Question

我有以下Viewpager2的代码，有两个主要问题：

片段内容涵盖了选项卡标题。如何调整它，以便内容从选项卡名称下面的行开始。
标签项未响应onTabSelectedListener，

activity_app.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".AppActivity">


    <com.google.android.material.tabs.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>

    <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"/>


</androidx.coordinatorlayout.widget.CoordinatorLayout>

AppActivity

import android.net.Uri
import android.os.Bundle
import com.google.android.material.tabs.TabLayout
import androidx.appcompat.app.AppCompatActivity
import com.google.android.material.tabs.TabLayoutMediator
import kotlinx.android.synthetic.main.activity_app.*

class AppActivity : AppCompatActivity(), BlankFragment.OnFragmentInteractionListener {
    override fun onFragmentInteraction(uri: Uri) {
       // TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }
    // private val arrayList = arrayListOf()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_app)

        viewpager.adapter = AppViewPagerAdapter(supportFragmentManager, lifecycle)

        TabLayoutMediator(tabs, viewpager, object : TabLayoutMediator.OnConfigureTabCallback {
            override fun onConfigureTab(tab: TabLayout.Tab, position: Int) {
                // Styling each tab here
                tab.text = "Tab $position"
            }
        }).attach()
    }
}

AppViewPagerAdapter

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.lifecycle.Lifecycle
import androidx.viewpager2.adapter.FragmentStateAdapter


class AppViewPagerAdapter(fragmentManager: FragmentManager, lifecycle: Lifecycle) :
    FragmentStateAdapter(fragmentManager, lifecycle) {
    override fun getItem(position: Int): Fragment {

        return when (position) {
            0 -> BlankFragment()
            1 -> BlankFragment()
            else -> BlankFragment()
        }
    }

    override fun getItemCount(): Int {
        return 3
    }
}

fragment_blank.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:tools="http://schemas.android.com/tools"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             tools:context=".BlankFragment">

    <!-- TODO: Update blank fragment layout -->


    <Button
            android:text="Button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" android:id="@+id/button"/>
</FrameLayout>

TabLayoutMediator

package com.google.android.material.tabs

import androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_DRAGGING
import androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_IDLE
import androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_SETTLING
import androidx.recyclerview.widget.RecyclerView
import androidx.viewpager2.widget.ViewPager2
import java.lang.ref.WeakReference

/**
 * A mediator to link a TabLayout with a ViewPager2. The mediator will synchronize the ViewPager2's
 * position with the selected tab when a tab is selected, and the TabLayout's scroll position when
 * the user drags the ViewPager2.
 *
 *
 * Establish the link by creating an instance of this class, make sure the ViewPager2 has an
 * adapter and then call [.attach] on it. When creating an instance of this class, you must
 * supply an implementation of [OnConfigureTabCallback] in which you set the text of the tab,
 * and/or perform any styling of the tabs that you require.
 */
class TabLayoutMediator(
    private val tabLayout: TabLayout,
    private val viewPager: ViewPager2,
    private val autoRefresh: Boolean,
    private val onConfigureTabCallback: OnConfigureTabCallback
) {
    private var adapter: RecyclerView.Adapter<*>? = null
    private var attached: Boolean = false

    private var onPageChangeCallback: TabLayoutOnPageChangeCallback? = null
    private var onTabSelectedListener: TabLayout.OnTabSelectedListener? = null
    private var pagerAdapterObserver: RecyclerView.AdapterDataObserver? = null

    /**
     * A callback interface that must be implemented to set the text and styling of newly created
     * tabs.
     */
    interface OnConfigureTabCallback {
        /**
         * Called to configure the tab for the page at the specified position. Typically calls [ ][TabLayout.Tab.setText], but any form of styling can be applied.
         *
         * @param tab The Tab which should be configured to represent the title of the item at the given
         * position in the data set.
         * @param position The position of the item within the adapter's data set.
         */
        fun onConfigureTab(tab: TabLayout.Tab, position: Int)
    }

    constructor(
        tabLayout: TabLayout,
        viewPager: ViewPager2,
        onConfigureTabCallback: OnConfigureTabCallback
    ) : this(tabLayout, viewPager, true, onConfigureTabCallback) {
    }

    /**
     * Link the TabLayout and the ViewPager2 together.
     *
     * @throws IllegalStateException If the mediator is already attached, or the ViewPager2 has no
     * adapter.
     */
    fun attach() {
        if (attached) {
            throw IllegalStateException("TabLayoutMediator is already attached")
        }
        adapter = viewPager.adapter
        if (adapter == null) {
            throw IllegalStateException(
                "TabLayoutMediator attached before ViewPager2 has an " + "adapter"
            )
        }
        attached = true

        // Add our custom OnPageChangeCallback to the ViewPager
        onPageChangeCallback = TabLayoutOnPageChangeCallback(tabLayout)
        viewPager.registerOnPageChangeCallback(onPageChangeCallback!!)

