質問とその回答のデータベースを作成する必要があります。sqlitedatabase ブラウザーを使用して作成し、Assets フォルダーに入れました。これは、特定の質問 ID の行を取得するための私のコードです。
いくつかの重要な情報 私のデータベース名は extenalDB です。私のテーブル名は質問です。
coloum を持つ: id,question,ans
ID 201 の質問を検索する必要があります。
question.java show error id undeclared にあるクエリを作成すると。
私はstackoverflowを初めて使用するので、自分のことを明確にすることができなかった場合は質問してください
これは私の DatabaseHelper クラスコードです
public class DatabaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
String DB_PATH =null;
private static String DB_NAME = "extenalDB";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
} // Creates a empty database on the system and rewrites it with your owndatabase.*/
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}}
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public Cursor query(String table,String[] columns, String selection,String[] selectionArgs,String groupBy,String having,String orderBy){
return myDataBase.query("question", null, null, null, null, null, null);
}
}
もう 1 つのクラス question.java では、開始ボタンの質問の回答をクリックすると、その ID がトースト メッセージに表示されます。question.javaのコードは.
public class question extends Activity{
Cursor c=null;
int rid=201;
@Override
public void onCreate(Bundle savedInstanceState) {
Intent mintent = getIntent();
int intValue = mintent.getIntExtra("qtype",0);
super.onCreate(savedInstanceState);
setContentView(R.layout.question);
((Button)findViewById(R.id.button1)).setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
DatabasseHelper myDbHelper = new DatabasseHelper(question.this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
Toast.makeText(question.this, "Success", Toast.LENGTH_SHORT).show();
c=myDbHelper.query("question", null, id + "=" + rid, null, null,null, null);
Toast.makeText(question.this,
"id: " + c.getString(0) + "\n" +
"question: " + c.getString(1) + "\n" +
"ans: " + c.getString(2) + "\n" +
Toast.LENGTH_LONG).show();
}
});
}}