最近初学android,做了实验室老师给的基本任务，就是简单的登陆和注册，并能通过SQLite实现登陆，SQlLite是嵌入在安卓设备中的

好了下面是主要代码：

数据库的建立：

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);
    }

}

注册：

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);