        // Now we'll add a tab selected listener to set ViewPager's current item
        onTabSelectedListener = ViewPagerOnTabSelectedListener(viewPager)
        tabLayout.addOnTabSelectedListener(onTabSelectedListener!!)

        // Now we'll populate ourselves from the pager adapter, adding an observer if
        // autoRefresh is enabled
        if (autoRefresh) {
            // Register our observer on the new adapter
            pagerAdapterObserver = PagerAdapterObserver()
            adapter!!.registerAdapterDataObserver(pagerAdapterObserver!!)
        }

        populateTabsFromPagerAdapter()

        // Now update the scroll position to match the ViewPager's current item
        tabLayout.setScrollPosition(viewPager.currentItem, 0f, true)
    }

    /** Unlink the TabLayout and the ViewPager  */
    fun detach() {
        adapter!!.unregisterAdapterDataObserver(pagerAdapterObserver!!)
        tabLayout.removeOnTabSelectedListener(onTabSelectedListener!!)
        viewPager.unregisterOnPageChangeCallback(onPageChangeCallback!!)
        pagerAdapterObserver = null
        onTabSelectedListener = null
        onPageChangeCallback = null
        attached = false
    }

    internal fun populateTabsFromPagerAdapter() {
        tabLayout.removeAllTabs()

        if (adapter != null) {
            val adapterCount = adapter!!.itemCount
            for (i in 0 until adapterCount) {
                val tab = tabLayout.newTab()
                onConfigureTabCallback.onConfigureTab(tab, i)
                tabLayout.addTab(tab, false)
            }

            // Make sure we reflect the currently set ViewPager item
            if (adapterCount > 0) {
                val currItem = viewPager.currentItem
                if (currItem != tabLayout.selectedTabPosition) {
                    tabLayout.getTabAt(currItem)!!.select()
                }
            }
        }
    }

    /**
     * A [ViewPager2.OnPageChangeCallback] class which contains the necessary calls back to the
     * provided [TabLayout] so that the tab position is kept in sync.
     *
     *
     * This class stores the provided TabLayout weakly, meaning that you can use [ ][ViewPager2.registerOnPageChangeCallback] without removing the
     * callback and not cause a leak.
     */
    private class TabLayoutOnPageChangeCallback internal constructor(tabLayout: TabLayout) :
        ViewPager2.OnPageChangeCallback() {
        private val tabLayoutRef: WeakReference<TabLayout> = WeakReference(tabLayout)
        private var previousScrollState: Int = 0
        private var scrollState: Int = 0

        init {
            reset()
        }

        override fun onPageScrollStateChanged(state: Int) {
            previousScrollState = scrollState
            scrollState = state
        }

        override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {
            val tabLayout = tabLayoutRef.get()
            if (tabLayout != null) {
                // Only update the text selection if we're not settling, or we are settling after
                // being dragged
                val updateText = scrollState != SCROLL_STATE_SETTLING || previousScrollState == SCROLL_STATE_DRAGGING
                // Update the indicator if we're not settling after being idle. This is caused
                // from a setCurrentItem() call and will be handled by an animation from
                // onPageSelected() instead.
                val updateIndicator =
                    !(scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE)
                tabLayout.setScrollPosition(position, positionOffset, updateText, updateIndicator)
            }
        }

        override fun onPageSelected(position: Int) {
            val tabLayout = tabLayoutRef.get()
            if (tabLayout != null
                && tabLayout.selectedTabPosition != position
                && position < tabLayout.tabCount
            ) {
                // Select the tab, only updating the indicator if we're not being dragged/settled
                // (since onPageScrolled will handle that).
                val updateIndicator =
                    scrollState == SCROLL_STATE_IDLE || scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE
                tabLayout.selectTab(tabLayout.getTabAt(position), updateIndicator)
            }
        }

        internal fun reset() {
            scrollState = SCROLL_STATE_IDLE
            previousScrollState = scrollState
        }
    }

