ViewPager's PagerAdapter & Mortar's Screens

[ksloginov]

Hi,

This topic has been discussed a while ago and even nice snippet has been posted (https://gist.github.com/kboyarshinov/d30c354541f95ecaeaac), but since then, the Flow and Mortar have changed and I'm a bit confused.

It used to be something like this:

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
    Path screen = screens[position];
        MortarScope originalScope = MortarScope.getScope(context);
        MortarScope newChildScope =  originalScope.requireChild(screen);
        Context childContext = newChildScope.createContext(context);
        View newChild = Layouts.createView(childContext, screen);
        container.addView(newChild);
        return newChild;
    }

But now, Layouts is no longer part of Flow and requireChild is no longer part of MortarScope.

Does anyone succeed in adapting it for the latest libs versions?

Thanks a lot(all square libraries are so awesome!) & best wishes!

[ksloginov]

Ok, I didn't succeed but, probably someone can guide me from this point:

The initial Dagger Registration:

@Module(
        injects = {
                MainActivity.class,
        },
        library = true,
        complete = false
)
public class DaggerConfig {
    @SuppressWarnings("unused")
    @Provides @Singleton Gson provideGson() {
        return new GsonBuilder().create();
    }
}

MainScreen, whose View is hosting ViewPager:

@Layout(R.layout.screen_main) @WithModule(MainScreen.Module.class)
public class MainScreen extends Path {
    @dagger.Module(injects = MainView.class, addsTo = DaggerConfig.class)
    public static class Module {}

    @Singleton
    public static class Presenter extends ViewPresenter<MainView> {
        @Inject
        public Presenter() {}
    }
}

MainView:

...........
    @Inject
    MainScreen.Presenter presenter;
...........
    @Override protected void onFinishInflate() {
        super.onFinishInflate();
        ButterKnife.inject(this);

        final Path[] screens = {
                new SubScreen("1"),
                new SubScreen("2"),
                new SubScreen("3"),
        };

        CustomPagerAdapter customPagerAdapter = new CustomPagerAdapter(getContext(), screens );
        customPagerAdapter .setAdapter(firstRunPagerAdapter);
    }
.....

Now, the main part, SubScreen (3 similar screens, that differs only by the parameters we are passing into them => they should adjust views according these parameters)

@Layout(R.layout.screen_subscreen) @WithModule(SubScreen.Module.class)
public class SubScreen extends Path {

    private final String title;

    public SubScreen(String titleParam) {
        title = titleParam;
    }

    @dagger.Module(injects = SubView.class, addsTo = DaggerConfig.class)
    public class Module {

        @Provides
        SubViewMetadata provideSubViewMetadata() {
            return new SubViewMetadata(backgroundColor, title);
        }

    }

    @Singleton
    public static class Presenter extends ViewPresenter<SubView> {

        private String title;

        @Inject
        public Presenter(String title) {
            this.title= title;
        }

        @Override
        protected void onLoad(Bundle savedInstanceState) {
            super.onLoad(savedInstanceState);
            if (!hasView()) {
                return;
            }

            getView().setTitle(subViewMetadata.title);
        }
    }
}

and it's view

public class SubView extends FrameLayout {

    @InjectView(R.id.subViewTitleTextView)
    TextView subViewTitleTextView;

    @Inject
    SubScreen.Presenter presenter;

    public SubView(Context context, AttributeSet attrs) {
        super(context, attrs);
        ObjectGraphService.inject(context, this);
    }

    public void setTitle(String title) {
        subViewTitleTextView.setText(title);
    }

    @Override protected void onAttachedToWindow() {....}

    @Override protected void onDetachedFromWindow() {....}
......
}

Custom Pager adapter:

public class CustomPagerAdapter extends PagerAdapter {

    private final Context context;
    private final Path[] screens;

    public CustomPagerAdapter(Context context, Path[] screens) {
        this.context = context;
        this.screens = screens;
    }

    @Override
    public int getCount() {
        return (screens == null)? 0 : screens.length;
    }

    @Override
    public boolean isViewFromObject(View view, Object o) {
        return view.equals(o);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {

        Path screen = screens[position];
        MortarScope originalScope = MortarScope.getScope(context);
        MortarScope newChildScope =  originalScope.buildChild().build("tutorialpage" + (new Random()).nextInt(999999));
        Context childContext = newChildScope.createContext(context);
        View newChild = Layouts.createView(childContext, screen);

        container.addView(newChild);
        return newChild;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        View view = ((View) object);
        container.removeView(view);
        MortarScope.getScope(view.getContext()).destroy();
    }
}

The problem statement: it's crashing, as SubView class hasn't been added into list of Injections at the "Layouts.createView(childContext, screen);" moment in the Adapter, and I can't add it by default, because I want to have a @Provider of data from SubScreen to SubScreen.Presenter. (I'm using local variable.

If I add SubView.class into list of injections and convert local Screen's variables into static, then I'll have 3 identical pages inside the ViewPager (which is logical, as every next call of the constructor - overrides old static variables).

Any help/ideas?

Thanks

[ksloginov]

Ok, apparently I did something.

First of all, adding SubView into list of globally injected classes. Then modifying SubScreen class:

@Layout(R.layout.screen_subscreen)
public class SubScreen extends Path {
    private static String titleStatic; // Introducing static variable
    private final String title;
    public SubScreen(String titleParam) {
        title = titleParam;
    }

    public void refreshPresenter() {
        titleStatic = title;
    }

    @Singleton
    public static class Presenter extends ViewPresenter<SubView> {

        private String title;

        @Inject
        public Presenter() {
        }

        @Override
        protected void onLoad(Bundle savedInstanceState) {
            super.onLoad(savedInstanceState);
            if (!hasView()) {
                return;
            }

            getView().setTitle(titleStatic);
        }
    }
}

and then in Custom adapter do this changes:

public class CustomPagerAdapter extends PagerAdapter {
    private final Context context;
    private final SubScreen[] screens;

    public CustomPagerAdapter(Context context, SubScreen[] screens) {
        this.context = context;
        this.screens = screens;
    }
    ......
    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        SubScreen screen = screens[position];
        MortarScope originalScope = MortarScope.getScope(context);
        MortarScope newChildScope =  originalScope.buildChild().build("tutorialpage" + position);
        Context childContext = newChildScope.createContext(context);

        screen.refreshPresenter(); // updating the static var with local one!

        View newChild = Layouts.createView(childContext, screen);
        container.addView(newChild);
        return newChild;
    }
    ....
}

I.e. the idea is to keep the local AND static variables in the Screen, if the same screen is going to be reused. And when we inflate the view it - just setting the right value to the static one (that would be used in the Presenter).

It works, though I'm not sure if it's a right way to do it, so would be very happy, if someone can approve this approach or propose a better solution.

[lukaspili]

In my opinion, your logic of static variable and refreshPresenter() looks wrong.
See here for an up to date example of view pager with Mortar and Flow: https://github.com/lukaspili/Mortar-Flow-Dagger2-demo
In particular, look at the following classes: SlidesScreen, SlidePageScreen, SlidePagerAdapter.

And in the future, you should use stack overflow for such topic.

[vsumtsov-gh]

At this gist, you can find above solution but with save state functionality.
https://gist.github.com/VladSumtsov/2128e0cc0f7c2131c0f971ee26d36ce5