Use Tab layout in MVVM architecture with the data binding library

Question

I am developing an app that has a tab layout as the image.

I’d like to use MVVM architecture with data binding library but I am new with this framework.

Answer 1

MainActivity -

    public class MainActivity extends Activity 
    {
        @Override
        protected void onCreate(@Nullable final Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            App.get(this).component().inject(this);
            ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            binding.setHandler(this);
            binding.setManager(getSupportFragmentManager());
        }
        
        @BindingAdapter({"bind:handler"})
        public static void bindViewPagerAdapter(final ViewPager view, final MainActivity activity)
        {
            final MainActionsAdapter adapter = new MainActionsAdapter(view.getContext(), activity.getSupportFragmentManager());
            view.setAdapter(adapter);
        }
        
        @BindingAdapter({"bind:pager"})
        public static void bindViewPagerTabs(final TabLayout view, final ViewPager pagerView)
        {
            view.setupWithViewPager(pagerView, true);
        }
    
    }

xml -

    <layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:fresco="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">
    
        <data>
    
            <import type="android.view.View" />
    
            <variable
                name="handler"
                type="com.ui.main.MainActivity" />
    
            <variable
                name="manager"
                type="android.support.v4.app.FragmentManager" />
        </data>
    
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
    
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:animateLayoutChanges="true"
                app:title="@string/app_name"
                app:titleMarginStart="8dp" />
    
            <android.support.design.widget.TabLayout
                android:id="@+id/tab_layout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:pager="@{(pager)}">
            </android.support.design.widget.TabLayout>
    
            <android.support.v4.view.ViewPager
                android:id="@+id/pager"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:handler="@{handler}" />
    
        </LinearLayout>
    
    </layout>

Adapter -

    public class MainSectionsAdapter extends FragmentPagerAdapter
    {
        private static final int CONTACTS = 0;
        private static final int CALLS = 1;
        private static final int CHATS = 2;
        
        private static final int[] TABS = new int[]{CONTACTS, CALLS, CHATS};
        
        private Context mContext;
        
        public MainSectionsAdapter(final Context context, final FragmentManager fm)
        {
            super(fm);
            mContext = context.getApplicationContext();
        }
        
        @Override
        public Fragment getItem(int position)
        {
            switch (TABS[position])
            {
                case CONTACTS:
                    return ContactsFragment.newInstance();
                case CALLS:
                    return CallsFragment.newInstance();
                case CHATS:
                    return ChatsFragment.newInstance();
            }
            return null;
        }
        
        @Override
        public int getCount()
        {
            return TABS.length;
        }
        
        @Override
        public CharSequence getPageTitle(int position)
        {
            switch (TABS[position])
            {
                case CONTACTS:
                    return mContext.getResources().getString(R.string.contacts);
                case CALLS:
                    return mContext.getResources().getString(R.string.calls);
                case CHATS:
                    return mContext.getResources().getString(R.string.chats);
            }
            return null;
        }
    }

Answer 2

Here is my solution for setUpWithViewpager using databinding:

    public class BindingUtil
    {
        @BindingAdapter({ "setUpWithViewpager" })
        public static void setUpWithViewpager(final TabLayout tabLayout, ViewPager viewPager)
        {
            viewPager.addOnAdapterChangeListener(new ViewPager.OnAdapterChangeListener()
            {
                @Override
                public void onAdapterChanged(@NonNull ViewPager viewPager, @Nullable PagerAdapter oldAdapter, @Nullable PagerAdapter newAdapter)
                {
                    if (oldAdapter == null && (newAdapter == null || newAdapter.getCount() == 0))
                    {
                        // this function will helpful when 
                        // we don't create viewpager immediately 
                        // when view created (this mean we create
                        // will pager after a period time)
                        return;
                    }
                    tabLayout.setupWithViewPager(viewPager);
                }
            });
        }
    }

xml

<android.support.design.widget.TabLayout
     ... 
     app:setUpWithViewpager="@{ viewPager }"
/>

<android.support.v4.view.ViewPager
     ...
     android:id="@+id/viewPager"
     app:adapter="@{viewModel.pagerAdapter}"
/>

ViewModel

    public class MainViewModel extends BaseObservable
    {

        @Bindable
        public PagerAdapter getPagerAdapter()
        {
            return adapter;
        }

        private void createViewPagerAdapter()
        {
            ...
            notifyPropertyChanged(BR.pagerAdapter);
        }
    }

full demo project here

Hope it help

Answer 3

I'm not sure if this is newly introduced recently but with Android Support version 27.1.1, you don't even even need a custom data binding adapter, you can simply use:

<android.support.design.widget.TabLayout
                android:id="@+id/tl_1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:setupWithViewPager="@{some_fragment_viewpager}"
                app:tabSelectedTextColor="@android:color/white"
                app:tabTextColor="@color/v5_grey_55"
                />


        <android.support.v4.view.ViewPager
            android:id="@+id/some_fragment_viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:addOnPageChangeListener="@{vm.pageChangeListener}"
            app:setAdapter="@{vm.pageAdapter}"
            app:setCurrentItem="@{vm.pageChangeListener.currentPosition}"
            />

Take note that the viewPager variable in app:setupWithViewPager="@{some_fragment_viewpager}" points to android:id="@+id/some_fragment_viewpager". That's how the reference to the ViewPager is done (like magic I know)!

ViewModel

public class SomeViewModel {
  public ViewPager.OnPageChangeListener pageChangeListener;
  public SomeFragmentPagerAdapter pagerAdapter;
  // ...
}

FragmentPagerAdapter

public classs SomeFragmentPagerAdapter extends FragmentPagerAdapter {
  public Boolean currentPosition;
}