android简单登陆和注册功能实现+SQLite数据库学习

这里我只是建立了一个用简单的存储用户名和密码的表单

MyDBHelper.java

public class MyDBHelper extends SQLiteOpenHelper {        public static final String CREATE_USERDATA="create table userData(" +            "id integer primary key autoincrement,"            +"nametext,"            +"password text)";    private Context mContext;    public MyDBHelper(Context context, String name, SQLiteDatabase.CursorFactory cursorFactory,int version){        super(context,name,cursorFactory,version);        mContext=context;    }    public  void onCreate(SQLiteDatabase db){        db.execSQL(CREATE_USERDATA);    }    public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){        //onCreate(db);    }}

Main2Activity.java

public class Main2Activity extends AppCompatActivity {    private MyDBHelper dbHelper;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main2);        dbHelper = new MyDBHelper(this,"UserStore.db",null,1);    }    public void logon(View view){        //SQLiteDatabase db=dbHelper.getWritableDatabase();        EditText editText3=(EditText)findViewById(R.id.editText3);        EditText editText4=(EditText)findViewById(R.id.editText4);        String newname =editText3.getText().toString();        String password=editText4.getText().toString();        if (CheckIsDataAlreadyInDBorNot(newname)) {            Toast.makeText(this,"该用户名已被注册，注册失败",Toast.LENGTH_SHORT).show();        }        else {            if (register(newname, password)) {                Toast.makeText(this, "插入数据表成功", Toast.LENGTH_SHORT).show();            }        }    }//向数据库插入数据    public boolean register(String username,String password){        SQLiteDatabase db= dbHelper.getWritableDatabase();        /*String sql = "insert into userData(name,password) value(?,?)";        Object obj[]={username,password};        db.execSQL(sql,obj);*/        ContentValues values=new ContentValues();        values.put("name",username);        values.put("password",password);        db.insert("userData",null,values);        db.close();        //db.execSQL("insert into userData (name,password) values (?,?)",new String[]{username,password});        return true;    }//检验用户名是否已存在    public boolean CheckIsDataAlreadyInDBorNot(String value){        SQLiteDatabase db=dbHelper.getWritableDatabase();        String Query = "Select * from userData where name =?";        Cursor cursor = db.rawQuery(Query,new String[] { value });        if (cursor.getCount()>0){            cursor.close();            return  true;        }        cursor.close();        return false;    }}

登陆：

MainActivity.java

public class MainActivity extends AppCompatActivity {    private MyDBHelper dbHelper;    private EditText username;    private EditText userpassword;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        //requestWindowFeature(Window.FEATURE_NO_TITLE);        setContentView(R.layout.activity_main);                dbHelper = new MyDBHelper(this,"UserStore.db",null,1);    }         //点击注册按钮进入注册页面    public void logonClicked(View view){        Intent intent = new Intent(MainActivity.this,Main2Activity.class);        startActivity(intent);    }    //点击登录按钮    public void loginClicked(View view) {        username=(EditText)findViewById(R.id.editText2);        userpassword=(EditText)findViewById(R.id.editText);        String userName=username.getText().toString();        String passWord=userpassword.getText().toString();        if (login(userName,passWord)) {            Toast.makeText(MainActivity.this, "登陆成功（ZY，111）", Toast.LENGTH_SHORT).show();        }        else {            Toast.makeText(MainActivity.this, "登陆失败", Toast.LENGTH_SHORT).show();        }    }    //验证登录    public boolean login(String username,String password) {        SQLiteDatabase db = dbHelper.getWritableDatabase();        String sql = "select * from userData where name=? and password=?";        Cursor cursor = db.rawQuery(sql, new String[] {username, password});        if (cursor.moveToFirst()) {            cursor.close();            return true;        }        return false;    }

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