问题描述
我发现这个 multilevel expandable listview 对我的项目非常准确,但我还想为每第三个级别(这是视图的最后一层)子项添加一个不同的 toast。我试过这个:
expandableListView.setonChildClickListener(new ExpandableListView.OnChildClickListener() {
@Override
public boolean onChildClick(ExpandableListView parent,View v,int groupPosition,int childPosition,long id) {
Toast.makeText(thirdLevelq1.put(q1[0] this,"The first child",Toast.LENGTH_LONG).show();
return false;
}
});
但它给出了错误。我什至尝试对每个 childItem 使用相同的 toast 文本,应用程序安装但当我打开适配器时崩溃。那么,如何正确添加它们?
Java:
package com.bacon.expandablelistview;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ExpandableListView expandableListView;
String[] parent = new String[]{"What is View?","What is Layout?","What is Dynamic Views?"};
String[] q1 = new String[]{"List View","Grid View"};
String[] q2 = new String[]{"Linear Layout","Relative Layout"};
String[] q3 = new String[]{"Recycle View"};
String[] des1 = new String[]{"A layout that organizes its children into a single horizontal or vertical row. It creates a scrollbar if the length of the window exceeds the length of the screen."};
String[] des2 = new String[]{"Enables you to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent)."};
String[] des3 = new String[]{"This list contains linear layout information"};
String[] des4 = new String[]{"This list contains relative layout information,displays a scrolling grid of columns and rows"};
String[] des5 = new String[]{"Under the RecyclerView model,several different components work together to display your data. Some of these components can be used in their unmodified form; for example,your app is likely to use the RecyclerView class directly. In other cases,we provide an abstract class,and your app is expected to extend it; for example,every app that uses RecyclerView needs to define its own view holder,which it does by extending the abstract RecyclerView.ViewHolder class."};
LinkedHashMap<String,String[]> thirdLevelq1 = new LinkedHashMap<>();
LinkedHashMap<String,String[]> thirdLevelq2 = new LinkedHashMap<>();
LinkedHashMap<String,String[]> thirdLevelq3 = new LinkedHashMap<>();
/**
* Second level array list
*/
List<String[]> secondLevel = new ArrayList<>();
/**
* Inner level data
*/
List<LinkedHashMap<String,String[]>> data = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//The problem starts here
expandableListView.setonChildClickListener(new ExpandableListView.OnChildClickListener() {
@Override
public boolean onChildClick(ExpandableListView parent,long id) {
Toast.makeText(getApplicationContext(),Toast.LENGTH_LONG).show();
return false;
}
});
setUpAdapter();
}
private void setUpAdapter() {
secondLevel.add(q1);
secondLevel.add(q2);
secondLevel.add(q3);
thirdLevelq1.put(q1[0],des1);
thirdLevelq1.put(q1[1],des2);
thirdLevelq2.put(q2[0],des3);
thirdLevelq2.put(q2[1],des4);
thirdLevelq3.put(q3[0],des5);
data.add(thirdLevelq1);
data.add(thirdLevelq2);
data.add(thirdLevelq3);
expandableListView = (ExpandableListView) findViewById(R.id.expandible_listview);
//passing three level of information to constructor
ThreeLevellistadapter threeLevellistadapterAdapter = new ThreeLevellistadapter(this,parent,secondLevel,data);
expandableListView.setAdapter(threeLevellistadapterAdapter);
expandableListView.setonGroupExpandListener(new ExpandableListView.OnGroupExpandListener() {
int prevIoUsGroup = -1;
@Override
public void onGroupExpand(int groupPosition) {
if (groupPosition != prevIoUsGroup)
expandableListView.collapseGroup(prevIoUsGroup);
prevIoUsGroup = groupPosition;
}
});
}
}
提前致谢。
编辑:当我使用 Toast.makeText(getApplicationContext(),Toast.LENGTH_LONG).show();
时,它的崩溃日志说:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ExpandableListView.setonChildClickListener(android.widget.ExpandableListView$OnChildClickListener)' on a null object reference
解决方法
请在 expandableListView.setOnChildClickListener
初始化后设置此侦听器 expandableListView
,即在您的情况下 setUpAdapter()
之后,因为当您尝试设置侦听器时 expandableListView
仍然为空因为你的初始化是在之后。
这就是 NullPointerException
的原因。因为设置监听器时 expandableListView
为空。
干杯
,@Override
public void onFinalChildClick(int plpos,int slpos,int tlpos) {
String msg = "";
switch (tlpos) {
case 0:
msg = "Shakespear is a good poet";
break;
case 1:
msg = "Earth isn't flat";
break;
default:
msg = "Unknown";
}
Toast.makeText(this,msg,Toast.LENGTH_SHORT).show();
}
@Override
public void onFinalItemClick(String plItem,String slItem,String tlItem) {
String inMsg = plItem + "," + slItem + "," + tlItem;
String outMsg = "";
if (inMsg.equals("group 1,Child Level 1,A")){
outMsg = "Shakespear is a good poet";
} else if (inMsg.equals("group 1,B")){
outMsg = "Earth isn't flat";
} else {
outMsg = "Unknown";
}
Toast.makeText(this,outMsg,Toast.LENGTH_SHORT).show();
}