将文件从片段保存到SQLite

Question

我与FragTest和Frag2有NewContact活动。我正在尝试获取FragTest中的字符串，并将其保存在我的数据库中。我的Frag2只是一个空视图。

LogCat

01-28 08:41:37.353: E/AndroidRuntime(1313): FATAL EXCEPTION: main
01-28 08:41:37.353: E/AndroidRuntime(1313): java.lang.NullPointerException
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at com.example.addressbookapp.DBHelper.insertContact(DBHelper.java:67)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at com.example.addressbookapp.FragTest$1.onClick(FragTest.java:46)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.view.View.performClick(View.java:4240)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.view.View$PerformClick.run(View.java:17721)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.os.Handler.handleCallback(Handler.java:730)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.os.Looper.loop(Looper.java:137)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at android.app.ActivityThread.main(ActivityThread.java:5103)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at java.lang.reflect.Method.invokeNative(Native Method)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at java.lang.reflect.Method.invoke(Method.java:525)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-28 08:41:37.353: E/AndroidRuntime(1313):     at dalvik.system.NativeStart.main(Native Method)

NewContact.java

public class NewContact extends FragmentActivity {
ViewPager viewPager = null;     
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_new_contact);
viewPager = (ViewPager)findViewById(R.id.pager);    
FragmentManager fragmentManager = getSupportFragmentManager();
viewPager.setAdapter(new MyAdapter(fragmentManager));   
viewPager.setOffscreenPageLimit(2);
}
public class MyAdapter extends FragmentStatePagerAdapter {  
public MyAdapter (FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int i) {
Fragment fragment = null;
if (i == 0)
{
fragment = new FragTest();
}
if (i == 1)
{
fragment = new Frag2();
}
return fragment;
}
@Override
public int getCount() {
return 2;
}   
}
}

FragTest.java

public class FragTest extends Fragment { 
EditText first_name, last_name, phone_number, email_address, home_address;
Button addNewContact;
DBHelper dbHelper = new DBHelper(getActivity());
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_test, container, false);    
first_name = (EditText) v.findViewById(R.id.firstName);
last_name = (EditText) v.findViewById(R.id.lastName);
phone_number = (EditText) v.findViewById(R.id.phoneNumber);
email_address = (EditText) v.findViewById(R.id.emailAddress);
home_address = (EditText) v.findViewById(R.id.homeAddress);
//save button
addNewContact = (Button) v.findViewById(R.id.saveButton);
addNewContact.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
HashMap<String, String> queryValuesMap = new HashMap<String, String>();
queryValuesMap.put("firstName", first_name.getText().toString());
queryValuesMap.put("lastName", last_name.getText().toString());
queryValuesMap.put("phoneNumber", phone_number.getText().toString());
queryValuesMap.put("emailAddress", email_address.getText().toString());
queryValuesMap.put("homeAddress", home_address.getText().toString());
dbHelper.insertContact(queryValuesMap);
}
});
return v;
}
}

