java - sqlite 数据库返回空对象引用

Question

我是安卓新手。我有一个应用程序，当我单击发送按钮时，我在应用程序中收到错误:

SQLiteDatabase.execSQL(java.lang.String,java.lang.object)on a null object reference.

这是我的数据库代码:

public class MyDatabase extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "contact_db" ;
    public static final String TABLE_NAME = "contact_msg" ;
    public static final String COL_1 = "id" ;
    public static final String COL_2 = "phoneNumber" ;
    public static final String COL_3 = "text" ;

    static SQLiteDatabase mDatabase;


    public MyDatabase(@Nullable Context context) {
        super(context, DATABASE_NAME, null,1);

    }

    @Override
    public void onCreate(SQLiteDatabase mDatabase) {
        mDatabase.execSQL("CREATE TABLE " + TABLE_NAME + " ( " +COL_1+ " INTEGEER PRIMARY KEY AUTOINCREMENT ," + COL_2 + "VARCHAR, "
                +COL_3+ "VARCHAR )");

//        mDatabase = openOrCreateDatabase(DATABASE_NAME, MODE_PRIVATE, null);
    }

    @Override
    public void onUpgrade(SQLiteDatabase mDatabase, int i, int i1) {
        mDatabase.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
        onCreate(mDatabase);
    }

    public static void addContacts(String phoneNumber, String text, Context context){


        if (phoneNumber.isEmpty()){
            //    phoneEditText.setError("phoneNumber can not be empty...");
            //    phoneEditText.requestFocus();
            return;
        }

        String sql = " INSERT INTO contact_msg(phoneNumber, text)" +
                "VALUES (?, ?)";

        mDatabase.execSQL(sql, new String []{phoneNumber, text});

        Toast.makeText(context,"contacts addedddddd",Toast.LENGTH_SHORT).show();
    }

}

这是我的SendActivity代码:

public class SendActivity extends AppCompatActivity {

    // define channel
    private static final String ChANNEL_ID = "simplified_coding";
    private static final String CHANNEL_NAME = "Simplified Coding";
    private static final String ChANNEL_DESC = "Simplified Coding Notification";


    Button sendBtn;
    Button sendBtn2;
    EditText phoneEditText;
    EditText plainEditText;

    MyDatabase MyDb;
    //    static TextView cipherTextView;
//    static TextView receivedTextview;

    static String pubKey="MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCJoBRPFYZb19vXqpiHzo2gPTq0" +
            "D1Ey++4PohVNboTBfsscUYA8SMPX4/Jz0NmhDbtk1PL3rqOVKubcEyJumxA+l46B" +
            "gNoQsnOBqXfE5Voo0GTbgP4AeN6MnkJ8mhawj3vu2TGmQqtlFYRyYbp6MZ6Q7ops" +
            "kZBKULJJJSwC9qSpewIDAQAB";
    static String privKey="MIICXAIBAAKBgQCJoBRPFYZb19vXqpiHzo2gPTq0D1Ey++4PohVNboTBfsscUYA8" +
            "SMPX4/Jz0NmhDbtk1PL3rqOVKubcEyJumxA+l46BgNoQsnOBqXfE5Voo0GTbgP4A" +
            "eN6MnkJ8mhawj3vu2TGmQqtlFYRyYbp6MZ6Q7opskZBKULJJJSwC9qSpewIDAQAB" +
            "AoGATMqdimMgTS7s5DG0WlLOg5KmpsHFNQWNl/uAl2wLd0wgWPTA8OJJJLV0G1t1" +
            "k3/uCB0qVTmE3T7LAhFLLRwou2wZbw3w48jF4uTXQJex6cf1xHVkXy6jBUVLlddW" +
            "74MQv3pfBRs/s0NsYML4J713r55JNmTU26WDwLA2xPNiosECQQDxAQQb7i1ZmSnr" +
            "9h0J6Ss3SGqpqDr/RRvUjSmCaCZtP/YFyNEd1aseQ8Wc31PpouwFgJbFYPEOAw+n" +
            "h2UECEiHAkEAkjBUvSFOFNnQIeiq1TUN/piEehSa8inLdU1psroVr09GprpS6nGZ" +
            "df66Nv0DhMCw6N1VjywnLNi8ru5zpg34bQJBAIXZWJzihRFT/XJtd+c/Np83evXK" +
            "1ylbCn/b/ofMrDrU4SCJTYrSVn0yipf7eLEzqP3NUu9ATeDIVnNmwPWiXBUCQGCL" +
            "PJs+8IMCqdqK/q8Zf6mA7hR1oTKGeZB5VHGtRP7m+wDHElU0OqXbWP1RsM4uN2dC" +
            "LOwFu8V5SXq5jXS/yy0CQCpkkZ6YEHxcKJGptVyAtC5iYNCun0pYNjrJHflu6ia8" +
            "pvX7FcJBo2l2Kmld6gXDlYnlJpyOSTapMDjSEs/DNr8=";



