将图标设置为选项卡布局时应用程序崩溃

Question

我正在 android 中创建一个带有导航视图的 tabLayout。我想为选项卡布局的选项卡设置图标。当我使用 setIcon 函数时，应用程序抛出空指针异常并崩溃。请帮我。

public class navHomeActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

private TabLayout tabLayout;
private ViewPager viewPager;
int icons[] = {
        R.drawable.icon1,
        R.drawable.icon2,
        R.drawable.icon3};

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

    viewPager = (ViewPager) findViewById(R.id.homeViewPager);
    setupViewPager(viewPager);
    setupTabIcons();

    tabLayout = (TabLayout) findViewById(R.id.tabHomeLayout);
    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.setDrawerListener(toggle);
    toggle.syncState();

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


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

private void setupViewPager(ViewPager viewPager) {
    ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
    adapter.addFrag(new OneFragment(), "tab1");
    adapter.addFrag(new OneFragment(), "tab2");
    adapter.addFrag(new OneFragment(), "tab3");
    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);
    }

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

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

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

    }

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


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

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    Fragment fragment = null;

    int id = item.getItemId();

    if (id == R.id.nav_home)
        {
            setTitle("Home");
        }
    else if (id == R.id.frag2)
        {

        }
    else if (id == R.id.frag3)
        {

        }
    else if (id == R.id.frag4)
        {

        }
    else if (id == R.id.frag5)
        {

        }
    else if (id == R.id.frag6)
        {

        }
    else if (id == R.id.frag7)
        {

        }
    else if (id == R.id.frag8)
        {

        }

    try {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.homeContentLayout, fragment).commit();
    }catch (NullPointerException e){
        Log.d("Exception", e.toString());}


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

LogCat:

致命异常：主要 java.lang.RuntimeException：无法启动活动 ComponentInfo{com.techsponential.cricbash/com.techsponential.cricbash.navHomeActivity}：java.lang.NullPointerException：尝试调用虚拟方法 'android.support.design.widget .TabLayout$Tab android.support.design.widget.TabLayout.getTabAt(int)' 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.爪哇：2490) 在 android.app.ActivityThread.-wrap11(ActivityThread.java) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 在 android.os.Handler.dispatchMessage(Handler.java:102) 在 android .os.Looper.loop(Looper.java:148) 在 android.app.ActivityThread.main(ActivityThread.java:5443) 在 java.lang.reflect.Method。invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 由：java. lang.NullPointerException：尝试在 com.techsponential.cricbash.navHomeActivity 的空对象引用上调用虚拟方法“android.support.design.widget.TabLayout$Tab android.support.design.widget.TabLayout.getTabAt(int)”。 setupTabIcons(navHomeActivity.java:57) 在 com.techsponential.cricbash.navHomeActivity.onCreate(navHomeActivity.java:40) 在 android.app.Activity.performCreate(Activity.java:6245) 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)navHomeActivity.onCreate(navHomeActivity.java:40) at android.app.Activity.performCreate(Activity.java:6245) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) at android.app.ActivityThread.performLaunchActivity(ActivityThread) .java:2379) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)navHomeActivity.onCreate(navHomeActivity.java:40) at android.app.Activity.performCreate(Activity.java:6245) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) at android.app.ActivityThread.performLaunchActivity(ActivityThread) .java:2379) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)java:6245) 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)java:6245) 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)[2379] 第2379话[2379] 第2379话

在 android.app.ActivityThread.-wrap11(ActivityThread.java) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 在 android.os.Handler.dispatchMessage(Handler.java:102) 在 android.os .Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5443) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit $MethodAndArgsCaller.run(ZygoteInit.java:728)

在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

Answer 1

您在调用setupTabIcons()之前调用findViewById()以检索TabLayout或添加任何选项卡。尝试改变：

setupTabIcons();

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

到：

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