我正在开发一个项目，其数据结构深度超过1级，我尝试将不同的用户定义数据类型设置为保存所有级别的信息。
第一级：一个只有一个LevelList为2级数据类型的类，以及一些访问所有级别数据的函数。
第二级：一个类，它有一些标准变量和一个Level3数据类型的ArrayList以及一些函数。
第三级：某些标准变量的类/记录
第一级数据类型的实例应该由我的应用程序的多个活动使用（几乎所有）。
这是我的问题：我可以初始化第一级并将一些对象添加到列表中，但我无法使用第二级。如果我在第二级列表中添加一些对象似乎都很好，但是当我访问此数据时，会发生NullPointerException。
这是我的问题：是否可以将数据类型设置为超过1级？我应该在哪里搜索错误。
为了更好地理解来源：
modulData.java（第一级）
package de.myApp.dataholder;
import java.util.ArrayList;
import android.util.Log;
public class modulData {
// Constructor
private static final modulData mainModulDataHolder = new modulData();
public static modulData getInstance() {return mainModulDataHolder;}
// Data
private ArrayList<isModulData> mIsModulData;
// Functions
public void init() {
this.mIsModulData = new ArrayList<isModulData>();
}
public isModulData getModul(int mID) {
isModulData result = null;
int i;
for (i = 0; i < mIsModulData.size(); i++) {
if (mIsModulData.get(i).ID() == mID) {
result = mIsModulData.get(i);
break;
}
}
return result;
}
public isCatData getCategory(int mID, int cID) {
isCatData result = new isCatData();
isCatData buffer = new isCatData();
int i,j ;
for (i = 0; i < mIsModulData.size(); i++) {
if (mIsModulData.get(i).ID() == mID) {
for(j = 0; j < mIsModulData.get(i).CountCategorys(); j++) {
buffer = mIsModulData.get(i).getCategory(j);
if (buffer.ID() == cID) {
result = buffer;
break;
}
}
}
}
return result;
}
public int ModulCount() {
int result = 0;
if (mIsModulData != null) { result = mIsModulData.size(); }
return result;
}
public int CategoryCount(int mID) {
int result = -1;
int i;
for (i = 0; i < mIsModulData.size(); i++) {
if (mIsModulData.get(i).ID() == mID) {
result = mIsModulData.get(i).CountCategorys();
break;
}
}
return result;
}
public int addModulWithJSON(String jsonString) {
int result = -1;
isModulData newModul = new isModulData();
newModul.initCategorys();
if (mIsModulData == null) { this.init(); }
result = newModul.decodeFromJSON(jsonString);
mIsModulData.add(newModul);
return result;
}
public int addCategoryWithJSON(int mID, String jsonString) {
int result = -1;
int i;
for (i = 0; i < mIsModulData.size(); i++){
if (mIsModulData.get(i).ID() == mID) {
result = mIsModulData.get(i).addCategoryWithJSON(jsonString);
Log.i("AddCategoryWithJSON","Add Category "+ String.valueOf(result));
// Here is the Problem: Added but no access to Data. Null Object reference !!!!
Log.i("AddCategoryWithJSON", mIsModulData.get(mID).getCategory(result).Title());
break;
}
}
return result;
}
}
isModulData.java（第二级）
package de.myApp.dataholder;
import java.util.ArrayList;
import org.json.JSONArray;
import org.json.JSONException;
import android.util.Log;
public class isModulData {
// Constructor
private static final isModulData modulDataHolder = new isModulData();
public static isModulData getInstance() {return modulDataHolder;}
// Data
private ArrayList<isCatData> mIsCatData;
private int mID;
private String mTitle;
private boolean misActive;
private int mBackgroundID;
// Functions
public int ID() { return this.mID; }
public String Title() { return this.mTitle; }
public boolean ActiveState() { return this.misActive; }
public int BackgroundID() { return this.mBackgroundID; }
public int decodeFromJSON(String jsonString) {
int result;
try {
JSONArray jArray = new JSONArray(jsonString);
this.mID = Integer.parseInt(jArray.getString(0).toString());
this.mTitle = jArray.getString(1).toString();
this.misActive = Boolean.parseBoolean(jArray.getString(2).toString());
this.mBackgroundID = Integer.parseInt(jArray.getString(3).toString());
result = this.mID;
} catch (JSONException e) {
e.printStackTrace();
Log.w("JSONDecode CMD801","Decode raised in JSONException ["+e.toString()+"]");
result = -1;
}
return result;
}
public int addCategoryWithJSON(String jsonString) {
int result = -1;
if (this.mIsCatData == null) { this.initCategorys(); }
isCatData cNewCategory = new isCatData();
result = cNewCategory.decodeFromJSON(jsonString);
this.mIsCatData.add(cNewCategory);
return result;
}
public isCatData getCategory(int cID) {
isCatData result = new isCatData();
if (cID < mIsCatData.size() -1) {
result = mIsCatData.get(cID);
} else {
result = null;
}
return result;
}
public void initCategorys() {
this.mIsCatData = new ArrayList<isCatData>();
}
public int CountCategorys() {
return this.mIsCatData.size();
}
}
isCatData.java（第三级）
package de.myApp.dataholder;
import org.json.JSONArray;
import org.json.JSONException;
import android.util.Log;
public class isCatData {
// Constructor
private static final isCatData catDataHolder = new isCatData();
public static isCatData getInstance() {return catDataHolder;}
// Data
private int cID;
private String cTitle;
private boolean cisActive;
private boolean cisWriteEnable;
private int cBackgroundID;
// Functions
public int ID() { return this.cID; }
public String Title() { return this.cTitle; }
public boolean ActiveState() { return this.cisActive; }
public boolean WriteEnableState() { return this.cisWriteEnable; }
public int BackgroundID() { return this.cBackgroundID; }
public int decodeFromJSON(String jsonString) {
int result;
try {
JSONArray jArray = new JSONArray(jsonString);
this.cID = Integer.parseInt(jArray.getString(0).toString());
this.cTitle = jArray.getString(1).toString();
this.cisActive = Boolean.parseBoolean(jArray.getString(2).toString());
this.cisWriteEnable = Boolean.parseBoolean(jArray.getString(3).toString());
this.cBackgroundID = Integer.parseInt(jArray.getString(4).toString());
result = this.cID;
} catch (JSONException e) {
e.printStackTrace();
Log.w("JSONDecode CMD801","Decode raised in JSONException ["+e.toString()+"]");
result = -1;
}
return result;
}
}