在Android应用中实现SQLite数据库

Question

我的应用程序允许用户创建文本消息并指定他们希望发送的时间和日期。不过我遇到了一些问题。由于Pending intent的性质，我无法为每条消息创建一个新的intent。因此，如果用户在执行挂起的意图之前提交要发送的新文本，它将覆盖之前的消息。因此，就目前而言，我不能有多个消息排队等待发送。

我的解决方案是维护一个包含各种消息细节的SQLite数据库，并简单地使用数据库中接下来出现的消息更新挂起的意图。这还有一个额外的好处，即使显示要发送的当前消息列表和编辑要发送的消息的实现简单得多。

问题是我认为我没有正确设置数据库。当我在调试模式下运行时，它似乎没有进入我的数据库助手类(MessagesHelper)并实例化数据库变量。我不确定我做错了什么，一直遵循android SQLite开发指南。如果你能给我任何帮助/提示，我将不胜感激。

表契约类

public class Messages {
    private Messages(){}
    public static abstract class Texts implements BaseColumns {
        public static final String TABLE_NAME = "texts";
        public static final String DEFAULT_SORT_ORDER = "stime DESC";
        public static final String COLUMN_NAME_RECIPIENT = "recipient";
        public static final String COLUMN_NAME_MESSAGE = "message";
        public static final String COLUMN_NAME_SEND_TIME = "stime";
        public static final String AUTHORITY = "com.rastelliJ.deferredSMS";
    }
}

数据库辅助类

public class MessagesHelper extends SQLiteOpenHelper{
    private static final String TAG = "MessagesHelper";
    private static final String TEXT_TYPE = " TEXT";
    private static final String COMMA_SEP = ",";
    private static final String SQL_CREATE_ENTRIES =
                                    "CREATE TABLE " + Messages.Texts.TABLE_NAME + " (" +
                                    Messages.Texts._ID + " INTEGER PRIMARY KEY," +
                                    Messages.Texts.COLUMN_NAME_MESSAGE + TEXT_TYPE + COMMA_SEP +
                                    Messages.Texts.COLUMN_NAME_RECIPIENT + TEXT_TYPE + COMMA_SEP +
                                    Messages.Texts.COLUMN_NAME_SEND_TIME + TEXT_TYPE + " )";
    private static final String SQL_DELETE_ENTRIES = "DROP TABLE IF EXISTS " + Messages.Texts.TABLE_NAME;
    // If you change the database schema, you must increment the database version.
    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "Messages.db";
    MessagesHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_ENTRIES);
    }
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // This database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL(SQL_DELETE_ENTRIES);
        onCreate(db);
    }
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        onUpgrade(db, oldVersion, newVersion);
    }
    }

