我正在使用片段创建标签，我正在尝试将片段中的信息插入到我的数据库中。
所以我有3个RadioGroup，我在数据库中添加了用户标记的'Checked'单选按钮，我无法将数据添加到数据库中，因为出现以下错误：
尝试调用虚方法 “android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase（java.lang.String，int， android.database.sqlite.SQLiteDatabase $ CursorFactory， android.database.DatabaseErrorHandler）'对空对象引用
我使用的是DatabaseHandler函数（可以工作），例如
db.checkSetting（） - 检查数据库表是否为空，如果为空则返回false，如果不返回true。
db.updateSetting（） - 更新表中的数据。
db.addSetting（） - 使用新数据创建新表。
public class DatabaseHandler extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "database.db";
//table name
private static final String TABLE_DETAILS = "details";
private static final String TABLE_FOOD = "food";
private static final String TABLE_OLDDETAILS = "oldDetails";
private static final String TABLE_SETTING = "setting";
//Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_HEIGHT = "height";
private static final String KEY_WEIGHT = "weight";
private static final String KEY_CALORIES = "calories";
private static final String KEY_DATE = "date";
private static final String KEY_LEVEL = "level";
private static final String KEY_DURATION = "duration";
private static final String KEY_DAYS = "days";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_DETAILS_TABLE = "CREATE TABLE " + TABLE_DETAILS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_HEIGHT + " REAL," + KEY_WEIGHT + " REAL " + ")";
String CREATE_FOOD_TABLE = "CREATE TABLE " + TABLE_FOOD + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," + KEY_CALORIES + " INTEGER " + ")";
String CREATE_OLDDETAILS_TABLE = "CREATE TABLE " + TABLE_OLDDETAILS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_DATE + " TEXT," + KEY_HEIGHT + " REAL," + KEY_WEIGHT + " REAL " + ")";
String CREATE_SETTING_TABLE = "CREATE TABLE " + TABLE_SETTING + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_LEVEL + " INTEGER," + KEY_DURATION + " INTEGER," + KEY_DAYS + " INTEGER " + ")";
db.execSQL(CREATE_OLDDETAILS_TABLE);
db.execSQL(CREATE_DETAILS_TABLE);
db.execSQL(CREATE_FOOD_TABLE);
db.execSQL(CREATE_SETTING_TABLE);
}
// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_DETAILS);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_OLDDETAILS);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_FOOD);
db.execSQL("DROP TABLE IF EXISTS " + TABLE_SETTING);
// Create tables again
onCreate(db);
}
public boolean addSetting(int level, int duration, int days) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_ID, 1);
values.put(KEY_LEVEL, level);
values.put(KEY_DURATION, duration);
values.put(KEY_DAYS, days);
// Inserting Row
long result = db.insert(TABLE_SETTING, null, values);
if(result == -1){
return false;
}
else{
return true;
}
}
public boolean checkSetting(){
SQLiteDatabase db = this.getWritableDatabase();
String selectQuery = "SELECT * FROM " + TABLE_SETTING;
Cursor cursor = db.rawQuery(selectQuery, null);
Boolean rowExists;
if (cursor.moveToFirst())
{
// DO SOMETHING WITH CURSOR
rowExists = true;
} else
{
// I AM EMPTY
rowExists = false;
}
return rowExists;
}
public setting getSetting() {
String selectQuery = "SELECT * FROM " + TABLE_SETTING;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor != null)
cursor.moveToFirst();
setting set = new setting(cursor.getInt(1), cursor.getInt(2), cursor.getInt(3));
return set;
}
public int updateSetting(setting set) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_LEVEL, set.getLevel());
values.put(KEY_DURATION, set.getDuration());
values.put(KEY_DAYS, set.getDays());
Log.d("UPDATE: ", "updated all");
// updating row
return db.update(TABLE_SETTING, values, KEY_ID + " = ?", new String[] { String.valueOf(1) });
}
片段：
public class PageFragment extends Fragment {
DatabaseHandler db = new DatabaseHandler(getActivity()); //DATABASE
private int group1;
private int group2;
private int group3;
public static final String ARG_PAGE = "ARG_PAGE";
private int mPage;
public static PageFragment newInstance(int page) {
Bundle args = new Bundle();
args.putInt(ARG_PAGE, page);
PageFragment fragment = new PageFragment();
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mPage = getArguments().getInt(ARG_PAGE);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_training, container, false);
ViewStub stub = (ViewStub) view.findViewById(R.id.stub);
if(mPage == 1) { // mPage represents the ID of the tab/page/fragment that in use.
stub.setLayoutResource(R.layout.fragment_trainingone); // Sets resource for each fragment
View inflated = stub.inflate();
return inflated;
}
else{
stub.setLayoutResource(R.layout.fragment_trainingtwo);
View inflated = stub.inflate();
RadioGroup rg1 = (RadioGroup) inflated.findViewById(R.id.group1);
RadioGroup rg2 = (RadioGroup) inflated.findViewById(R.id.group2);
RadioGroup rg3 = (RadioGroup) inflated.findViewById(R.id.group3);
Button update = (Button) inflated.findViewById(R.id.update);
rg1.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
{
public void onCheckedChanged(RadioGroup group, int checkedId) {
switch(checkedId){
case R.id.radio1:
group1 = 1;
break;
case R.id.radio2:
group1 = 2;
break;
case R.id.radio3:
group1 = 3;
break;
}
}
});
rg2.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
{
public void onCheckedChanged(RadioGroup group, int checkedId) {
switch(checkedId){
case R.id.radio11:
group2 = 1;
break;
case R.id.radio22:
group2 = 2;
break;
case R.id.radio33:
group2 = 3;
break;
}
}
});
rg3.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
{
public void onCheckedChanged(RadioGroup group, int checkedId) {
switch(checkedId){
case R.id.radio111:
group3 = 1;
break;
case R.id.radio222:
group3 = 2;
break;
case R.id.radio333:
group3 = 3;
break;
}
}
});
update.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(android.view.View v) {
setting set = new setting(group1, group2, group3);
if (db.checkSetting()) {
db.updateSetting(set);
} else {
db.addSetting(group1, group2, group3);
}
}
});
return inflated;
}
}
}
如何在片段内将数据插入数据库并避免NullPointerException？
答案 0 :(得分：3)
你正在打电话
DatabaseHandler db = new DatabaseHandler(getActivity());
。在onCreate()或onAttach()方法中对其进行初始化，因此getActivity()不会返回null。
答案 1 :(得分：1)
尝试调用虚方法 “android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase（java.lang.String，int， android.database.sqlite.SQLiteDatabase $ CursorFactory， android.database.DatabaseErrorHandler）'对空对象引用
根据例外情况您必须在查询数据库之前打开数据库，请按照以下链接的帖子进行操作
public void openDataBase() throws SQLException
{
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}