DBHelper.java

public class DBHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "my_database.db";
private static final String TABLE_NAME = "my_table";
public static final String UID = "_id";
private static final String FIRST_NAME = "firstName";
private static final String LAST_NAME = "lastName";
private static final String PHONE_NUMBER = "phoneNumber";
private static final String EMAIL_ADDRESS = "emailAddress";
private static final String HOME_ADDRESS = "homeAddress";
private Context context;
// databaseVersion
private static final int DATABASE_VERSION = 18;
// database statements
private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME
+ " (" + UID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + FIRST_NAME
+ " VARCHAR (255), " + LAST_NAME + " VARCHAR (255), "
+ PHONE_NUMBER + " VARCHAR(255), " + EMAIL_ADDRESS
+ " VARCHAR (255), " + HOME_ADDRESS + " VARCHAR(255));";
private static final String DROP_TABLE = "DROP TABLE IF EXISTS "
+ TABLE_NAME;
public DBHelper(Context context) {
// context, database_name, cursorFactory, databaseVersion
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
Message.message(context, "onCreate called");
db.execSQL(CREATE_TABLE);
} catch (SQLException e) {
// TODO Auto-generated catch block
Message.message(context, "ERROR MESSAGE: " + e);
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
try {
Message.message(context, "onUpgrade called");
db.execSQL(DROP_TABLE);
onCreate(db);
} catch (SQLException e) {
// TODO Auto-generated catch block
Message.message(context, "ERROR MESSAGE: " + e);
}
}
public void insertContact(HashMap<String, String> queryValues) {
SQLiteDatabase sqdb = this.getWritableDatabase();
ContentValues ct_v = new ContentValues();
ct_v.put("firstName", queryValues.get("firstName"));
ct_v.put("lastName", queryValues.get("lastName"));
ct_v.put("phoneNumber", queryValues.get("phoneNumber"));
ct_v.put("emailAddress", queryValues.get("emailAddress"));
ct_v.put("homeAddress", queryValues.get("homeAddress"));
sqdb.insert(TABLE_NAME, null, ct_v);
sqdb.close();
}
public int updateContact(HashMap<String, String> queryValues) {
SQLiteDatabase sqdb = this.getWritableDatabase();
ContentValues ct_v = new ContentValues();
// update(contentValues): name of column, new value
ct_v.put("firstName", queryValues.get("firstName"));
ct_v.put("lastName", queryValues.get("lastName"));
ct_v.put("phoneNumber", queryValues.get("phoneNumber"));
ct_v.put("emailAddress", queryValues.get("emailAddress"));
ct_v.put("homeAddress", queryValues.get("homeAddress"));
return sqdb.update(TABLE_NAME, ct_v, UID + " =? ",
new String[] { queryValues.get("unique_id") });
}
public void deleteContact(String id) {
SQLiteDatabase sqdb = this.getWritableDatabase();
String deleteQuery = "DELETE FROM " + TABLE_NAME + " WHERE " + UID
+ " = '"+id+"';";
sqdb.execSQL(deleteQuery);
}
public ArrayList<HashMap<String, String>> getAllContacts() {
// contains every row of the database
ArrayList<HashMap<String, String>> contactArrayList = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT * FROM "+TABLE_NAME+" ORDER BY "+LAST_NAME+";";
SQLiteDatabase sqdb = this.getWritableDatabase();
Cursor cursor = sqdb.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
HashMap<String, String> contactMap = new HashMap<String, String>();
contactMap.put("unique_id", cursor.getString(0));
contactMap.put("firstName", cursor.getString(1));
contactMap.put("lastName", cursor.getString(2));
contactMap.put("phoneNumber", cursor.getString(3));
contactMap.put("emailAddress", cursor.getString(4));
contactMap.put("homeAddress", cursor.getString(5));
contactArrayList.add(contactMap);
} while (cursor.moveToNext());
}
return contactArrayList;
}
public HashMap<String, String> getContactInfo(String id) {
HashMap<String, String> contactMap = new HashMap<String, String>();
SQLiteDatabase sqdb = this.getReadableDatabase();
String selectQuery = "SELECT * FROM " + TABLE_NAME + " WHERE " + UID
+ "= '"+id+"';";
Cursor cursor = sqdb.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
contactMap.put("unique_id", cursor.getString(0));
contactMap.put("firstName", cursor.getString(1));
contactMap.put("lastName", cursor.getString(2));
contactMap.put("phoneNumber", cursor.getString(3));
contactMap.put("emailAddress", cursor.getString(4));
contactMap.put("homeAddress", cursor.getString(5));
} while (cursor.moveToNext());
}
return contactMap;
}
}

Answer 1

更换

DBHelper dbHelper = new DBHelper(getActivity()); 

至

DBHelper dbHelper = null; 

并将其初始化为onCreateView

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_test, container, false);
dbHelper = new DBHelper(getActivity()); // HERE IT IS
.....
}

Answer 2

您构建DBHelper太早了。此处传入的getActivity()Context为null:

DBHelper dbHelper = new DBHelper(getActivity());

将初始化推迟到例如onCreateView()，其中片段被附加到活动。