    /**
     * A [TabLayout.OnTabSelectedListener] class which contains the necessary calls back to the
     * provided [ViewPager2] so that the tab position is kept in sync.
     */
    private class ViewPagerOnTabSelectedListener internal constructor(private val viewPager: ViewPager2) :
        TabLayout.OnTabSelectedListener {

        override fun onTabSelected(tab: TabLayout.Tab) {
            viewPager.setCurrentItem(tab.position, true)
        }

        override fun onTabUnselected(tab: TabLayout.Tab) {
            // No-op
        }

        override fun onTabReselected(tab: TabLayout.Tab) {
            // No-op
        }
    }

    private inner class PagerAdapterObserver internal constructor() : RecyclerView.AdapterDataObserver() {

        override fun onChanged() {
            populateTabsFromPagerAdapter()
        }

        override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
            populateTabsFromPagerAdapter()
        }

        override fun onItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?) {
            populateTabsFromPagerAdapter()
        }

        override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
            populateTabsFromPagerAdapter()
        }

        override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
            populateTabsFromPagerAdapter()
        }

        override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
            populateTabsFromPagerAdapter()
        }
    }
}

结果的屏幕截图

Answer 1

这是完整的代码 TabLayout-with-viewpager2-

ViewPager2

没有问题

问题出在您的布局文件上

当我用 CoordinatorLayout

更改您的 LinearLayout 时，检查结果

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout
        android:orientation="vertical"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <com.google.android.material.tabs.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>

    <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>


</LinearLayout>

输出

遵循这些步骤

更新您的dependencies

implementation 'com.google.android.material:material:1.1.0-alpha08'
implementation 'androidx.viewpager2:viewpager2:1.0.0-beta02'

无需为TabLayoutMediator创建自定义类，该类将包含在implementation 'com.google.android.material:material:1.1.0-alpha08'
中

示例代码

R.layout.activity_main

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <com.google.android.material.appbar.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <androidx.appcompat.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"/>

        <com.google.android.material.tabs.TabLayout
                android:id="@+id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"/>
    </com.google.android.material.appbar.AppBarLayout>

    <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/viewpager"
            app:layout_anchor="@id/tabs"
            app:layout_anchorGravity="bottom"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
    />


</androidx.coordinatorlayout.widget.CoordinatorLayout>

MainActivity

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
import com.google.android.material.tabs.TabLayoutMediator

import com.google.android.material.tabs.TabLayout


class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

//        setSupportActionBar(toolbar)
        viewpager.adapter = AppViewPagerAdapter(supportFragmentManager, lifecycle)

        TabLayoutMediator(tabs, viewpager, object : TabLayoutMediator.OnConfigureTabCallback {
            override fun onConfigureTab(tab: TabLayout.Tab, position: Int) {
                // Styling each tab here
                tab.text = "Tab $position"
            }
        }).attach()


    }
}

输出

Answer 2

尝试一下，在if else中添加TabLayoutMediator.onConfigureTab语句，它对我有用。我不为Kotlin编写代码。

TabLayoutMediator(tabs, viewpager, object : TabLayoutMediator.OnConfigureTabCallback {
        override fun onConfigureTab(tab: TabLayout.Tab, position: Int) {
            // if (position == 0){tab.setText("First Tab");}
            tab.text = "Tab $position"
        }
    }).attach()

Answer 3

在我的情况下，使用tablayout的viewpager和viewpager2正常工作，但数据未刷新。

我在Viewpager2中通过添加adapter.notifyItemChanged(position);来解决此问题，如下所示：

viewPager = (ViewPager2) android.findViewById(R.id.view_pager);
    tabLayout = (TabLayout) android.findViewById(R.id.tab_layout);


    ViewPagerAdapter adapter = new ViewPagerAdapter(getFragmentManager(),getLifecycle());
    viewPager.setAdapter(adapter);

    viewPager.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            super.onPageScrolled(position, positionOffset, positionOffsetPixels);
        }

        @Override
        public void onPageSelected(int position){
            super.onPageSelected(position);
            adapter.notifyItemChanged(position);
        }
    });

每次单击选项卡时，以上代码都会刷新代码。但滑动Viewpager时不会。

ViewPager2片段与选项卡式项目重叠

3 个答案: