登录使用Retrofit无法正常工作

Question

我正在通过改造创建用户登录但我无法从服务器（）mysql获取用户名和密码..我不知道我做错了什么。 接口

public interface LoginApi {
            @FormUrlEncoded
            @POST("/zaala/retrofitlogin.php")
            public void getlogin(
            @Field("username") String username,
            @Field("password")String password,
            Callback response
            );

MainActivity

 private static final String ROOT_LOGIN = "http://xxxxx.com";
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_login);

                editTextUsername = (EditText) findViewById(R.id.editTextUsername);
                editTextPassword = (EditText) findViewById(R.id.editTextPassword);

                buttonlogin = (Button) findViewById(R.id.buttonlogin);
                buttonlogin.setOnClickListener(this);

                restAdapter = new RestAdapter.Builder().setEndpoint(ROOT_LOGIN).build();
                restAdapter.setLogLevel(RestAdapter.LogLevel.FULL);
                loginApi = restAdapter.create(LoginApi.class);
            }
            @Override
            public void onClick(View v) {
           loginApi.getlogin(editTextUsername.getText().toString(), editTextPassword.getText().toString(), new Callback<String>() {
               @Override
               public void success(String s, Response response) {
                   Toast.makeText(LoginActivity.this,"Logged in",Toast.LENGTH_LONG).show();
               }
               @Override
               public void failure(RetrofitError error) {
                   Toast.makeText(LoginActivity.this,"Logged Failed",Toast.LENGTH_LONG).show();
               }
           });
            }

帮助---我使用的是php代码