致命例外：Android SQLite 上的主要功能

Question

嗨，我是 android 新手，这是我第一次使用 sqlite，当我尝试添加或从数据库中读取时，我不断收到致命异常：main。

Signup.java

Signup.java是主Activity调用的Activity

public class Signup extends Activity

{

MySQLiteHelper db = new MySQLiteHelper(this);

public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.signup);  
}

public void onClick(View v)
{
    TextView user = (TextView) findViewById(R.id.EUser); 
    TextView pass = (TextView) findViewById(R.id.EPass);
    TextView conpass = (TextView) findViewById(R.id.ConEPass);

    String userid = user.getText().toString();
    String password = pass.getText().toString();
    String confirmpass = conpass.getText().toString();

    if(userid.equals("") || password.equals("") || confirmpass.equals(""))
    {
        Toast.makeText(getApplicationContext(), "Please enter all fields",
                Toast.LENGTH_LONG).show();
        user.setText("");
        pass.setText("");
        conpass.setText("");
    }   
    else if(!password.equals(confirmpass)){
        Toast.makeText(getApplicationContext(), "Passwords don't match, please enter again",
                Toast.LENGTH_LONG).show();
        pass.setText("");
        conpass.setText("");
    }
    else if(!db.getUserId(userid)){
        Toast.makeText(getApplicationContext(), "user id alreddy exists, please enter a new one",
                Toast.LENGTH_LONG).show();
        user.setText("");
    }
    else{
        Toast.makeText(getApplicationContext(), "Signing up ..............",
                Toast.LENGTH_LONG).show();
        db.insertUser(userid,password);
        Intent i = new Intent(Signup.this, MainActivity.class);
        startActivity(i);
    }
}
}

MySQLiteHelper.java:-

public class MySQLiteHelper{

private static final String LOGCAT = null;  

private static final int DATABASE_VERSION = 1;

private static final String DATABASE_NAME = "User.db";

private static final String DATABASE_USERS = "Users";

private static final String KEY_USERID = "userid";

private static final String KEY_PASSWORD = "password";

private static final String[] COLUMNS = {KEY_USERID,KEY_PASSWORD};

private static final String TABLE_USERS = "create table "+DATABASE_USERS+" (userid TEXT, password TEXT)";

private SQLiteDatabase SQLdb;

private HelperClass helper;

private final Context mContext;

public MySQLiteHelper(Context context){
    this.mContext=context;
    helper = new HelperClass(mContext);
}

public class HelperClass extends SQLiteOpenHelper{
    public HelperClass(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase SQLdb){
        try{
            SQLdb.execSQL(TABLE_USERS);
            Log.d(LOGCAT, "Table Created");
        }
        catch(SQLException e){

        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase SQLdb, int oldVersion, int newVersion){
        SQLdb.execSQL("DROP TABLE IF EXISTS Users");
        Log.d(LOGCAT,"Table being recreated");
        onCreate(SQLdb);
    }
}

public MySQLiteHelper open(){
    Log.d(LOGCAT, "trying to open");
    SQLdb = helper.getWritableDatabase();
    return this;
}

public void close(){
    helper.close();
}

public void insertUser(String Userid,String Password){
    ContentValues values = new ContentValues();
    values.put(KEY_USERID,Userid);
    values.put(KEY_PASSWORD, Password);
    open();
    SQLdb.insert(DATABASE_USERS,null,values);
    close();
    Log.d(LOGCAT, "Inserted User");
}

public boolean getUserId(String userid){
    open();
    Cursor cursor = SQLdb.query(true,DATABASE_USERS,COLUMNS,KEY_USERID+"="+userid,null,null,null,null,null);//log shows as error
    close();
    if(cursor!=null){
        Log.d(LOGCAT, "Found userid in DB");
        return true;
    }
    else{
        Log.d(LOGCAT, "Userid not found in DB");
        return false;
    }
}

public boolean getPassword(String password){
    open();
    Cursor cursor = SQLdb.query(true,DATABASE_USERS,COLUMNS,KEY_PASSWORD+"="+password,null,null,null,null,null);
    if(cursor!=null){
        Log.d(LOGCAT, "Found password in DB");
        return true;
    }
    else{
        Log.d(LOGCAT, "Password not found in DB");
        return false;
    }
}
}

这些是日志

01-24 16:46:19.024: E/SQLiteLog(12259): (1) 没有这样的列: lxnv 01-24 16:46:19.034：E/AndroidRuntime（12259）：致命异常：主要 01-24 16:46:19.034: E/AndroidRuntime(12259): 进程: com.lxnv.myfirstapp, PID: 12259 01-24 16:46:19.034: E/AndroidRuntime(12259): java.lang.IllegalStateException: 无法执行活动的方法 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.view.View$1.onClick(View.java:3823) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.view.View.performClick(View.java:4438) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.view.View$PerformClick.run(View.java:18422) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.os.Handler.handleCallback(Handler.java:733) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.os.Handler.dispatchMessage(Handler.java:95) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.os.Looper.loop(Looper.java:136) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.app.ActivityThread.main(ActivityThread.java:5017) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 java.lang.reflect.Method.invokeNative(Native Method) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 java.lang.reflect.Method.invoke(Method.java:515) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 01-24 16:46:19.034: E/AndroidRuntime(12259): at dalvik.system.NativeStart.main(Native Method) 01-24 16:46:19.034: E/AndroidRuntime(12259): 由: java.lang.reflect.InvocationTargetException 引起 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 java.lang.reflect.Method.invokeNative(Native Method) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 java.lang.reflect.Method.invoke(Method.java:515) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.view.View$1.onClick(View.java:3818) 01-24 16:46:19.034: E/AndroidRuntime(12259): ... 11 更多 01-24 16:46:19.034: E/AndroidRuntime(12259): 由: android.database.sqlite.SQLiteException: 没有这样的列: lxnv(code 1): , 编译时: SELECT DISTINCT userid, password FROM Users WHERE userid =lxnv 01-24 16:46:19.034：E/AndroidRuntime（12259）：在 android.database.sqlite.SQLiteConnection.nativePrepareStatement（本机方法） 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteProgram.(SQLiteProgram.java:58) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteQuery.(SQLiteQuery.java:37) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1161) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1032) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 com.lxnv.myfirstapp.MySQLiteHelper.getUserId(MySQLiteHelper.java:76) 01-24 16:46:19.034: E/AndroidRuntime(12259): 在 com.lxnv.myfirstapp.Signup.onClick(Signup.java:43) 01-24 16:46:19.034: E/AndroidRuntime(12259): ... 14 更多

Answer 1

MySQLiteHelper db = new MySQLiteHelper(null); 在这一行你不能将上下文作为null 传递。

所以替换这个

MySQLiteHelper db = new MySQLiteHelper(null);

有了这个

MySQLiteHelper db ;

并在OnCreate() .. 中初始化它。

db = new MySQLiteHelper(this);

Answer 2

试试

SQLdb = getWritableDatabase();

在您的 insertUser() 方法中。