我正在尝试使用sqlitedatabase
输入用户的姓名和电话号码,然后将其显示在listview
中。我在数据库中插入细节时没有错误,但当我检查database
是否为空时,即使listview
中显示了元素,它也显示为空。
database
的代码如下:
UserDatabase.java
public class UserDatabase extends SQLiteOpenHelper {
// Table Name
public static final String TABLE_NAME = "UserDataB";
// Table columns
public static final String _ID = "_id";
public static final String NAME = "name";
public static final String NUMBER = "phonenumber";
// Database Information
static final String DB_NAME = "User_Details.DB";
// database version
static final int DB_VERSION = 1;
// Creating table query
private static final String CREATE_TABLE = "create table " + TABLE_NAME + "(" + _ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT, " + NAME + " TEXT NOT NULL, " + NUMBER + " TEXT);";
public UserDatabase(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
DatabaseManager.java
public class DatabaseManager {
private UserDatabase dbHelper;
private Context context;
private SQLiteDatabase database;
public DatabaseManager(Context c) {
context = c;
}
public DatabaseManager open() throws SQLException {
dbHelper = new UserDatabase(context);
database = dbHelper.getWritableDatabase();
return this;
}
public void insert(String name, String number) {
ContentValues contentValue = new ContentValues();
contentValue.put(UserDatabase.NAME, name);
contentValue.put(UserDatabase.NUMBER, number);
database.insert(UserDatabase.TABLE_NAME, null, contentValue);
}
public Cursor fetch() {
String[] columns = new String[] { UserDatabase._ID, UserDatabase.NAME, UserDatabase.NUMBER };
Cursor cursor = database.query(UserDatabase.TABLE_NAME, columns, null, null, null, null, null);
if (cursor != null) {
cursor.moveToFirst();
}
return cursor;
}
public boolean isEmpty(){
SQLiteDatabase db;
db=new UserDatabase(context).getWritableDatabase();
Cursor cursor=db.rawQuery("SELECT * FROM "+UserDatabase.TABLE_NAME,null);
Boolean rowExists;
if (cursor.moveToFirst()){
rowExists=true;
}else {
rowExists=false;
}
return rowExists;
}
}
从listview
填充database
的活动如下:
DetailsActivity.java
public class DetailsActivity extends AppCompatActivity {
private DatabaseManager manager;
private ListView listView;
private SimpleCursorAdapter adapter;
final String[] from=new String[] {UserDatabase.NAME,UserDatabase.NUMBER};
final int[] to=new int[] {R.id.nameDisplay,R.id.phoneDisplay};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_details);
manager = new DatabaseManager(getApplicationContext());
manager.open();
Cursor cursor=manager.fetch();
listView = (ListView) findViewById(R.id.listViewId);
listView.setEmptyView(findViewById(R.id.empty));
adapter = new SimpleCursorAdapter(getApplicationContext(),
R.layout.row_item, cursor, from, to, 0);
adapter.notifyDataSetChanged();
listView.setAdapter(adapter);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(DetailsActivity.this);
LayoutInflater inflater = DetailsActivity.this.getLayoutInflater();
final View dialogView = inflater.inflate(R.layout.custom_dialog, null);
dialogBuilder.setView(dialogView);
final EditText name = (EditText) dialogView.findViewById(R.id.dialogEditNmID);
final EditText phone = (EditText) dialogView.findViewById(R.id.dialogEditPhID);
dialogBuilder.setTitle("Add Details");
dialogBuilder.setPositiveButton("Add", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
if (!TextUtils.isEmpty(name.getText().toString()) &&
!TextUtils.isEmpty(phone.getText().toString())) {
insertData(name.getText().toString(),phone.getText().toString());
Cursor cursor=manager.fetch();
adapter = new SimpleCursorAdapter(getApplicationContext(),
R.layout.row_item, cursor, from, to, 0);
adapter.notifyDataSetChanged();
listView.setAdapter(adapter);
} else {
Toast.makeText(getApplicationContext(),
"Empty field(s)", Toast.LENGTH_SHORT).show();
}
}
});
dialogBuilder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
lertDialog b = dialogBuilder.create();
b.show();
}
});
}
public void insertData(String fname,String phnumber){
manager.insert(fname,phnumber);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();
}
}
即使toast message
中有条目,onClick
test_button
方法中的Empty
始终会显示database
。
有人可以帮忙吗?
答案 0 :(得分:1)
此方法存在逻辑错误
public boolean isEmpty().
如果存在行,为什么返回isEmpty()
为真?:
如果行没有退出,为什么返回false
它为空,现在返回true
。
总之,您返回false
而不是true
和true
而不是false
。
请将您的代码更改为:(阅读评论以获取更多信息!):
public boolean isEmpty(){
SQLiteDatabase db;
db=new UserDatabase(context).getWritableDatabase();
Cursor cursor=db.rawQuery("SELECT * FROM "+UserDatabase.TABLE_NAME,null);
if (cursor.moveToFirst()){
return false; //because its not empty it has something thats why the cursor moved!
}else {
return true; //because it does not have anything and the cursor has nothing so return its really empty!
}
}