当我点击打开我的乘法难度expandableList给出了这个错误
09-21 12:31:21.827 18918-18918/com.spizer.mizer2 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.spizer.mizer2, PID: 18918
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.spizer.mizer2.ExpandableListAdapter.getChildrenCount(ExpandableListAdapter.java:62)
at android.widget.ExpandableListConnector.refreshExpGroupMetadataList(ExpandableListConnector.java:563)
at android.widget.ExpandableListConnector.expandGroup(ExpandableListConnector.java:688)
at android.widget.ExpandableListView.handleItemClick(ExpandableListView.java:696)
at android.widget.ExpandableListView.performItemClick(ExpandableListView.java:656)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3667)
at android.widget.AbsListView$3.run(AbsListView.java:5590)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5972)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
在第62行，我不知道为什么但它没有为添加难度expandableList做这个，这里也是ExpandableListAdapter的类代码
package com.spizer.mizer2;
import java.util.HashMap;
import java.util.List;
import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;
public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context _context;
private List<String> _listDataHeader; // header titles
// child data in format of header title, child title
private HashMap<String, List<String>> _listDataChild;
public ExpandableListAdapter(Context context, List<String> listDataHeader,
HashMap<String, List<String>> listChildData) {
this._context = context;
this._listDataHeader = listDataHeader;
this._listDataChild = listChildData;
}
@Override
public Object getChild(int groupPosition, int childPosititon) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.get(childPosititon);
}
@Override
public long getChildId(int groupPosition, int childPosition) {
return childPosition;
}
@Override
public View getChildView(int groupPosition, final int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
final String childText = (String) getChild(groupPosition, childPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_item, null);
}
TextView txtListChild = (TextView) convertView
.findViewById(R.id.lblListItem);
txtListChild.setText(childText);
return convertView;
}
@Override
public int getChildrenCount(int groupPosition) {
return this._listDataChild.get(this._listDataHeader.get(groupPosition))
.size();
}
@Override
public Object getGroup(int groupPosition) {
return this._listDataHeader.get(groupPosition);
}
@Override
public int getGroupCount() {
return this._listDataHeader.size();
}
@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
@Override
public View getGroupView(int groupPosition, boolean isExpanded,
View convertView, ViewGroup parent) {
String headerTitle = (String) getGroup(groupPosition);
if (convertView == null) {
LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = infalInflater.inflate(R.layout.list_group, null);
}
TextView lblListHeader = (TextView) convertView
.findViewById(R.id.lblListHeader);
lblListHeader.setTypeface(null, Typeface.BOLD);
lblListHeader.setText(headerTitle);
return convertView;
}
@Override
public boolean hasStableIds() {
return false;
}
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
return true;
}
}
这里有其他类与此todo： DifficultyMenu.java
package com.spizer.mizer2;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.ExpandableListView;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import android.view.View;
import android.widget.ExpandableListView.OnChildClickListener;
import android.widget.ExpandableListView.OnGroupClickListener;
import android.widget.ExpandableListView.OnGroupCollapseListener;
import android.widget.ExpandableListView.OnGroupExpandListener;
import android.widget.Toast;
public class DifficultyMenu extends AppCompatActivity {
/** calls to make the class ProblemSelector usable in this class **/
final ProblemSelector PS = new ProblemSelector();
private int T1;
private int T2;
private int T3;
private int T4;
ExpandableListAdapter listAdapter;
ExpandableListView expListView;
List<String> listDataHeader;
HashMap<String, List<String>> listDataChild;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_difficulty_menu);
// here you'll retrieve the data sent...you can google how to do that.
// get the list view
expListView = (ExpandableListView) findViewById(R.id.lvExp);
// preparing list data
prepareListData();
listAdapter = new ExpandableListAdapter(this, listDataHeader, listDataChild);
// setting list adapter
expListView.setAdapter(listAdapter);
// List view Group click listener
expListView.setOnGroupClickListener(new OnGroupClickListener() {
@Override
public boolean onGroupClick(ExpandableListView parent, View v,
int groupPosition, long id) {
// Toast.makeText(getApplicationContext(),
// "Group Clicked " + listDataHeader.get(groupPosition),
// Toast.LENGTH_SHORT).show();
return false;
}
});
// List view Group expanded listener
expListView.setOnGroupExpandListener(new OnGroupExpandListener() {
@Override
public void onGroupExpand(int groupPosition) {
Toast.makeText(getApplicationContext(),
listDataHeader.get(groupPosition) + " Expanded",
Toast.LENGTH_SHORT).show();
}
});
// List view Group collapsed listener
expListView.setOnGroupCollapseListener(new OnGroupCollapseListener() {
@Override
public void onGroupCollapse(int groupPosition) {
Toast.makeText(getApplicationContext(),
listDataHeader.get(groupPosition) + " Collapsed",
Toast.LENGTH_SHORT).show();
}
});
// List view on child click listener
expListView.setOnChildClickListener(new OnChildClickListener() {
@Override
public boolean onChildClick(ExpandableListView parent, View v,
int groupPosition, int childPosition, long id) {
Toast.makeText(
getApplicationContext(),
listDataHeader.get(groupPosition)
+ " : "
+ listDataChild.get(listDataHeader.get(groupPosition)).get(childPosition), Toast.LENGTH_SHORT)
.show();
/** converts the selected number in the expandable list to a usable integer variable **/
if(listDataHeader.get(groupPosition).equals("AdditionDifficulty")) {
String St1 = listDataHeader.get(childPosition);
int AddDiff = Integer.parseInt(St1);
}
else if(listDataHeader.get(groupPosition).equals("SubtractionDifficulty")) {
String St2 = listDataHeader.get(childPosition);
int SubDiff = Integer.parseInt(St2);
}
else if(listDataHeader.get(groupPosition).equals("MultiplicationDifficulty")) {
String St3 = listDataHeader.get(childPosition);
int MultiDIff = Integer.parseInt(St3);
}
else if(listDataHeader.get(groupPosition).equals("DivisionDifficulty")) {
String St4 = listDataHeader.get(childPosition);
int DivisDiff = Integer.parseInt(St4);
}
// else {
// /** public static int e("DifficultyMenu.class", "could not parse a group position when user selected a field"); **/
// }
return false;
}
});
}
/*
* Preparing the list data
*/
private void prepareListData() {
listDataHeader = new ArrayList<>();
listDataChild = new HashMap<>();
// Adding child data
if(PS.AddProb) { listDataHeader.add("AdditionDifficulty"); }
if(PS.SubProb) { listDataHeader.add("SubtractionDifficulty"); }
if(PS.MultiProb) { listDataHeader.add("MultiplicationDifficulty"); }
if(PS.DivisProb) { listDataHeader.add("DivisionDifficulty"); }
// listDataHeader.add("AdditionDifficulty");
// listDataHeader.add("SubtractionDifficulty");
// listDataHeader.add("MultiplicationDifficulty");
// listDataHeader.add("DivisionDifficulty");
System.out.println(listDataHeader);
/** this removes fields that the user has not selected to practice **/
// if(!PS.AddProb) { listDataHeader.remove("AdditionDifficulty"); }
// if(!PS.SubProb) { listDataHeader.remove("SubtractionDifficulty"); }
// if(!PS.MultiProb) { listDataHeader.remove("MultiplicationDifficulty"); }
// if(!PS.DivisProb) { listDataHeader.remove("DivisionDifficulty"); }
// Adding child data
List<String> AdditionDifficulty = new ArrayList<>();
while (true) {
if (T1 < 21) {
String S1 = Integer.toString(T1);
AdditionDifficulty.add(S1);
T1++;
} else {
break;
}
}
List<String> SubtractionDifficulty = new ArrayList<>();
while (true) {
if (T2 < 21) {
String S2 = Integer.toString(T2);
SubtractionDifficulty.add(S2);
T2++;
} else {
break;
}
}
List<String> MultiplicationDifficulty = new ArrayList<>();
while (true) {
if (T3 < 21) {
String S3 = Integer.toString(T3);
MultiplicationDifficulty.add(S3);
T3++;
} else {
break;
}
}
List<String> DivisionDifficulty = new ArrayList<>();
while (true) {
if (T4 < 21) {
String S4 = Integer.toString(T4);
DivisionDifficulty.add(S4);
T4++;
} else {
break;
}
}
/** this draws out the Expandable lists **/
if(PS.AddProb) { listDataChild.put(listDataHeader.get(PS.ANum), AdditionDifficulty); } else {System.out.println("Something went wrong at line: 192"); Toast.makeText(getBaseContext(), "something went wrong: 192", Toast.LENGTH_SHORT).show();}
if(PS.SubProb) { listDataChild.put(listDataHeader.get(PS.SNum), SubtractionDifficulty); } else {System.out.println("Something went wrong at line: 193"); Toast.makeText(getBaseContext(), "something went wrong: 193", Toast.LENGTH_SHORT).show();}
if(PS.MultiProb) { listDataChild.put(listDataHeader.get(PS.MNum), MultiplicationDifficulty); } else {System.out.println("Something went wrong at line: 194"); Toast.makeText(getBaseContext(), "something went wrong: 194", Toast.LENGTH_SHORT).show();}
