android - 重新启动 Activity 时 SQLite 数据库丢失

Question

我正在创建一个应用程序，用于在数据库中插入数据并从数据库中检索数据。当第一次 Activity 开始时，数据插入数据库并从数据库中检索数据，但是当我重新启动 Activity 并单击按钮从数据库中检索数据时，我的应用程序因错误而关闭。请帮助我??

数据库助手类

public class DataBaseHelper extends SQLiteOpenHelper
{
    public DataBaseHelper(Context context, String name,CursorFactory factory, int version) 
    {
               super(context, name, factory, version);
    }
    // Called when no database exists in disk and the helper class needs
    // to create a new one.
    @Override
    public void onCreate(SQLiteDatabase _db) 
    {
            _db.execSQL(DetailDataBaseAdapter.DATABASE_CREATE);


    }
    // Called when there is a database version mismatch meaning that the version
    // of the database on disk needs to be upgraded to the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) 
    {
            // Log the version upgrade.
            Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");

            // Upgrade the existing database to conform to the new version. Multiple
            // previous versions can be handled by comparing _oldVersion and _newVersion
            // values.
            // The simplest case is to drop the old table and create a new one.
            _db.execSQL("DROP TABLE IF EXISTS " + "TEMPLATE");
            // Create a new one.
            onCreate(_db);
    }

}

数据库适配器类

public class DetailDataBaseAdapter{

    static final String DATABASE_NAME = "phone.db";
    static final int DATABASE_VERSION = 1;
    public static final int NAME_COLUMN = 1;
    // TODO: Create public field for each column in your table.
    // SQL Statement to create a new database.
    static final String DATABASE_CREATE = "create table "+"PHONE"+
                                 "( " +"ID"+" integer primary key autoincrement,"+ "NUMBER  text,SIM text,IMEI text); ";
    // Variable to hold the database instance
    public  SQLiteDatabase db;
    // Context of the application using the database.
    private final Context context;
    // Database open/upgrade helper
    private DataBaseHelper dbHelper;
    public  DetailDataBaseAdapter(Context _context) 
    {
        context = _context;
        dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    public  DetailDataBaseAdapter open() throws SQLException 
    {
        db = dbHelper.getWritableDatabase();
        return this;
    }
    public void close() 
    {
        db.close();
    }
    public  SQLiteDatabase getDatabaseInstance()
    {
        return db;
    }

    public void insertEntry(String number,String sim,String imei)
    {
       ContentValues newValues = new ContentValues();
        // Assign values for each row.
        newValues.put("NUMBER", number);
        newValues.put("SIM",sim);
        newValues.put("IMEI",imei);

        // Insert the row into your table
        db.insert("PHONE", null, newValues);
        ///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
    }

    public String getData(String number)
    {
        Cursor cursor=db.query("PHONE", null, " NUMBER=?", new String[]{number}, null, null, null);
        if(cursor.getCount()<1) // UserName Not Exist
        {
            cursor.close();
            return "NOT EXIST";
        }
        cursor.moveToFirst();
        String sim_id= cursor.getString(cursor.getColumnIndex("NUMBER"));
        cursor.close();
        return sim_id;              
    }

}

主 Activity 类

public class MainActivity extends Activity{
    TextView tv;
    String telNumber,simID,IMEI;
    Button btn,bt;
    TelephonyManager tm;
    DetailDataBaseAdapter detailDataBaseAdapter;
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tm = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        btn = (Button) findViewById(R.id.ok);
        detailDataBaseAdapter=new DetailDataBaseAdapter(this);
        detailDataBaseAdapter=detailDataBaseAdapter.open();
        btn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                 simID = tm.getSimSerialNumber();
                if (simID != null) {
                    tv=(TextView)findViewById(R.id.tv_sim_no);
                    tv.setText(simID);
                }
                // ---get the phone number---
             telNumber = tm.getLine1Number();
                if (telNumber != null) {
                    tv=(TextView)findViewById(R.id.tv_phone_no);
                    tv.setText(telNumber);
                }
                // ---get the IMEI number---
                 IMEI = tm.getDeviceId();
                if (IMEI != null) {
                    tv=(TextView)findViewById(R.id.tv_imei_no);
                    tv.setText(IMEI);
                }

                detailDataBaseAdapter.insertEntry(telNumber,simID,IMEI);
            }
        });
    bt=(Button)findViewById(R.id.getDetail);
        bt.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                String storedPassword=detailDataBaseAdapter.getData(telNumber);


                Toast.makeText(MainActivity.this, storedPassword, Toast.LENGTH_LONG).show();

            }
        });

    }
}

日志

FATAL EXCEPTION: main
 Process: com.example.phone_detail, PID: 10548
 E/AndroidRuntime(10548): java.lang.IllegalArgumentException: the bind value at index 1 is null
    at android.database.sqlite.SQLiteProgram.bindString(SQLiteProgram.java:164)
    at android.database.sqlite.SQLiteProgram.bindAllArgsAsStrings(SQLiteProgram.java:200)
    at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:47)
    at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1316)
    at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1163)
    at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1034)
    at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1202)
    at com.example.phone_detail.DetailDataBaseAdapter.getData(DetailDataBaseAdapter.java:59)
    at com.example.phone_detail.MainActivity$2.onClick(MainActivity.java:59)

Answer 1

logCat 表示您正在绑定(bind) null 以在您的 getData 方法中进行查询 - 因此您可能正在使用 null 参数调用此方法。在调用 db.query

之前尝试检查参数是否为 null