android-studio - 向Android Developer Studio的选项卡式事件模板添加片段

Question

初学者在这里。使用Android Developer Studios标签式 Activity 模板创建应用。我有两个xml，即模板要包含的生成的fragment_main.xml和要成为第二个选项卡的secondtab.xml。

这是模板生成的代码:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val sectionsPagerAdapter = SectionsPagerAdapter(this, supportFragmentManager)
    val viewPager: ViewPager = findViewById(R.id.view_pager)
    viewPager.adapter = sectionsPagerAdapter
    val tabs: TabLayout = findViewById(R.id.tabs)
    tabs.setupWithViewPager(viewPager)
    val fab: FloatingActionButton = findViewById(R.id.fab)

    fab.setOnClickListener { view ->
        Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show()
    }

我一直在阅读ViewPager文档，而我发现很多都是从头开始做的，而且我很难理解。我觉得我缺少明显的东西。如何将我的secondtab.xml添加到此预生成的模板中，以便在用户单击第二个选项卡时显示它？

Answer 1

您的SectionsPagerAdapter getItem函数应如下所示:

class SectionsPagerAdapter(
    private val context: Context,
    fm: FragmentManager
) : FragmentPagerAdapter(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {

    override fun getItem(position: Int) = when (position) {
        0 -> FirstTabFragment()
        1 -> SecondTabFragment()
        else -> error("Unknown")
    }

    override fun getPageTitle(position: Int) = context.resources.getString(TAB_TITLES[position])

    override fun getCount() = 2
}

因为默认情况下，此模板中的 SectionsPagerAdapter始终创建PlaceholderFragment:

 override fun getItem(position: Int): Fragment {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        return PlaceholderFragment.newInstance(position + 1)
 } 

但是在您的情况下，您需要使用两个不同的片段以及两个不同的xml布局，如下所示:

class FirstTabFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val root = inflater.inflate(R.layout.fragment_main, container, false)
        val textView: TextView = root.findViewById(R.id.section_label)
        return root
    }
}

class SecondTabFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val root = inflater.inflate(R.layout.secondtab, container, false)
        val textView: TextView = root.findViewById(R.id.section_label)
        return root
    }
}

还请确保添加:

<TextView
android:id="@+id/section_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="@dimen/activity_horizontal_margin"
android:layout_marginTop="@dimen/activity_vertical_margin"
android:layout_marginEnd="@dimen/activity_horizontal_margin"
android:layout_marginBottom="@dimen/activity_vertical_margin"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="@+id/constraintLayout"
tools:layout_constraintLeft_creator="1"
tools:layout_constraintTop_creator="1" />

到片段xml