从交互器传递字符串资源以在android MVP中查看

Question

So, I am currently trying to implement MVP approach in android, which I am new to. Now, it states that neither presenter nor the interactor class should have knowledge about android classes or components.

Makes sense to decouple the business logic from framework. Good so far.

However I have an presenter that implements a callback to login in interactor, that passes a string resource id. The presenter passes the string res id to the view that displays error message in some form (whether a toast or a dialog).

Interactor:

public interface SignInteractor {

void login(String email, String password, OnLoginListener loginListener);

interface OnLoginListener {

    void onLoginSuccess();

    void onLoginFail(int error);

   } 
}

Presenter:

public interface SignInPresenterImpl {
private SignInteractorImpl mInteractor; // interactor implementation
private SignInView mSignInView; // view reference

// additional code 

    void login(String email, String password){

        mInteractor.login(email,password, new SignInteractor.OnLoginListener(){

        @Override
        public void onLoginSuccess() {
            if (mSignInView != null) {
                mSignInView.signInSuccess();
            }
        }

        @Override
        public void onLoginFail(final int error) {
            if (mSignInView != null) {
                mSignInView.showError(R.string.error);
            }
        }
        })
    }

}

Activity View:

SignInViewActivity implements SignInView{
   // additional code

   void showError(int resId){
    Toast.makeText(this, getString(resId), Toast.LENGTH_SHORT).show();
   }
}

However, since R file is a part of android framework, this renders the presenter and interactor to not be usable in pure java apps.

I have gone through a lot of articles and discussions on various forums which provide various ways to achieve this.

Solutions :

1. view should use method like showLoginError() and decide itself how handle the view logic. In this way presenter has no knowledge of android related stuff.

   • However, string manipulation from interactor is not possible.

2. Create specific methods in view handling all cases eg showinvalidEmail(), showinvalidPassword() etc.

   • too many methods, difficult in complex cases.

3. using enum for error type and passing to view view.showError(ErrorTypes.INVALID_EMAIL) -still confused about #enumsmatter :)

https://www.reddit.com/r/androiddev/comments/4v4urs/mvp_question_how_do_you_populate_your_textviews/

4. Use a resource abstraction or wrapper class that provides the required string.
   • difficult when there are large number of strings to be used.

https://medium.com/@daptronic/android-mvp-the-curious-case-of-resources-ddca39c1fccd

5. use library that provides api implementation for each string in strings.xml
   • still in beta stage

https://github.com/Comcast/resourceprovider

Please suggest what is the best approach to attain this as to not violate the principles of mvp or clean architecture.

Answer 1

As you already now which error you like to display when login failure so you just need to remove parameter from showError declaration and try to call that method from presenter without any parameter and view will be taking care of which message display when this showError function called as below :

View

void showError(){
    Toast.makeText(this, getString(R.string.error), Toast.LENGTH_SHORT).show();
}

Presenter

mSignInView.showError();

And also define one more method to shown error from response as below :

View

void showError(String error){
    Toast.makeText(this, error, Toast.LENGTH_SHORT).show();
}

Presenter

mSignInView.showError(error);

Answer 2

In my understandings MVP is not about taking away the android class from your business logic, but about separating the logic and UI part, and accessing an android class or resources from interactor is not a mistake.

But if you want to separate completely, ie all android resources or classes from interactor then supply the type and read it from UI.

SignInViewActivity implements SignInView{
// additional code

    void showError(int errorType){
         switch(errorType){
             case ....:
         }
         //display message
    }
}

Answer 3

you can create an enumeration class like

 enum class AuthError {
        INPUT_EMAIL_INVALID,
        INPUT_PASSWORD_INVALID,
        RESPONSE_EMAIL_DOES_NOT_EXIST
 }

Then you can pass it to view like this

AuthView.someError(AuthError.INPUT_EMAIL_INVALID)

You can check the type of the error by checking the type of the AuthError from there you can call R.string.error_message

This would remove the Presenter with Android Specific code.