好的，既然您上传了项目，我 想 我已经按照您想要的方式进行了工作。尽管如此，它仍在工作。
有几个错误-主要是逻辑错误。我尽我所能地发表评论，以便您了解我为什么/什么都做。
我没有评论的一件事是
AndroidManifest所需的许可：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
您可以在此处下载该项目，也可以只看一下代码片段：
主要活动
我添加了一个，
ListView以便您可以看到所有素数。还更改了我们从数据库获取数据的方式/位置以及保存到数据库的方式。
public class MainActivity extends ActionBarActivity { private static final String TAG = MainActivity.class.getSimpleName(); private int max = 500; private TextView primeText; private int previousPrimeNumber; private List<Prime> primes; private PrimeAdapter adapter; private MyDBHandler dbManager; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); primeText = (TextView) findViewById(R.id.primeText); //get the object from previous session. Remember these are sorted by date dbManager = new MyDBHandler(this); primes = dbManager.getPrimeObjects(); //get the first prime. (AKA the last one added) if (primes.size() != 0) { previousPrimeNumber = primes.get(0).get_primeno(); //get the first item primeText.setText(String.valueOf(previousPrimeNumber)); } else { previousPrimeNumber = 2; } //create list view and adapter to display the data ListView listView = (ListView) findViewById(R.id.listView); adapter = new PrimeAdapter(this, primes); listView.setAdapter(adapter); findViewById(R.id.primeButton).setonClickListener(new View.onClickListener() { @Override public void onClick(View v) { int primeNumber = -1; //increment previousPrimeNumber by one so we wont keep using previousPrimeNumber for (int i = previousPrimeNumber + 1; i <= max; i++) { if (isPrimeNumber(i)) { primeNumber = i; primeText.setText(String.valueOf(i)); previousPrimeNumber = i + 1; break; } } if (primeNumber != -1) { Prime prime = new Prime(primeNumber); dbManager.addPrime(prime); //The adapter is looking at the list primes. So add it to the top and notify primes.add(0, prime); adapter.notifyDataSetChanged(); } else { Log.e(TAG, "Oops, there was an error. Invalid prime number"); } } }); } public boolean isPrimeNumber(int number) { for (int i = 2; i <= number / 2; i++) { if (number % i == 0) { return false; } } return true; } private class PrimeAdapter extends ArrayAdapter<Prime> { public PrimeAdapter(Context context, List<Prime> primes) { // I am just using androids views. (android.R.id...) super(context, android.R.layout.simple_list_item_2, primes); } @Override public View getView(int position, View view, ViewGroup parent) { final Prime prime = this.getItem(position); if (view == null) { view = LayoutInflater.from(MainActivity.this) .inflate(android.R.layout.simple_list_item_2, null); } // Notice I am referencing android.R.id. and not R.id. That is cause I am lazy and // didn't create my own views. TextView tv1 = (TextView) view.findViewById(android.R.id.text1); TextView tv2 = (TextView) view.findViewById(android.R.id.text2); tv1.setText(String.valueOf(prime.get_primeno())); tv2.setText(prime.getDateTimeFormatted()); //now return the view so the listView knows to show it return view; } }MyDBHandler：
更改了查询并添加了两种方法，它们将分别转换
Prime为
ContentValues对象和
Cursor质数。
public class MyDBHandler extends SQLiteOpenHelper { private static final int DATAbase_VERSION = 1; private static final String DATAbase_NAME = "prime.db"; public static final String TABLE_PRIME = "prime"; public static final String COLUMN_ID = "_id"; public static final String COLUMN_PRIMENO = "primeno"; public static final String COLUMN_DATETIME = "datetime"; public MyDBHandler(Context context) { super(context, DATAbase_NAME, null, DATAbase_VERSION); } @Override public void onCreate(SQLiteDatabase db) { String query = "CREATE TABLE " + TABLE_PRIME + "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + // ID will be index 0 COLUMN_PRIMENO + " INTEGER, " + // Prime will be index 1 COLUMN_DATETIME + " LONG);"; // Date will be index 2 db.execSQL(query); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS " + TABLE_PRIME); onCreate(db); } public void addPrime(Prime prime) { ContentValues values = writePrime(prime); SQLiteDatabase db = getWritableDatabase(); db.insert(TABLE_PRIME, null, values); db.close(); } public List<Prime> getPrimeObjects() { final List<Prime> primes = new ArrayList<Prime>(); final SQLiteDatabase db = getWritableDatabase(); final Cursor c = db.query(TABLE_PRIME, new String[]{COLUMN_ID, COLUMN_PRIMENO, COLUMN_DATETIME}, null, null, null, null, //much null. So wow. COLUMN_DATETIME + " DESC"); //order in descending. c.moveToFirst(); while (c.moveTonext()) { Prime p = buildPrime(c); //check not null if (p != null) primes.add(p); //add to list } c.close(); db.close(); return primes; } private Prime buildPrime(Cursor cursor) { final Prime prime = new Prime(); prime.set_id(cursor.getInt(0)); // id index as stated above prime.set_primeno(cursor.getInt(1)); // prime index as stated above prime.setDateTime(cursor.getLong(2)); // date index as stated above return prime; } private ContentValues writePrime(Prime prime) { ContentValues values = new ContentValues(); values.put(COLUMN_PRIMENO, prime.get_primeno()); //must insert first values.put(COLUMN_DATETIME, prime.getDateTime()); //must insert second return values; }}主要：
我只是更改了值类型。
Prime的目的是存储一个素数整数。那么，为什么不将该字段设为整数呢？
public class Prime { private static final String format = "yyyy-MM-dd HH:mm:ss"; private static final SimpleDateFormat formatter = new SimpleDateFormat(format, Locale.ENGLISH); private int _id; private int _primeno; private long dateTime = 0; //this is in milliseconds. Makes it easier to manage public Prime() { } public Prime(int primeNumber) { //create a new prime object with a prime already known. set the date while we are at it this._primeno = primeNumber; this.dateTime = System.currentTimeMillis(); } public void set_id(int _id) { this._id = _id; } public void set_primeno(int _primeno) { this._primeno = _primeno; } public int get_id() { return _id; } public int get_primeno() { return _primeno; } public long getDateTime() { return dateTime; } public String getDateTimeFormatted() { if (dateTime == 0) { dateTime = System.currentTimeMillis(); } Date date = new Date(dateTime); return formatter.format(date); } public void setDateTime(long dateTime) { this.dateTime = dateTime; }}
