嗨，堆栈溢出成员 我创建了一个应用程序，用户可以在其中将收藏夹项目添加到收藏夹列表中。 但是我面临的问题是，当我单击"添加到收藏夹"按钮时，该项目会添加到列表底部而不是顶部。
其次，当我多次单击同一项目添加到收藏夹项目时，这会多次添加该项目，而不仅仅是一次。 我怎样才能只将其添加到列表中一次而不是多次。这是我的活动和数据库代码。
我的数据库管理员.class
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
// TO USE:
// Change the package (at top) to match your project.
// Search for "TODO", and make the appropriate changes.
public class DBAdapter {
/////////////////////////////////////////////////////////////////////
// Constants & Data
/////////////////////////////////////////////////////////////////////
// For logging:
private static final String TAG = "DBAdapter";
// DB Fields
public static final String KEY_ROWID = "_id";
public static final int COL_ROWID = 0;
/*
* CHANGE 1:
*/
// TODO: Setup your fields here:
public static final String KEY_NAME = "name";
public static final String KEY_STUDENTNUM = "studentnum";
public static final String KEY_FAVCOLOUR = "favcolour";
// TODO: Setup your field numbers here (0 = KEY_ROWID, 1=...)
public static final int COL_NAME = 1;
public static final int COL_STUDENTNUM = 2;
public static final int COL_FAVCOLOUR = 3;
public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_NAME, KEY_STUDENTNUM, KEY_FAVCOLOUR};
// DB info: it's name, and the table we are using (just one).
public static final String DATABASE_NAME = "MyDb";
public static final String DATABASE_TABLE = "mainTable";
// Track DB version if a new version of your app changes the format.
public static final int DATABASE_VERSION = 2;
private static final String DATABASE_CREATE_SQL =
"create table " + DATABASE_TABLE
+ " (" + KEY_ROWID + " integer primary key autoincrement, "
/*
* CHANGE 2:
*/
// TODO: Place your fields here!
// + KEY_{...} + " {type} not null"
// - Key is the column name you created above.
// - {type} is one of: text, integer, real, blob
// (http://www.sqlite.org/datatype3.html)
// - "not null" means it is a required field (must be given a value).
// NOTE: All must be comma separated (end of line!) Last one must have NO comma!!
+ KEY_NAME + " text not null, "
+ KEY_STUDENTNUM + " integer not null, "
+ KEY_FAVCOLOUR + " string not null"
// Rest of creation:
+ ");";
// Context of application who uses us.
private final Context context;
private DatabaseHelper myDBHelper;
private SQLiteDatabase db;
/////////////////////////////////////////////////////////////////////
// Public methods:
/////////////////////////////////////////////////////////////////////
public DBAdapter(Context ctx) {
this.context = ctx;
myDBHelper = new DatabaseHelper(context);
}
// Open the database connection.
public DBAdapter open() {
db = myDBHelper.getWritableDatabase();
return this;
}
// Close the database connection.
public void close() {
myDBHelper.close();
}
// Add a new set of values to the database.
public long insertRow(String name, int studentNum, String favColour) {
/*
* CHANGE 3:
*/
// TODO: Update data in the row with new fields.
// TODO: Also change the function's arguments to be what you need!
// Create row's data:
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_STUDENTNUM, studentNum);
initialValues.put(KEY_FAVCOLOUR, favColour);
// Insert it into the database.
return db.insert(DATABASE_TABLE, null, initialValues);
}
// Delete a row from the database, by rowId (primary key)
public boolean deleteRow(long rowId) {
String where = KEY_ROWID + "=" + rowId;
return db.delete(DATABASE_TABLE, where, null) != 0;
}
public void deleteAll() {
Cursor c = getAllRows();
long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
if (c.moveToFirst()) {
do {
deleteRow(c.getLong((int) rowId));
} while (c.moveToNext());
}
c.close();
}
// Return all data in the database.
public Cursor getAllRows() {
String where = null;
Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
where, null, null, null, null, null);
if (c != null) {
c.moveToFirst();
}
return c;
}
// Get a specific row (by rowId)
public Cursor getRow(long rowId) {
String where = KEY_ROWID + "=" + rowId;
Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
where, null, null, null, null, null);
if (c != null) {
c.moveToFirst();
}
return c;
}
// Change an existing row to be equal to new data.
public boolean updateRow(long rowId, String name, int studentNum, String favColour) {
String where = KEY_ROWID + "=" + rowId;
/*
* CHANGE 4:
*/
// TODO: Update data in the row with new fields.
// TODO: Also change the function's arguments to be what you need!
// Create row's data:
ContentValues newValues = new ContentValues();
newValues.put(KEY_NAME, name);
newValues.put(KEY_STUDENTNUM, studentNum);
newValues.put(KEY_FAVCOLOUR, favColour);
// Insert it into the database.
return db.update(DATABASE_TABLE, newValues, where, null) != 0;
}
/////////////////////////////////////////////////////////////////////
// Private Helper Classes:
/////////////////////////////////////////////////////////////////////
/**
* Private class which handles database creation and upgrading.
* Used to handle low-level database access.
*/
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase _db) {
_db.execSQL(DATABASE_CREATE_SQL);
}
@Override
public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading application's database from version " + oldVersion
+ " to " + newVersion + ", which will destroy all old data!");
// Destroy old database:
_db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
// Recreate new database:
onCreate(_db);
}
}
}
我最喜欢的列表活动..
