java - ViewPager 中的选项卡未显示

Question

当我在我的设备上运行应用程序时，选项卡没有显示。没有错误，没有警告来分析和搜索问题的原因。但在添加 viewPager 之前，它是有效的。我已经完成了视频教程中显示的所有说明，从那里开始 https://www.youtube.com/watch?v=SHkdU9sznW8

这是我的代码:

MainActivity.java

package com.example.ganz.afex_with_default_navigation;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);

        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
        tabsPager tabsPager = new tabsPager(getSupportFragmentManager());

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


        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

和tabsPager.java:

package com.example.ganz.afex_with_default_navigation;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;

/**
 * Created by Ganz on 4/29/2018.
 */

public class tabsPager extends FragmentStatePagerAdapter {

    String [] titles = new String[] {"First", "Second"};

    public tabsPager(FragmentManager fm) {
        super(fm);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return titles[position];
    }

    @Override
    public Fragment getItem(int position) {

        switch (position) {

            case 0:
                BlankFragment blankFragment = new BlankFragment();
                return blankFragment;

            case 1:
                BlankFragment2 blankFragment2 = new BlankFragment2();
                return blankFragment2;

        }

        return null;
    }

    @Override
    public int getCount() {
        return 0;
    }
}

Answer 1

你的适配器不知道你有多少标签，改变这个:

@Override
    public int getCount() {
        return 0;
    }

到

@Override
    public int getCount() {
        return titles.length;
    }