我在Android Studio中获得了这个DataBaseOpenHelper类：
public class DatabaseOpenHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "cf_db.db";
public static final String TABLE_NAME = "cf_table";
public static final String CF = "CF";
public static final String COL1 = "Name";
public static final String COL2 = "Surname";
public static final String COL3 = "Sex";
public static final String COL4 = "Birthday";
public static final String COL5 = "PlaceOfBirth";
public DatabaseOpenHelper(Context context) {
super(context, DATABASE_NAME, null, 2);
SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL("CREATE TABLE " + TABLE_NAME +
"(" + CF + " TEXT PRIMARY KEY, " + COL1 + " TEXT NOT NULL, " +
COL2 + " TEXT NOT NULL," + COL3 + " TEXT NOT NULL," + COL4 +
" TEXT NOT NULL," + COL5 + " TEXT NOT NULL);");
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(sqLiteDatabase);
}
public boolean insertData(String cf, String name, String surname, String sex, String year,
String month, String day, String place) {
String date = day + "/" + month + "/" + year;
SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(CF, cf);
contentValues.put(COL1, name);
contentValues.put(COL2, surname);
contentValues.put(COL3, sex);
contentValues.put(COL4, date);
contentValues.put(COL5, place);
long id = sqLiteDatabase.insert(TABLE_NAME, null, contentValues);
sqLiteDatabase.close();
return (id != -1);
}
public String getTableAsString(SQLiteDatabase db, String tableName) {
Log.d("ciao", "getTableAsString called");
String tableString = String.format("Table %s:\n", tableName);
Cursor allRows = db.rawQuery("SELECT * FROM " + tableName, null);
if (allRows.moveToFirst()) {
String[] columnNames = allRows.getColumnNames();
do {
for (String name : columnNames) {
tableString += String.format("%s: %s\n", name,
allRows.getString(allRows.getColumnIndex(name)));
}
tableString += "\n";
} while (allRows.moveToNext());
}
return tableString;
}
一切似乎都可以进行到这里，我可以使用getTableAsString方法打印整个表而没有问题。
现在，我需要另一个活动中的新方法来搜索此cf_table，并将COL2（姓氏）作为输入。
公共类ThirdActivity扩展了AppCompatActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_third);
EditText editText_search;
Button button_ok;
editText_search = findViewById(R.id.editText4);
String searchtext = editText_search.getText().toString();
button_ok = findViewById(R.id.button_ok);
button_ok.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.d("ciao", searchtext); //doesn't print this
CFsearch(searchtext);
}
}
);
}
public String CFsearch(String search) {
DatabaseOpenHelper db = new DatabaseOpenHelper(getApplicationContext());
String tag = "print";
SQLiteDatabase sqldb = db.getDB(db);
String result = String.format("Table %s:\n", "cf_table");
Cursor cursor = sqldb.rawQuery("SELECT CF FROM cf_table " +
"WHERE Surname = ?", new String[] {search});
if (cursor.moveToFirst()) {
String[] columnNames = cursor.getColumnNames();
do {
for (String name : columnNames) {
result += String.format("%s: %s\n", name,
cursor.getString(cursor.getColumnIndex(name)));
}
result += "\n";
} while (cursor.moveToNext());
}
Log.d("debug", result);
return result;
}
}
我使用了getTableAsString方法的相同实现。 我收到错误“没有这样的列：COL2”。我不明白为什么有该表，并且可以按我所说的打印它，但是我无法在本活动中完成我需要的特定任务（在查询中说明：为该表提取CF（主键））具有COL2 =输入的行）。该错误显然在rawQuery的行中。
我已经清理并重建了项目，已经关闭了Android Studio并重新启动了模拟器。我在Mac上，几个月前我遇到了相同的错误，该错误是通过“重建并重新启动”过程解决的。