在写完MVP模式（一）后，总觉得难以理解，并且感觉不应该在model层操作业务逻辑
下面同样以用户登陆为例，把model的业务实现交给Presenter操作

创建model

public class UserInfo {

    public String account;
    public String pwd;
}

创建view与model逻辑实现Presenter的接口

public class UserLoginApi {
  //view接收结果
    public interface View{
        void onLoginStar();
        void onLoginEnd();
        void onSuccess();
        void onFail();
    }
//model的逻辑实现，交给Presenter
    public interface Presenter {
        void login();
    }

}

创建Presenter实现登陆用户，并把结果返回给view

public class UserLoginPresenter implements UserLoginApi.Presenter {

    private UserLoginApi.View view;
    private UserInfo userInfo;

    public UserLoginPresenter(UserLoginApi.View view,UserInfo userInfo){
        this.view = view;
        this.userInfo = userInfo;
    }

    @Override
    public void login() {
        //模拟登陆
        new Handler().postDelayed(new Runnable() {

            @Override
            public void run() {
                view.onLoginStar();
                if (TextUtils.isEmpty(userInfo.account)||TextUtils.isEmpty(userInfo.pwd)){
                    return;
                }
                int i =new Random().nextInt(1);
                if (i==0){
                    view.onSuccess();
                    view.onLoginEnd();
                }else {
                    view.onFail();
                    view.onLoginEnd();
                }

            }
        },2000L);
    }
}

View层

public class LoginActivity extends Activity implements UserLoginApi.View{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        new UserLoginPresenter(this,new UserInfo()).login();
    }

    @Override
    public void onLoginStar() {

    }

    @Override
    public void onLoginEnd() {

    }

    @Override
    public void onSuccess() {

    }

    @Override
    public void onFail() {

    }
}