Tabs of Tab Layout don't display anything

问题

This code is to create 3 tabs, made from fragments, that contains an image and text explanation, each one of them, to it. There's an obstacle on which the tabs don't display anything at all, all 3 of them. Here is the main code :

public class Cookings extends AppCompatActivity {

    private TabLayout tabLayout;
    private ViewPager viewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cookings);
        tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        viewPager = (ViewPager) findViewById(R.id.viewpager-id);

        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.AddFragment(new FragmentRoastedMeat(), "Roasted Meat");
        adapter.AddFragment(new FragmentStirFryVeggies(), "Stir-fry Vegetables");
        adapter.AddFragment(new FragmentBakedFish(), "Baked Fish");

        viewPager.setAdapter(adapter);
        tabLayout.setupWithViewPager(viewPager);

    }
}

and here is the view pager adapter class' code :

public class ViewPagerAdapter extends FragmentPagerAdapter {

   private final List<Fragment> fragmentList = new ArrayList<>();
   private final List<String> fragmentListTitles = new ArrayList<>();


   public ViewPagerAdapter(@NonNull FragmentManager fm) {
        super(fm);
    }

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

    @NonNull
    @Override
    public Fragment getItem(int position) {

       return fragmentList.get(position);

    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }
    public void AddFragment(Fragment fragment, String Title){
       fragmentList.add(fragment);
       fragmentListTitles.add(Title);
    }
}

There are two key things I'd like to fix here :

1. The deprecation on super(fm) function part on the main constructor of ViewPagerAdapter class, and
2. The tabs on the main tab layout that don't show any fragments I've made.

Any help would be appreciated.

回答1:

For deprecation fix, You need to add behavior in your ViewPagerAdapter like this:

import androidx.fragment.app.FragmentStatePagerAdapter;
     ....
     public ViewPagerAdapter(@NonNull FragmentManager fm) {
            super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
        }

Try using the code below:

Layout

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    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.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <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>

Activity

import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import java.util.ArrayList;
import java.util.List;     

public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;

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

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

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

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

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new OneFragment(), "ONE");
        adapter.addFragment(new TwoFragment(), "TWO");
        adapter.addFragment(new ThreeFragment(), "THREE");
        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
        }

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

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

        public void addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

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

来源：https://stackoverflow.com/questions/58725152/tabs-of-tab-layout-dont-display-anything