我有一个DatabaseConnector类，我想检查数据库是否为空，然后显示警告，点击它将关闭活动。
这是我的DatabaseConnector类
public class DatabaseConnector {
// Declare Variables
private static final String DB_NAME = "MyNotes";
private static final String TABLE_NAME = "tablenotes";
private static final String TITLE = "title";
private static final String ID = "_id";
private static final String NOTE = "note";
private static final int DATABASE_VERSION = 2;
private SQLiteDatabase database;
private DatabaseHelper dbOpenHelper;
public static final String MAINCAT = "maincat";
public static final String SUBCAT = "subcat";
public DatabaseConnector(Context context) {
dbOpenHelper = new DatabaseHelper(context, DB_NAME, null,
DATABASE_VERSION);
}
// Open Database function
public void open() throws SQLException {
// Allow database to be in writable mode
database = dbOpenHelper.getWritableDatabase();
}
// Close Database function
public void close() {
if (database != null)
database.close();
}
// Create Database function
public void InsertNote(String title, String note , String maincat, String subcat) {
ContentValues newCon = new ContentValues();
newCon.put(TITLE, title);
newCon.put(NOTE, note);
newCon.put(MAINCAT, maincat);
newCon.put(SUBCAT, subcat);
open();
database.insert(TABLE_NAME, null, newCon);
close();
}
// Update Database function
public void UpdateNote(long id, String title, String note) {
ContentValues editCon = new ContentValues();
editCon.put(TITLE, title);
editCon.put(NOTE, note);
open();
database.update(TABLE_NAME, editCon, ID + "=" + id, null);
close();
}
// Delete Database function
public void DeleteNote(long id) {
open();
database.delete(TABLE_NAME, ID + "=" + id, null);
close();
}
// List all data function
//String selection = dbOpenHelper.MAINCAT + " = 'quiz'"
// +" AND " + dbOpenHelper.SUBCAT + " = 'test'";
// public Cursor ListAllNotes() {
// return database.query(TABLE_NAME, new String[] { ID, TITLE }, null,
// null, null, null, TITLE);
// }
public Cursor ListAllNotes(String selection) {
return database.query(TABLE_NAME, new String[] { ID, TITLE }, selection,
null, null, null, TITLE);
}
// Capture single data by ID
public Cursor GetOneNote(long id) {
return database.query(TABLE_NAME, null, ID + "=" + id, null, null,
null, null);
}
这里是ListActivity，我想用警报关闭活动
public class dbMainactivty extends ListActivity {
// Declare Variables
public static final String ROW_ID = "row_id";
private static final String TITLE = "title";
private ListView noteListView;
private CursorAdapter noteAdapter;
@SuppressWarnings("deprecation")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Tracker t = ((AnalyticsSampleApp)this.getApplication()).getTracker(TrackerName.APP_TRACKER);
t.setScreenName("dbMainactivty");
t.send(new HitBuilders.AppViewBuilder().build());
// Locate ListView
noteListView = getListView();
// setContentView(R.layout.list_note);
//noteListView = (ListView) findViewById(R.id.listview);
// Prepare ListView Item Click Listener
noteListView.setOnItemClickListener(viewNoteListener);
// Map all the titles into the ViewTitleNotes TextView
String[] from = new String[] { TITLE };
int[] to = new int[] { R.id.ViewTitleNotes };
// Create a SimpleCursorAdapter
noteAdapter = new SimpleCursorAdapter(dbMainactivty.this,
R.layout.list_note, null, from, to);
// Set the Adapter into SimpleCursorAdapter
setListAdapter(noteAdapter);
}
// Capture ListView item click
OnItemClickListener viewNoteListener = new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// Open ViewNote activity
Intent viewnote = new Intent(dbMainactivty.this, ViewNote.class);
// Pass the ROW_ID to ViewNote activity
viewnote.putExtra(ROW_ID, arg3);
startActivity(viewnote);
}
};
@Override
protected void onResume() {
super.onResume();
// Execute GetNotes Asynctask on return to MainActivity
new GetNotes().execute((Object[]) null);
GoogleAnalytics.getInstance(dbMainactivty.this).reportActivityStart(this);
}
@Override
protected void onStop() {
Cursor cursor = noteAdapter.getCursor();
// Deactivates the Cursor
if (cursor != null)
cursor.deactivate();
noteAdapter.changeCursor(null);
super.onStop();
GoogleAnalytics.getInstance(dbMainactivty.this).reportActivityStop(this);
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
Intent i = null;
switch (item.getItemId()) {
case R.id.action_rate:
String webpage = "http://developer.android.com/index.html";
Intent intent2 = new Intent(Intent.ACTION_VIEW, Uri.parse(webpage));
startActivity(intent2);
overridePendingTransition(R.anim.slide_in, R.anim.slide_out);
case R.id.action_share:
i = new Intent();
i.setAction(Intent.ACTION_SEND);
//i.putExtra(Intent.EXTRA_TEXT, feed.getItem(pos).getTitle().toString()+ " to know the answer download http://developer.android.com/index.html");
i.setType("text/plain");
startActivity(i);
return true;
}
return super.onOptionsItemSelected(item);
};
// GetNotes AsyncTask
private class GetNotes extends AsyncTask<Object, Object, Cursor> {
DatabaseConnector dbConnector = new DatabaseConnector(dbMainactivty.this);
@Override
protected Cursor doInBackground(Object... params) {
// Open the database
dbConnector.open();
return dbConnector.ListAllNotes("maincat LIKE 'quiz' AND subcat LIKE 'test'");
}
@Override
protected void onPostExecute(Cursor result) {
noteAdapter.changeCursor(result);
// Close Database
dbConnector.close();
}
}
@Override
protected void onStart() {
super.onStart();
ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
if (conMgr.getActiveNetworkInfo() == null) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage(
"Please check your Internet Connection.")
.setTitle("tilte")
.setCancelable(false)
.setPositiveButton("Exit",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,
int id) {
//loader.cancel(true);
finish();
}
});
AlertDialog alert = builder.create();
alert.show();
} else {
Cursor cursor = noteAdapter.getCursor();
if(cursor != null && cursor.getCount() > 0){
cursor.moveToFirst();
//do your action
//Fetch your data
GoogleAnalytics.getInstance(dbMainactivty.this).reportActivityStart(this);
Toast.makeText(getBaseContext(), "Yipeee!", Toast.LENGTH_SHORT).show();
}
else {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage(
"oops nothing pinned yet! ....")
.setTitle("title")
.setCancelable(false)
.setPositiveButton("Exit",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,
int id) {
//loader.cancel(true);
finish();
}
});
AlertDialog alert = builder.create();
alert.show();
Toast.makeText(getBaseContext(), "No records yet!", Toast.LENGTH_SHORT).show();
}
}
}
}
我正在尝试检查
cursor != null && cursor.getCount()>0如果它变为false，则显示警告
nothing has been pinned yet
但是，即使光标返回数据，也应显示警报仍然显示。
答案 0 :(得分：1)
首先，请查看您的活动的生命周期：http://www.android-app-market.com/wp-content/uploads/2012/03/Android-Activity-Lifecycle.png
正如你所看到的，在onStart（）之后调用onResume（），这意味着检查onStart（）上的光标是行不通的。
其次，您在onResume（）方法上启动AsyncTask（GetNotes），这意味着您此时正在运行并行线程，并且在调用新的GetNotes（）之后无法检查结果.execute（（Object []）null）;
您的问题是您需要在AsyncTask完成之后检查数据加载后光标的空虚（cursor != null && cursor.getCount()>0）。换句话说，在onPostExecute(Cursor result)方法中移动光标上的空白检查。
