Santi Gil Santi Gil - 3 months ago 15
Android Question

Separate Back Navigation for a Tabbed View Pager in Android

What I want.

In a tab sliding menu context, I want to replace a fragment to another inside a tab, and maintaining the tab menu, and also the current tab. When sliding to another tab and returning to original, I want the last fragment to be displayed.

For example, I have

tab_a
with
Fragment_1
,
tab_b
with
Fragment_4
and
tab_c
with
Fragment_7
. Now I want a button in
Fragment_1
that opens me
Fragment_2
, but I want to be able to swipe to the fragments of the
tab_b
and
tab_c
. And when I return to tab_a,
Fragment_2
must be displayed.

enter image description here

MainActivity
|
|
ContainerFragment
|
|
|_ _ _ Tab A
| |_ _ _ Fragment 1
| |
| |_ _ _ Fragment 2
| |
| |_ _ _ Fragment 3
| |
| |_ _ _ ...
|
|_ _ _ Tab B
| |_ _ _ Fragment 4
| |
| |_ _ _ Fragment 5
| |
| |_ _ _ Fragment 6
| |
| |_ _ _ ...
|
|_ _ _ Tab C
| |_ _ _ Fragment 7
| |
| |_ _ _ Fragment 8
| |
| |_ _ _ Fragment 8
| |
| |_ _ _ ...


My current main activity.

Xml

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabMode="fixed"
app:tabGravity="fill"/>
</android.support.design.widget.AppBarLayout>

<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</android.support.design.widget.CoordinatorLayout>


Code

public class MainActivity extends AppCompatActivity {

private TabLayout tabLayout;

private final static int[] tabIcons = {
R.drawable.ic_tab_a,
R.drawable.ic_tab_b,
R.drawable.ic_tab_c
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);

tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
setupTabIcons();
}

private void setupTabIcons() {
tabLayout.getTabAt(0).setIcon(tabIcons[0]);
tabLayout.getTabAt(1).setIcon(tabIcons[1]);
tabLayout.getTabAt(2).setIcon(tabIcons[2]);
}

private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(new Fragment1());
adapter.addFrag(new Fragment4());
adapter.addFrag(new Fragment7());
viewPager.setAdapter(adapter);
}

class ViewPagerAdapter extends FragmentPagerAdapter {

private final List<Fragment> mFragmentList = new ArrayList<>();

ViewPagerAdapter(FragmentManager manager) {
super(manager);
}

@Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}

@Override
public int getCount() {
return mFragmentList.size();
}

void addFrag(Fragment fragment) {
mFragmentList.add(fragment);
}
}
}


Fragments

Xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:background="@android:color/holo_blue_light"
android:id="@+id/fragment_1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="myContext">

<Button
android:text="Go to next Fragment"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:id="@+id/button_nextFrag" />

<FrameLayout
android:id="@+id/tab1_container"
android:layout_width="match_parent"
android:layout_height="match_parent"/>

</RelativeLayout>


Code

public class Fragment1 extends Fragment {

private void goNextFragment() {
FragmentTransaction trans = getFragmentManager().beginTransaction();
trans.replace(R.id.tab1_container, new Fragment2());
trans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
trans.addToBackStack(null);
trans.commit();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment.
View root = inflater.inflate(R.layout.fragment_1, container, false);
// Go to next Fragment Button.
final Button nextFrag = (Button) root.findViewById(R.id.button_nextFrag);
nextFrag .setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
goNextFragment();
}
});
return root;
}
}


Edit:

I've got some solutions, but none is perfect. If I put a Framelayaout in MainActivity,
Fragment_1
is correctly replaced to
Fragment_2
, but it is also in
tab_b
and
tab_c
. If the FrameLayout is in
Fragment_1
, I can swipe the other tabs correctly, but the replacement goes not good, cause
Fragment_2
is opened, but
Fragment_1
is also there.

Answer

You can use a ViewPager together with a TabLayout.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<android.support.v4.view.ViewPager
    android:id="@+id/viewpager"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"/>
<android.support.design.widget.TabLayout
    android:id="@+id/tablayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>
</LinearLayout>

Then create a class that extends FragmentStatePagerAdapter to initialize the ViewPager with your initial Fragments:

public class CustomPagerAdapter extends FragmentStatePagerAdapter {
    private final List<String> tabTitles = new ArrayList<String>() {{
        add("Fragment 1");
        add("Fragment 4");
        add("Fragment 7");
    }};

    private List<Fragment> tabs = new ArrayList<>();

    public CustomPagerAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);

        initializeTabs();
    }

    private void initializeTabs() {
        tabs.add(HostFragment.newInstance(new Fragment1()));
        tabs.add(HostFragment.newInstance(new Fragment4()));
        tabs.add(HostFragment.newInstance(new Fragment7()));
    }

    @Override
    public Fragment getItem(int position) {
        return tabs.get(position);
    }

    @Override
    public int getCount() {
        return tabs.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles.get(position);
    }
}

The fragments containing the actual contents should be wrapped by a HostFragment, that uses its child FragmentManager to replace the current fragment with a new one if you want to navigate, or to pop the last fragment from the fragment stack. Call its replaceFragment to navigate:

public class HostFragment extends BackStackFragment {
    private Fragment fragment;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.host_fragment, container, false);
        if (fragment != null) {
            replaceFragment(fragment, false);
        }
        return view;
    }

    public void replaceFragment(Fragment fragment, boolean addToBackstack) {
        if (addToBackstack) {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).addToBackStack(null).commit();
        } else {
            getChildFragmentManager().beginTransaction().replace(R.id.hosted_fragment, fragment).commit();
        }
    }

    public static HostFragment newInstance(Fragment fragment) {
        HostFragment hostFragment = new HostFragment();
        hostFragment.fragment = fragment;
        return hostFragment;
    }
}

The HostFragment should extend the abstract class BackstackFragment

public abstract class BackStackFragment extends Fragment {
    public static boolean handleBackPressed(FragmentManager fm)
    {
        if(fm.getFragments() != null){
            for(Fragment frag : fm.getFragments()){
                if(frag != null && frag.isVisible() && frag instanceof BackStackFragment){
                    if(((BackStackFragment)frag).onBackPressed()){
                        return true;
                    }
                }
            }
        }
        return false;
    }

    protected boolean onBackPressed()
    {
        FragmentManager fm = getChildFragmentManager();
        if(handleBackPressed(fm)){
            return true;
        } else if(getUserVisibleHint() && fm.getBackStackEntryCount() > 0){
            fm.popBackStack();
            return true;
        }
        return false;
    }
}

Wire everthing up in the MainActivity:

public class MainActivity extends AppCompatActivity {
    private CustomPagerAdapter customPagerAdapter;
    private ViewPager viewPager;
    private TabLayout tabLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        tabLayout = (TabLayout) findViewById(R.id.tablayout);
        customPagerAdapter = new CustomPagerAdapter(getSupportFragmentManager());

        // 2 is enough for us; increase if you have more tabs!
        viewPager.setOffscreenPageLimit(2);
        viewPager.setAdapter(customPagerAdapter);
        tabLayout.setupWithViewPager(viewPager);
    }

    @Override
    public void onBackPressed()
    {
        if(!BackStackFragment.handleBackPressed(getSupportFragmentManager())){
            super.onBackPressed();
        }
    }

    public void openNextFragment() {
        HostFragment hostFragment = (HostFragment) customPagerAdapter.getItem(viewPager.getCurrentItem());

        // your logic to change the fragments...
    }
}

This solution is certainly not perfect but gets the job done. Read more fluff about it in my blog post on the issue.