DBAdapter myDb;
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.favoritediseases);
openDB();
populateListViewFromDB();
registerListClickCallback();
// this code is used for the action bar color change//
ActionBar bar = getActionBar();
bar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#6B8E23")));
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
}
@Override
protected void onDestroy() {
super.onDestroy();
closeDB();
}
private void openDB() {
myDb = new DBAdapter(this);
myDb.open();
}
private void closeDB() {
myDb.close();
}
/*
* UI Button Callbacks
*/
private void populateListViewFromDB() {
Cursor cursor = myDb.getAllRows();
// Allow activity to manage lifetime of the cursor.
// DEPRECATED! Runs on the UI thread, OK for small/short queries.
startManagingCursor(cursor);
// Setup mapping from cursor to view fields:
String[] fromFieldNames = new String[]
{DBAdapter.KEY_NAME, DBAdapter.KEY_STUDENTNUM};
int[] toViewIDs = new int[]
{R.id.item_name};
// Create adapter to may columns of the DB onto elemesnt in the UI.
SimpleCursorAdapter myCursorAdapter =
new SimpleCursorAdapter(
this, // Context
R.layout.item_layout, // Row layout template
cursor, // cursor (set of DB records to map)
fromFieldNames, // DB Column names
toViewIDs // View IDs to put information in
);
// Set the adapter for the list view
ListView myList = (ListView) findViewById(R.id.favlistView1);
myList.setAdapter(myCursorAdapter);
}
private void registerListClickCallback() {
ListView myList = (ListView) findViewById(R.id.favlistView1);
//This code is for to delete the single item from the listview of favorite list
myList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
int arg2, final long arg3) {
Cursor cursor = myDb.getRow(arg3);
if (cursor.moveToFirst()) {
new AlertDialog.Builder(FavoriteDiseases.this)
.setTitle("Delete Item")
.setMessage("Do you want to delete this disease?")
.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// continue with delete
myDb.deleteRow(arg3);
populateListViewFromDB();
}
})
.setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// do nothing
}
})
.show();
}
return true;
}
});
//this is the code used from starting activity from the favorite list database.
myList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View viewClicked,
int position, long idInDB) {
Cursor cursor = myDb.getRow(idInDB);
if (cursor.moveToFirst()) {
String name = cursor.getString(DBAdapter.COL_NAME);
if (name.equals("Atherosclerosis")){
startActivity(new Intent(FavoriteDiseases.this,Atherosclerosis.class));
}else if
(name.equals("Coronary Heart Disease")){
startActivity(new Intent(FavoriteDiseases.this,CoronaryHeartDisease.class));
}else if (name.equals("Stable Angina")){
startActivity(new Intent(FavoriteDiseases.this,StableAngina.class));
}else if (name.equals("Acute Coronary Syndrome")){
startActivity(new Intent(FavoriteDiseases.this,AcuteCoronarySyndrome.class));
}else if (name.equals("Myocardial Infarction")){
startActivity(new Intent(FavoriteDiseases.this,MyocardialInfarction.class));
}else if (name.equals("Unstable Angina")){
startActivity(new Intent(FavoriteDiseases.this,UnstableAngina.class));
}else if (name.equals("Acute Heart Failure")){
startActivity(new Intent(FavoriteDiseases.this,AcuteHeartFailure.class));
}
}
cursor.close();
updateItemForId(idInDB);
}
});}
private void updateItemForId(long idInDB) {
Cursor cursor = myDb.getRow(idInDB);
if (cursor.moveToFirst()) {
cursor.getLong(DBAdapter.COL_ROWID);
String name = cursor.getString(DBAdapter.COL_NAME);
int studentNum = cursor.getInt(DBAdapter.COL_STUDENTNUM);
String favColour = cursor.getString(DBAdapter.COL_FAVCOLOUR);
favColour += "!";
myDb.updateRow(idInDB, name, studentNum, favColour);
}
cursor.close();
populateListViewFromDB();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.favorite_diseases, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Take appropriate action for each action item click
switch (item.getItemId()) {
case R.id.action_clear:
new AlertDialog.Builder(this)
.setTitle("Delete List")
.setMessage("Do you want to clear all?")
.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// continue with delete
myDb.deleteAll();
populateListViewFromDB();
}
})
.setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// do nothing
}
})
.show();
return true;
}
return true;
}}
我添加到列表中的最终代码
case R.id.id_favorit:
// Add it to the DB and re-draw the ListView
myDb.insertRow("Atherosclerosis", 0, "");
Toast.makeText(getApplicationContext(), "Item Added to Favorite List!", Toast.LENGTH_SHORT).show();
favClicked=true;
invalidateOptionsMenu();
return true;
似乎您只想以相反的顺序从数据库中获取结果。将检索它们的函数更改为按降序排列的 ORDER BY 您的 rowid 将完成以下伎俩：
// Return all data in the database.
public Cursor getAllRows() {
String where = null;
Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
where, null, null, null, KEY_ROWID + " DESC", null);
if (c != null) {
c.moveToFirst();
}
return c;
}
关于您的第二个问题，您应该在插入之前检查收藏夹是否存在。问题是你如何定义你的独特性。例如，如果您不想要两个同名的"收藏夹"，则需要在插入函数中添加一个复选标记：
// Add a new set of values to the database, unless the name already exists.
public long insertRow(String name, int studentNum, String favColour) {
Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS,
KEY_NAME + "='" + name + "'", null, null, null, null, null);
if (c.getCount() > 0) {
return -1;
}
c.close();
/*
* CHANGE 3:
*/
// TODO: Update data in the row with new fields.
// TODO: Also change the function's arguments to be what you need!
// Create row's data:
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_STUDENTNUM, studentNum);
initialValues.put(KEY_FAVCOLOUR, favColour);
// Insert it into the database.
return db.insert(DATABASE_TABLE, null, initialValues);
}