主要活动

public class MainActivity extends FragmentActivity {
private CustomDateTimePicker customDT;
private MessagesHelper mDbHelper;
private EditText phoneName, messageText;
private String phoneNum, alarmtime;
private TextView alarmText;
private Button sendButt;
private int pickerHour = 0, 
            pickerMin = 0, 
            pickerYear = 0, 
            pickerMonth = 0, 
            pickerDay = 0;
private static final int CONTACT_PICKER_RESULT = 1;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //Set up the custom Date Time Picker
    customDT = new CustomDateTimePicker(this, new  CustomDateTimePicker.ICustomDateTimeListener() {
            public void onSet(Dialog dialog, Calendar calendarSelected,
                Date dateSelected, int year, String monthFullName,
                String monthShortName, int monthNumber, int date,
                String weekDayFullName, String weekDayShortName,
                int hour24, int hour12, int min, int sec,
                String AM_PM) { 
                    // Do something with the time chosen by the user
                    pickerYear = year;
                    pickerMonth = monthNumber;
                    pickerDay = date;
                    pickerHour = hour24;
                    pickerMin = min;
                    alarmtime = weekDayFullName + ", " + monthFullName + " " + date + ", " + year + " " + hour12 + ":" + pickerMin + " " + AM_PM;
                    alarmText.setText("Send Date: " + alarmtime);
                }
            public void onCancel() {}
        });
    customDT.set24HourFormat(false);
    customDT.setDate(Calendar.getInstance());
    findViewById(R.id.startTimeSetDialog).setOnClickListener(new OnClickListener() 
    {
            public void onClick(View v) {
                customDT.showDialog();
            }
        });
    // Setup global variables
    phoneName = (EditText)findViewById(R.id.phoneNo);
    messageText = (EditText)findViewById(R.id.txtMessage);
    sendButt = (Button)findViewById(R.id.btnSendSMS);
    alarmText = (TextView)findViewById(R.id.alarmPrompt);
    //Create/Find DB
    mDbHelper = new MessagesHelper(this);
    // Start Contact finder
    phoneName.setOnClickListener(new View.OnClickListener() 
    {
        public void onClick(View v) 
        {
            Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI);
            startActivityForResult(intent, CONTACT_PICKER_RESULT);
        }
    });
    // "Send" the message
    sendButt.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v) {
            //Make sure the fields are filled
            if (phoneName.getText().toString().trim().length() == 0)
            {
                Toast.makeText(getApplicationContext(), "Please enter a phone number", Toast.LENGTH_LONG).show();
                return;
            }
            if (messageText.getText().toString().trim().length() == 0)
            {
                Toast.makeText(getApplicationContext(), "Please enter your message", Toast.LENGTH_LONG).show();
                return;
            }
            //Create a calendar variable that equates to the desired time to be sent
            Calendar cal = Calendar.getInstance();
            cal.set(Calendar.YEAR, pickerYear);
            cal.set(Calendar.MONTH, pickerMonth);
            cal.set(Calendar.DATE, pickerDay);
            cal.set(Calendar.HOUR_OF_DAY, pickerHour);
            cal.set(Calendar.MINUTE, pickerMin);
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
            //Set up the pending intent and assign put it in the alarm manger
            //will change this process once db is set up proper
            Intent sIntent = new Intent(MainActivity.this, SendTService.class);
            sIntent.putExtra("phoneNo", phoneNum.toString());
            sIntent.putExtra("msgTxt", messageText.getText().toString());
            PendingIntent psIntent = PendingIntent.getService(MainActivity.this,0, sIntent, PendingIntent.FLAG_CANCEL_CURRENT);
            AlarmManager alarm = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
            alarm.set(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), psIntent);
            //Add the latest message to the db
            SQLiteDatabase db = mDbHelper.getWritableDatabase();
            ContentValues values = new ContentValues();
            values.put(Messages.Texts.COLUMN_NAME_MESSAGE, messageText.getText().toString());
            values.put(Messages.Texts.COLUMN_NAME_RECIPIENT, phoneNum.toString());
            values.put(Messages.Texts.COLUMN_NAME_SEND_TIME, cal.toString());
            db.insert(Messages.Texts.TABLE_NAME, null, values);
            //Clear all the fields and let the user know what's going on
            phoneName.setText("");
            messageText.setText("");
            alarmText.setText("");
            Toast.makeText(getApplicationContext(), "Your Message will be sent on " + alarmtime, Toast.LENGTH_LONG).show();
        }
    });
}
//Associated with the Contact picker getting it's results
@Override  
protected void onActivityResult(int requestCode, int resultCode, Intent data) {  
    if (resultCode == RESULT_OK) {  
        switch (requestCode) {  
            case CONTACT_PICKER_RESULT:
                Cursor cursor = null;  
                String phoneNumber = "";
                List<String> allNumbers = new ArrayList<String>();
                int phoneIdx = 0;
                try {  
                    Uri result = data.getData();  
                    String id = result.getLastPathSegment();  
                    cursor = getContentResolver().query(Phone.CONTENT_URI, null, Phone.CONTACT_ID + "=?", new String[] { id }, null);  
                    phoneIdx = cursor.getColumnIndex(Phone.DATA);
                    if (cursor.moveToFirst())
                    {
                        while (cursor.isAfterLast() == false)
                        {
                            phoneNumber = cursor.getString(phoneIdx);
                            allNumbers.add(phoneNumber);
                            cursor.moveToNext();
                        }
                    } 
                    else 
                    {
                        //no results actions
                    }  
                } 
                catch (Exception e) 
                {  
                   //error actions
                } 
                finally 
                {  
                    if (cursor != null) cursor.close();
                    final CharSequence[] items = allNumbers.toArray(new String[allNumbers.size()]);
                    AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext());
                    builder.setTitle("Choose a number");
                    builder.setItems(items, new DialogInterface.OnClickListener() 
                    {
                        public void onClick(DialogInterface dialog, int item) 
                        {
                            phoneNum = items[item].toString();
                            phoneNum = phoneNum.replace("-", "");
                            phoneName.setText(phoneNum);
                        }
                    });
                    AlertDialog alert = builder.create();
                    if(allNumbers.size() > 1)
                    {
                        alert.show();
                    } 
                    else 
                    {
                        phoneNum = phoneNumber.toString();
                        phoneNum = phoneNum.replace("-", "");
                        phoneName.setText(phoneNum);
                    }
                    if (phoneNumber.length() == 0) 
                    {  
                        //no numbers found actions  
                    }  
                }  
                break;  
            }  
        } 
    else 
    {
       //activity result error actions
    }  
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}
}

Answer 1

我最初的猜测:您的SQL_CREATE_ENTRIES语句缺少CREATE TABLE语句末尾的分号。在谷歌记事本的例子和我所有的数据库中，我总是包括分号，从来没有出现过问题。