我已经尝试修复这两个错误有一段时间了，我觉得这与我对打开新 Activity 时发生的情况存在根本性误解有关。基本上该程序是一个任务管理程序。当我添加新任务而不修改类别时，它工作得很好，并且当我添加新任务以显示这些新任务时，数据库更新正常，应用程序的主页更新。
但是，我最近添加了“添加类别”按钮的功能。此按钮的目的是打开一个新的列表 Activity ，允许用户添加新的任务类别。每次我从任务编辑 Activity 中打开它，然后按后退按钮返回主页时，数据库中的所有任务都会被清除。想知道是否有人可以告诉我发生了什么事以及为什么数据被删除。
这是首页的相关代码 fragment (显示所有任务的 ListView :
private RemindersDbAdapter mDbHelper;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.reminder_list);
mDbHelper = new RemindersDbAdapter(this);
mDbHelper.open();
fillData();
registerForContextMenu(getListView());
}
private void fillData() {
Cursor remindersCursor = mDbHelper.fetchAllReminders();
startManagingCursor(remindersCursor);
// Create an array to specify the fields we want to display in the list (only TITLE)
String[] from = new String[]{RemindersDbAdapter.KEY_TITLE};
// and an array of the fields we want to bind those fields to (in this case just text1)
int[] to = new int[]{R.id.text1};
// Now create a simple cursor adapter and set it to display
SimpleCursorAdapter reminders =
new SimpleCursorAdapter(this, R.layout.reminder_row, remindersCursor, from, to);
setListAdapter(reminders);
}
以下是我的任务编辑 View 的一些代码(调用类别列表 Activity 的代码):
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mDbHelper = new RemindersDbAdapter(this);
//mCatDbHelper = new CategoriesDbAdapter(this);
setContentView(R.layout.reminder_edit);
mCalendar = Calendar.getInstance();
mTitleText = (EditText) findViewById(R.id.title);
//mBodyText = (EditText) findViewById(R.id.body);
mDateButton = (Button) findViewById(R.id.reminder_date);
mTimeButton = (Button) findViewById(R.id.reminder_time);
mLowPriorityButton = (Button) findViewById(R.id.low_priority);
mMedPriorityButton = (Button) findViewById(R.id.med_priority);
mHighPriorityButton = (Button) findViewById(R.id.high_priority);
mManageCategories = (Button) findViewById(R.id.manage_categories);
mSchoolRadio = (RadioButton)findViewById(R.id.radio_schoolwork);
mFamilyRadio = (RadioButton)findViewById(R.id.radio_family);
mOtherRadio = (RadioButton)findViewById(R.id.radio_other);
mContext = this;
priority = "Low";
category = "Other";
mConfirmButton = (Button) findViewById(R.id.confirm);
mRowId = savedInstanceState != null ? savedInstanceState.getLong(RemindersDbAdapter.KEY_ROWID)
: -1L;
registerButtonListenersAndSetDefaultText();
}
private void setRowIdFromIntent() {
if (mRowId == -1L) {
Bundle extras = getIntent().getExtras();
mRowId = extras != null ? extras.getLong(RemindersDbAdapter.KEY_ROWID)
: -1L;
}
}
@Override
protected void onPause() {
super.onPause();
mDbHelper.close();
}
@Override
protected void onResume() {
super.onResume();
mDbHelper.open();
setRowIdFromIntent();
//if(mRowId != -1L)
populateFields();
}
@Override
protected Dialog onCreateDialog(int id) {
switch(id) {
case DATE_PICKER_DIALOG:
return showDatePicker();
case TIME_PICKER_DIALOG:
return showTimePicker();
}
return super.onCreateDialog(id);
}
private void populateFields() {
// Only populate the text boxes and change the calendar date
// if the row is not null from the database.
if (mRowId != -1L) {
Cursor reminder = mDbHelper.fetchReminder(mRowId);
startManagingCursor(reminder);
mTitleText.setText(reminder.getString(
reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_TITLE)));
category = reminder.getString(reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_CATEGORY));
if(category.equals("School"))
mSchoolRadio.setChecked(true);
else if(category.equals("Family"))
mFamilyRadio.setChecked(true);
else
mOtherRadio.setChecked(true);
// Get the date from the database and format it for our use.
SimpleDateFormat dateTimeFormat = new SimpleDateFormat(DATE_TIME_FORMAT);
Date date = null;
try {
String dateString = reminder.getString(reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_DATE_TIME));
date = dateTimeFormat.parse(dateString);
mCalendar.setTime(date);
} catch (ParseException e) {
Log.e("ReminderEditActivity", e.getMessage(), e);
}
} else {
// This is a new task - add defaults from preferences if set.
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
String defaultTitleKey = getString(R.string.pref_task_title_key);
String defaultTimeKey = getString(R.string.pref_default_time_from_now_key);
String defaultTitle = prefs.getString(defaultTitleKey, null);
String defaultTime = prefs.getString(defaultTimeKey, null);
if(defaultTitle != null)
mTitleText.setText(defaultTitle);
if(defaultTime != null)
mCalendar.add(Calendar.MINUTE, Integer.parseInt(defaultTime));
}
updateDateButtonText();
updateTimeButtonText();
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if(mRowId == -1L)
mRowId = -1L;
outState.putLong(RemindersDbAdapter.KEY_ROWID, mRowId);
}
/*
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
mRowId = savedInstanceState != null ? savedInstanceState.getLong(RemindersDbAdapter.KEY_ROWID)
: -1L;
}
*/
private void saveState() {
String title = mTitleText.getText().toString();
//String body = mBodyText.getText().toString();
SimpleDateFormat dateTimeFormat = new SimpleDateFormat(DATE_TIME_FORMAT);
String reminderDateTime = dateTimeFormat.format(mCalendar.getTime());
if (mRowId == -1L) {
long id = mDbHelper.createReminder(title, priority, category, reminderDateTime);
if (id > 0) {
mRowId = id;
}
} else {
mDbHelper.updateReminder(mRowId, title, priority, category, reminderDateTime);
}
new ReminderManager(this).setReminder(mRowId, mCalendar);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
super.onActivityResult(requestCode, resultCode, intent);
}
以下是对导致问题的新 CategoryListActivity Activity 的调用(与上述代码在同一类中):
mManageCategories.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i = new Intent(mContext, CategoryListActivity.class);
startActivity(i);
//populateFields();
}
});
我遗漏了很多不太相关的代码。无论如何，就像我上面所说的那样......主要问题是，一旦我启动这个新的 CategoryListActivity Activity ，数据库和所有任务都会被清除。奇怪的是，即使我重新启动模拟器，只要我不启动 CategoryListActivity，任务就不会被删除。如果有人知道发生了什么事，请帮忙。
最佳答案
Andrew 查看这两个链接，它们将向您解释有关数据库集成的所有内容。
http://www.devx.com/wireless/Article/40842/1954
http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/
关于java - 每次我打开新 Activity 时，Android SQLite 数据库似乎都会被清除，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7857624/