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@H_502_8@所需的许可：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>@H_502_8@
我添加了一个，ListView@H_502_8@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);
/* Yes, it saved to our database. But there is no reason for us to read from
* it too when we have the prime object right here. So just add it to the
* adapter and be done */
//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;
}
/**
* If this is too confusing you can ignore it for Now.
* However, I recommend understanding the android UIs before diving in to database storage.
* Take a look at this link:
* http://www.vogella.com/tutorials/AndroidListView/article.html
*/
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) {
/* This method will automagically get called for every item in the list.
* This is an ARRAY adapter. So it has a list of the data we passed in on
* the constructor. So by calling "this" we are accessing it like it were a list
* which it really is. */
final Prime prime = this.getItem(position);
if (view == null) {
view = LayoutInflater.from(MainActivity.this)
.inflate(android.R.layout.simple_list_item_2, null);
}
/* if you look at simple_list_item_2, you will see two textViews. text1 and text2.
* Normally you would create this view yourself, but like i said, that is not the
* reason I am here */
// 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;
}
}
@H_502_8@更改了查询并添加了两种方法，它们将分别转换Prime@H_502_8@为ContentValues@H_502_8@对象和Cursor@H_502_8@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 + "(" +
/* This must be in same order everywhere! */
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);
/* Something else to note: I changed the column types. You had text for these,
* which is fine. But the object that you are storing in each of these is not
* a string. So for consistency store the object as its original class type:
* PrimeNo == integer
* Datetime == long (milliseconds)
* This also makes it so sorting is much easier */
}
@Override
public void onUpgrade(sqliteDatabase db, int oldVersion, int newVersion) {
db.execsql("DROP TABLE IF EXISTS " + TABLE_PRIME);
onCreate(db);
}
/**
* You want to save the entire Prime object at once. Not bits and pieces.
*
* @param prime
*/
public void addPrime(Prime prime) {
ContentValues values = writePrime(prime);
sqliteDatabase db = getWritableDatabase();
db.insert(TABLE_PRIME, null, values);
/* DON'T FORGET TO CLOSE YOUR DATABASE! */
db.close();
}
/**
* Again, you want to receive the entire prime object at once. Not bits.
*
* @return List of prevIoUs prime objects
*/
public List<Prime> getPrimeObjects() {
final List<Prime> primes = new ArrayList<Prime>();
final sqliteDatabase db = getWritableDatabase();
/* Normally i would use this line of code:
final Cursor c = db.rawQuery("SELECT * FROM " + TABLE_PRIME, null);
but, you want to be sure you will get them order by DATE so you kNow
the first prime in the list is the last added. so I switched the query to this:
*/
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.
/* After queried the first item will be our starting point */
c.moveToFirst();
while (c.moveToNext()) {
Prime p = buildPrime(c);
//check not null
if (p != null)
primes.add(p); //add to list
}
/* DON'T FORGET TO CLOSE YOUR DATABASE AND CURSOR! */
c.close();
db.close();
return primes;
}
/**
* Convert the Cursor object back in to a prime number
*
* @param cursor Cursor
* @return Prime
*/
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;
}
/**
* Convert the prime object in to ContentValues to write to DB
*
* @param prime prime
* @return ContentValues
*/
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;
}
}
@H_502_8@我只是更改了值类型。Prime@H_502_8@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;
}
}
@H_502_8@
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