public void RemoveAll() { treeNodes.clear(); } public Object getChild(int groupPosition, int childPosition) { return treeNodes.get(groupPosition).childs.get(childPosition); } public int getChildrenCount(int groupPosition) { return treeNodes.get(groupPosition).childs.size(); } static public TextView getTextView(Context context) { AbsListView.LayoutParams lp = new AbsListView.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, ItemHeight); TextView textView = new TextView(context); textView.setLayoutParams(lp); textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT); return textView; } public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) { TextView textView = getTextView(this.parentContext); textView.setText(getChild(groupPosition, childPosition).toString()); textView.setPadding(myPaddingLeft+PaddingLeft, 0, 0, 0); return textView; } public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { TextView textView = getTextView(this.parentContext); textView.setText(getGroup(groupPosition).toString()); textView.setPadding(myPaddingLeft+(PaddingLeft>>1), 0, 0, 0); return textView; } public long getChildId(int groupPosition, int childPosition) { return childPosition; } public Object getGroup(int groupPosition) { return treeNodes.get(groupPosition).parent; } public int getGroupCount() { return treeNodes.size(); } public long getGroupId(int groupPosition) { return groupPosition; } public boolean isChildSelectable(int groupPosition, int childPosition) { return true; } public boolean hasStableIds() { return true; }}SuperTreeViewAdapter.java是實現三級樹形菜單的工具類，會用到TreeViewAdapter.java，源碼如下：
package com.testExpandableList;import java.util.ArrayList;import java.util.List;import com.testExpandableList.TreeViewAdapter.TreeNode;import android.content.Context;import android.view.View;import android.view.ViewGroup;import android.widget.AbsListView;import android.widget.BaseExpandableListAdapter;import android.widget.ExpandableListView;import android.widget.ExpandableListView.OnChildClickListener;import android.widget.ExpandableListView.OnGroupCollapseListener;import android.widget.ExpandableListView.OnGroupExpandListener;import android.widget.TextView;public class SuperTreeViewAdapter extends BaseExpandableListAdapter { static public class SuperTreeNode { Object parent; //二級樹形菜單的結構體 List<TreeViewAdapter.TreeNode> childs = new ArrayList<TreeViewAdapter.TreeNode>(); } private List<SuperTreeNode> superTreeNodes = new ArrayList<SuperTreeNode>(); private Context parentContext; private OnChildClickListener stvClickEvent;//外部回調函數 public SuperTreeViewAdapter(Context view,OnChildClickListener stvClickEvent) { parentContext = view; this.stvClickEvent=stvClickEvent; } public List<SuperTreeNode> GetTreeNode() { return superTreeNodes; } public void UpdateTreeNode(List<SuperTreeNode> node) { superTreeNodes = node; } public void RemoveAll() { superTreeNodes.clear(); } public Object getChild(int groupPosition, int childPosition) { return superTreeNodes.get(groupPosition).childs.get(childPosition); } public int getChildrenCount(int groupPosition) { return superTreeNodes.get(groupPosition).childs.size(); } public ExpandableListView getExpandableListView() { AbsListView.LayoutParams lp = new AbsListView.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, TreeViewAdapter.ItemHeight); ExpandableListView superTreeView = new ExpandableListView(parentContext); superTreeView.setLayoutParams(lp); return superTreeView; } /** * 三層樹結構中的第二層是一個ExpandableListView */ public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) { // 是 final ExpandableListView treeView = getExpandableListView(); final TreeViewAdapter treeViewAdapter = new TreeViewAdapter(this.parentContext,0); List<TreeNode> tmp = treeViewAdapter.GetTreeNode();//臨時變量取得TreeViewAdapter的TreeNode集合，可為空 final TreeNode treeNode=(TreeNode) getChild(groupPosition, childPosition); tmp.add(treeNode); treeViewAdapter.UpdateTreeNode(tmp); treeView.setAdapter(treeViewAdapter); //關鍵點：取得選中的二級樹形菜單的父子節點,結果返回給外部回調函數 treeView.setOnChildClickListener(this.stvClickEvent); /** * 關鍵點：第二級菜單展開時通過取得節點數來設置第三級菜單的大小 */ treeView.setOnGroupExpandListener(new OnGroupExpandListener() { @Override public void onGroupExpand(int groupPosition) { AbsListView.LayoutParams lp = new AbsListView.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, (treeNode.childs.size()+1)*TreeViewAdapter.ItemHeight + 10); treeView.setLayoutParams(lp); } }); /** * 第二級菜單回收時設置為標準Item大小 */ treeView.setOnGroupCollapseListener(new OnGroupCollapseListener() { @Override public void onGroupCollapse(int groupPosition) { AbsListView.LayoutParams lp = new AbsListView.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT, TreeViewAdapter.ItemHeight); treeView.setLayoutParams(lp); } }); treeView.setPadding(TreeViewAdapter.PaddingLeft, 0, 0, 0); return treeView; } /** * 三級樹結構中的首層是TextView,用于作為title */ public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { TextView textView = TreeViewAdapter.getTextView(this.parentContext); textView.setText(getGroup(groupPosition).toString()); textView.setPadding(TreeViewAdapter.PaddingLeft, 0, 0, 0); return textView; } public long getChildId(int groupPosition, int childPosition) { return childPosition; } public Object getGroup(int groupPosition) { return superTreeNodes.get(groupPosition).parent; } public int getGroupCount() { return superTreeNodes.size(); } public long getGroupId(int groupPosition) { return groupPosition; } public boolean isChildSelectable(int groupPosition, int childPosition) { return true; } public boolean hasStableIds() { return true; }}總結，使用ExpandableList實現三級樹形菜單時有些bug不好解決，而且定義三維數組的時候也要倍加小心！所以盡量把數據化簡來使用二級樹形菜單。
希望本文所述代碼對大家進行Android程序設計有一定的幫助。
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