设置选项卡图标时出现空指针异常

Question

我正在尝试在选项卡中设置图标，但我不断收到空指针异常。我无法理解为什么会发生这种情况？

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(TAG, "onCreate: starting");
    setupNavigationView();
    setupViewPager();

}

//Responsible for adding the 3 tabs:camera,main,message
private void setupViewPager(){
    SectionPagerAdapter sectionPagerAdapter = new SectionPagerAdapter(getSupportFragmentManager());
    sectionPagerAdapter.addFragment(new CameraFragment());
    sectionPagerAdapter.addFragment(new MainFragment());
    sectionPagerAdapter.addFragment(new MessagesFragment());
    ViewPager viewPager = findViewById(R.id.container);
    viewPager.setAdapter(sectionPagerAdapter);

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

    layout.getTabAt(0).setIcon(R.drawable.ic_camera);
    layout.getTabAt(1).setIcon(R.drawable.ic_instagram);
    layout.getTabAt(2).setIcon(R.drawable.ic_action_name);


}

错误：

  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
                                                                                Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.design.widget.TabLayout$Tab android.support.design.widget.TabLayout$Tab.setIcon(int)' on a null object reference
                                                                                   at android.vishal.instagramclone.MainActivity.MainActivity.setupViewPager(MainActivity.java:47)
                                                                                   at android.vishal.instagramclone.MainActivity.MainActivity.onCreate(MainActivity.java:31)

Answer 1

您遇到此问题是因为您尚未添加选项卡并尝试设置图标

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//Add tabs icon with setIcon() or simple text with .setText()\n tabLayout.addTab(tabLayout.newTab().setIcon(R.mipmap.ic_home));\n\xc2\xa0tabLayout.addTab(tabLayout.newTab().setIcon(R.mipmap.ic_profile));\n tabLayout.addTab(tabLayout.newTab().setIcon(R.mipmap.ic_settings));\n

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欲了解更多详情，请查看下面的链接

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https://gist.github.com/faizsiddiqui/9af9cea9051335e1ad3f

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