将数据插入Android SQLITE数据库时，空指针异常

Question

我刚刚启动一个Android Studio项目，而IVE创建了一个小玩家数据库，我一直在尝试将播放器详细信息添加到数据库中。但是，每次程序都以空指针异常崩溃。一个快速的调试表明，问题是在ongreate方法中呼叫OnClickListener的问题。代码需要进行哪些更改？谢谢

public class DatabaseHelper {
    // Declare instance of DBHelper class, context and SQLiteDatabase
    private DBHelper ourDbHelper;
    private final Context ourContext;
    private SQLiteDatabase myDb;
    // Initialise the database and table names and version
    private static final String DATABASE_NAME = "Club";
    private static final String PLAYER_TABLE_NAME = "Players";
    //Initialise the PLAYER_TABLE_NAME field names
    private static final String PLAYER_ID = "player_id";
    private static final String PLAYER_SURNAME = "player_surname";
    private static final String PLAYER_FORENAME = "player_forename";
    private static final String PLAYER_AGE = "player_age";
    private static final String PLAYER_DOB = "player_dob";
     private static class DBHelper extends SQLiteOpenHelper {

        // This constructor takes the context, db name and db version as 
    parameters
        // and applies them to the DBHelper class
        public DBHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        // This constructor takes context as parameter and assigns it to 
    variable
        @Override
        public void onCreate(SQLiteDatabase db) {
            //Executes the following queries to create the Player Table
            db.execSQL("CREATE TABLE " + PLAYER_TABLE_NAME + " (" + PLAYER_ID 
    + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                    + PLAYER_FORENAME + "TEXT NOT NULL, " + PLAYER_SURNAME + 
    "TEXT NOT NULL, " +
                    PLAYER_AGE + " INTEGER NOT NULL, " + PLAYER_DOB + "DATE 
    NOT NULL );");
        }//OnCreate
    @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int 
    newVersion) {
            // if table is upgraded or already exists
            db.execSQL("DROP TABLE IF EXISTS " + PLAYER_TABLE_NAME);
            onCreate(db);
        }//OnUpgrade
    }//DBHelperClass
    // Constructor takes a context as a parameter and assigns it to 
    ourContext
    public DatabaseHelper (Context c){
        ourContext = c;
    }//constructor
    // Open writable database and allow to be modified
    public DatabaseHelper open() throws SQLException {
        ourDbHelper = new DBHelper(ourContext);
        myDb = ourDbHelper.getWritableDatabase();
        return this;
    }//open
    //method to close the db to modification
    public void close() {
        ourDbHelper.close();
    }//close
    // method to create an entry to the Player table with player attributes as parameters
    public long createEntry (String forename, String surname, String age, String dob){
        //contentValues will hold the information to be added to the database
        ContentValues contentValues = new ContentValues();
        //Using put method, insert the parameters into the fields in the table
        contentValues.put(PLAYER_FORENAME, forename);
        contentValues.put(PLAYER_SURNAME, surname);
        contentValues.put(PLAYER_AGE,age);
        contentValues.put(PLAYER_DOB, String.valueOf(dob));
        //insert the values into the player table
        //assign to variable result to check if data added correctly
        return myDb.insert(PLAYER_TABLE_NAME,null,contentValues);
    }//createEntry

这是AddPlayer Activity类

public class AddPlayer extends Activity implements View.OnClickListener {
    //declare variables
    Button confirmAdd;
    EditText editSurname, editForename, editAge, editDOB;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.add_player_activity);
        //Initialise variables
        editForename = (EditText) findViewById(R.id.editPlayerForename);
        editSurname = (EditText) findViewById(R.id.editPlayerSurname);
        editAge = (EditText) findViewById(R.id.editPlayerAge);
        editDOB = (EditText) findViewById(R.id.editPlayerDOB);
        confirmAdd = (Button) findViewById(R.id.addPlayerBtn);
        //set onclicklisteners
        confirmAdd.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {

        String forename = editForename.getText().toString();
        String surname = editSurname.getText().toString();
        String age = editAge.getText().toString();
        String dob = editDOB.getText().toString();
        DatabaseHelper myDb = new DatabaseHelper(AddPlayer.this);
        myDb.open();
        myDb.createEntry(forename, surname, age, dob);

        Toast.makeText(AddPlayer.this, "Data Inserted", Toast.LENGTH_LONG).show();
    }

Answer 1

更改此

DatabaseHelper myDb = new DatabaseHelper(AddPlayer.this);
myDb.open()

DatabaseHelper myDb = new DatabaseHelper(this.getContext());
myDb.open();