//    public static final String DATABASE_NAME = "contact_db" ;

    static SQLiteDatabase mDatabase;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_send );
        getWindow().getDecorView().setBackgroundColor(Color.rgb(249, 247, 209));
        MyDb = new MyDatabase(this);

        // Database Code
        mDatabase = openOrCreateDatabase(DATABASE_NAME, MODE_PRIVATE, null);

//        CREATE_TABLE();
        // handel android8 for channel

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(ChANNEL_ID, CHANNEL_NAME, NotificationManager.IMPORTANCE_DEFAULT);
            channel.setDescription(ChANNEL_DESC);
            NotificationManager notificationManager = getSystemService(NotificationManager.class);
            notificationManager.createNotificationChannel(channel);
        }


        Typeface face = Typeface.createFromAsset(getAssets(),
                "fonts/BRoya.ttf");

        phoneEditText = (EditText) findViewById(R.id.editTextPhoneNumber);
        plainEditText = (EditText) findViewById(R.id.editTextContent);
//        cipherTextView = (TextView) findViewById(R.id.textViewCipherText);
//        receivedTextview = (TextView) findViewById(R.id.textViewReceivedText);
        sendBtn = (Button) findViewById(R.id.buttonSendSMS);
        sendBtn2 = (Button) findViewById(R.id.buttonSendContacts);
        phoneEditText.setTypeface(face);
        plainEditText.setTypeface(face);
//        receivedTextview.setTypeface(face);
//        sendBtn.setTypeface(face);


    }

    public void gotoMessage(View view){

        switch (view.getId()) {

            case R.id.buttonSendContacts:

                startActivity(new Intent(this, MessageActivity .class));
                break;
        }


    }

    public void sendSMS(View V){
        try {

            String phoneNumber = phoneEditText.getText().toString();
            String plainText = plainEditText.getText().toString();
            String cipherText = encryptBeforeSend(plainText);
//            String decodedText = decryptAfterReceive(cipherText);
//            decodedText += "!!";
//            cipherTextView.setText(cipherText);
//            receivedTextview.setText(decodedText);

            if (ContextCompat.checkSelfPermission(SendActivity.this, Manifest.permission.SEND_SMS) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(SendActivity.this, new String[]{Manifest.permission.SEND_SMS}, 1);
            } else {
                SmsManager smsManager = SmsManager.getDefault();
                ArrayList<String> msgArray = smsManager.divideMessage(cipherText);

                smsManager.sendMultipartTextMessage(phoneNumber, null, msgArray, null, null);
                Toast.makeText(getApplicationContext(),
                        "SMS sent!",
                        Toast.LENGTH_LONG).show();
                MyDb.addContacts(phoneNumber, plainText, this);
            }
        }
        catch (Exception e) {
            Toast.makeText(getApplicationContext(),
                    "SMS faild, please try again later!"+e.toString(),
                    Toast.LENGTH_LONG).show();
            e.printStackTrace();
        }
    }

    public String encryptBeforeSend(String inputString) {
        // encrypt
        byte[] userData = inputString.getBytes();
        try {
            byte[] encodeData = myRSA.encryptByPublicKey(userData, pubKey);
//            String encodeStr = new BigInteger(1, encodeData).toString(16);
            String encodeStr = Base64.encodeToString(encodeData, Base64.DEFAULT);
            return encodeStr;
        }
        catch (Exception ex){
            ex.printStackTrace();
            return ex.toString();
        }

    }

}

当我调用 sendSMS 函数时，我收到数据库空对象引用错误，当我调用 gotoMessage 函数时，应用程序崩溃了，我知道原因是崩溃的是数据库。

有人可以帮我吗？

Answer 1

首先，由于拼写错误，在 onCreate() 内的 mDatabase.execSQL() 中传递的字符串不是有效的数据库查询 (INTEGEER) 以及字符串连接期间的错误间距。应该是:

@Override
public void onCreate(SQLiteDatabase mDatabase) {
    mDatabase.execSQL("CREATE TABLE " + TABLE_NAME + " (" + COL_1 + " INTEGER PRIMARY KEY, " + COL_2 + " VARCHAR, " + COL_3 + " VARCHAR)");
}

否则可能不会创建数据库表。

接下来，如官方所说documentation ,

getWritableDatabase() is used to create and/or open a database that will be used for reading and writing.

此外，根据 documentation ,

execSQL() executes a single SQL statement that is NOT a SELECT/INSERT/UPDATE/DELETE. For INSERT statements, use any of the following instead.

• insert(java.lang.String, java.lang.String, android.content.ContentValues)
• insertOrThrow(java.lang.String, java.lang.String, android.content.ContentValues)
• insertWithOnConflict(java.lang.String, java.lang.String, android.content.ContentValues, int)

因此，您的 addContacts() 方法应该如下所示:

public void addContacts(String phoneNumber, String text, Context context) {
    if (phoneNumber.isEmpty())
        return;

    SQLiteDatabase mDatabase = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put("phoneNumber", phoneNumber);
    values.put("text", text);

    mDatabase.insert("contact_msg", null, values);
    mDatabase.close();
    Toast.makeText(context, "contacts added", Toast.LENGTH_SHORT).show();
}