if(PS.DivisProb) { listDataChild.put(listDataHeader.get(PS.DNum), DivisionDifficulty); } else {System.out.println("Something went wrong at line: 195"); Toast.makeText(getBaseContext(), "something went wrong: 195", Toast.LENGTH_SHORT).show();}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_difficulty_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是最后一堂课：
package com.spizer.mizer2;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.Toast;
public class ProblemSelector extends AppCompatActivity {
public boolean AddProb = true;
public boolean SubProb = false;
public boolean MultiProb = true;
public boolean DivisProb = false;
public int ANum = 0;
public int SNum;
public int MNum;
public int DNum;
//ProblemSelector PS = new ProblemSelector();
CheckBox checkbox1, checkbox2, checkbox3, checkbox4;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_problem_selector);
checkbox1 = (CheckBox) findViewById(R.id.checkBox1);
checkbox2 = (CheckBox) findViewById(R.id.checkBox2);
checkbox3 = (CheckBox) findViewById(R.id.checkBox3);
checkbox4 = (CheckBox) findViewById(R.id.checkBox4);
/** waits for checkbox1 to be clicked then triggers the arguments below it **/
/** also sets the lists position if the other problems for training have been selected to practice **/
checkbox1.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (b) {
AddProb = true;
Toast.makeText(getBaseContext(), "Addition: True", Toast.LENGTH_SHORT).show();
System.out.println("Addition: True");
} else {
AddProb = false;
Toast.makeText(getBaseContext(), "Addition: False", Toast.LENGTH_SHORT).show();
System.out.println("Addition: False");
}
}
});
/** waits for checkbox2 to be clicked then triggers the arguments below it **/
/** also sets the lists position if the other problems for training have been selected to practice **/
checkbox2.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (b) {
SubProb = true;
Toast.makeText(getBaseContext(), "Subtraction: True", Toast.LENGTH_SHORT).show();
System.out.println("Subtraction: True");
if(AddProb == false) {
SNum = 0;
}
else if(AddProb == true) {
SNum = 1;
}
} else {
SubProb = false;
Toast.makeText(getBaseContext(), "Subtraction: False", Toast.LENGTH_SHORT).show();
System.out.println("Subtraction: False");
}
}
});
/** waits for checkbox3 to be clicked then triggers the arguments below it **/
/** also sets the lists position if the other problems for training have been selected to practice **/
checkbox3.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (b) {
MultiProb = true;
Toast.makeText(getBaseContext(), "Multiplication: True", Toast.LENGTH_SHORT).show();
System.out.println("Multiplication: True");
if(AddProb == false && SubProb == false) {
MNum = 0;
}
else if(AddProb == true && SubProb == false || AddProb == false && SubProb == true) {
MNum = 1;
}
else if(AddProb == true && SubProb == true) {
MNum = 2;
}
} else {
MultiProb = false;
Toast.makeText(getBaseContext(), "Multiplication: False", Toast.LENGTH_SHORT).show();
System.out.println("Multiplication: False");
}
}
});
/** waits for checkbox4 to be clicked then triggers the arguments below it **/
/** also sets the lists position if the other problems for training have been selected to practice **/
checkbox4.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (b) {
DivisProb = true;
Toast.makeText(getBaseContext(), "Division: True", Toast.LENGTH_SHORT).show();
System.out.println("Division: True");
if(AddProb == false && SubProb == false && MultiProb == false) {
DNum = 0;
}
else if(AddProb == true && SubProb == false && MultiProb == false || AddProb == false && SubProb == true && MultiProb == false || AddProb == false && SubProb == false && MultiProb == true) {
DNum = 1;
}
else if(AddProb == true && SubProb == true && MultiProb == false || AddProb == false && SubProb == true && MultiProb == true || AddProb == true && SubProb == false && MultiProb == true) {
DNum = 2;
}
else if(AddProb == true && SubProb == true && MultiProb == true) {
DNum = 3;
}
} else {
DivisProb = false;
Toast.makeText(getBaseContext(), "Division: False", Toast.LENGTH_SHORT).show();
System.out.println("Division: False");
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_problem_selector, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/** this is called when the user hits the continue button **/
public void DifficultyMenu(View view) {
Intent DifficultyView = new Intent(this, DifficultyMenu.class);
//DifficultyView.putExtra("addProb", PS.AddProb);
//DifficultyView.putExtra("subProb", PS.SubProb);
//DifficultyView.putExtra("multiProb", PS.MultiProb);
//DifficultyView.putExtra("divisProb", PS.DivisProb);
startActivity(DifficultyView);
}
}
答案 0 :(得分：0)
我能够通过使用此方法来解决我的问题
String St1 = listDataChild.get(listDataHeader.get(groupPosition)).get(childPosition);