【架构】MVP模型

public interface LoginInteractor {
    void login(String userName,String password,OnLoginFinishedListener listener);
}

public interface LoginPresenter {
    void validateCredentials(String userName,String password);
    void onDestroy();
}

public interface OnLoginFinishedListener {
    void onUserNameError();
    void onPasswordError();
    void onSuccess();
}

public interface LoginView {
    void setUserNameError();
    void setPasswordError();
    void navigateToHome();
}

public class LoginInteractorImpl implements LoginInteractor {
    @Override
    public void login(final String userName, final String password, final OnLoginFinishedListener listener) {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Log.i("ZhiXueHui", "LoginInteractorImpl-login");
                boolean error = false;
                if(TextUtils.isEmpty(userName)){
                    listener.onUserNameError();
                    error = true;
                }
                if(TextUtils.isEmpty(password)){
                    listener.onPasswordError();
                    error = true;
                }
                if(!error){
                    listener.onSuccess();
                }
            }
        },2000);
    }
}

public class LoginPresenterImpl implements LoginPresenter,OnLoginFinishedListener {
    private LoginView loginView;
    private LoginInteractor loginInteractor;

    public LoginPresenterImpl(LoginView loginView){
        this.loginView = loginView;
        this.loginInteractor = new LoginInteractorImpl();
    }

    @Override
    public void validateCredentials(String userName, String password) {
        Log.i("ZhiXueHui", "LoginPresenterImpl-validateCredentials");
        loginInteractor.login(userName,password,this);
    }


    @Override
    public void onDestroy() {
        Log.i("ZhiXueHui", "LoginPresenterImpl-onDestroy");
        loginView = null;
    }

    @Override
    public void onUserNameError() {
        Log.i("ZhiXueHui", "LoginPresenterImpl-onUserNameError");
        if(loginView!=null){
            loginView.setUserNameError();
        }
    }

    @Override
    public void onPasswordError() {
        Log.i("ZhiXueHui", "LoginPresenterImpl-onPasswordError");
        if(loginView!=null){
            loginView.setPasswordError();
        }
    }

    @Override
    public void onSuccess() {
        Log.i("ZhiXueHui", "LoginPresenterImpl-onSuccess");
        if(loginView!=null){
            loginView.navigateToHome();
        }
    }
}

public class LoginActivity extends Activity implements LoginView, View.OnClickListener {

    private EditText userName;
    private EditText password;
    private Button button;
    private LoginPresenter presenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        Log.i("ZhiXueHui", "LoginActivity-onCreate");
        userName = (EditText) findViewById(R.id.userName);
        password = (EditText) findViewById(R.id.password);
        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(this);

        presenter = new LoginPresenterImpl(this);
    }

    @Override
    public void setUserNameError() {
        Log.i("ZhiXueHui", "LoginActivity-setUserNameError");
        userName.setError(getString(R.string.username_error));
    }

    @Override
    public void setPasswordError() {
        Log.i("ZhiXueHui", "LoginActivity-setPasswordError");
        password.setError(getString(R.string.password_error));
    }

    @Override
    public void navigateToHome() {
        Log.i("ZhiXueHui", "LoginActivity-navigateToHome");
        startActivity(new Intent(this, MainActivity.class));
        finish();
    }

    @Override
    public void onClick(View v) {
        Log.i("ZhiXueHui", "LoginActivity-onClick");
        presenter.validateCredentials(userName.getText().toString(),password.getText().toString());
    }
}