我在 Android eclipse 中使用 SQLite，但是它在函数 createEntry 中给了我一个 java.lang.nullpointerexception。我尝试使用 Questoid SQLite 管理器查看数据库文件，它确实显示了创建的表。错误在哪里？
public class Transact {
public static final String KEY_ROWID = "_id";
public static final String KEY_TAG = "saved_tag";
private static final String DATABASE_NAME = "MyDatabaseName";
private static final String DATABASE_TABLE = "tagsTable";
private static final int DATABASE_VERSION = 1;
private DbHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;
private static class DbHelper extends SQLiteOpenHelper{
public DbHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(
"CREATE TABLE " + DATABASE_TABLE + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_TAG + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
public Transact(Context c ){
ourContext = c;
}
public Transact open() throws SQLException{
ourHelper = new DbHelper(ourContext);
ourHelper.getWritableDatabase();
return this;
}
public void close(){
ourHelper.close();
}
public long createEntry(String tagword) {
// TODO Auto-generated method stub
ContentValues cv = new ContentValues();
cv.put(KEY_TAG, tagword);
return ourDatabase.insert(DATABASE_TABLE, "", cv);
}
public String getData() {
// TODO Auto-generated method stub
String[] columns = new String[]{KEY_ROWID, KEY_TAG};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
String result = "";
int iRow = c.getColumnIndex(KEY_ROWID);
int iTag = c.getColumnIndex(KEY_TAG);
for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
result = result + c.getString(iRow) + " " + c.getString(iTag) + "\n";
}
return null;
}
}
Main.java 类中添加按钮的代码：
case R.id.addDB:
boolean doneAdd = true;
try{
String tag = textTag.getText().toString();
Transact entry = new Transact(Main.this);
entry.open();
entry.createEntry(tag);
entry.close();
}catch(Exception e){
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
doneAdd = false;
}finally{
if(doneAdd){
Dialog d = new Dialog(this);
d.setTitle("Addition done");
TextView tv = new TextView(this);
tv.setText("Success");
d.setContentView(tv);
d.show();
}
}
break;