Android自带的TabLayout实现滑动翻页效果（实例）

Android自带的TabLayout在support包中，导包：

implementation 'com.android.support:support-v4:27.1.1'
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效果1

不带viewpager，tab只可点击，就是普通的控件。

TabLayout嵌套TabItem，可改造空间有限。tabLayout只能嵌套TabItem，其余会报错。

"@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#e1e1e1"
        app:tabSelectedTextColor="@color/colorAccent"
        app:tabTextColor="@color/black"
        app:tabIndicatorColor="@color/colorAccent"
        app:tabMode="fixed"
        app:tabIndicatorHeight="4dp">

        "@+id/tab1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/tab1"/>

        "@+id/tab2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/tab2"/>

        "@+id/tab3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/tab3"/>

    
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效果2

fragment + viewpager + tabLayout

虽然看着没多大区别，但里面是嵌套了3个Fragment，可以左右切换。

tabLayout.setupWithViewPager(viewPager) 执行这句之后，tabLayout布局嵌套的tabItem会失效，展示的每个tab是通过FragmentPagerAdapter的getPageTitle来获取的。等会儿可以源码解释下。

xml布局：就是简单的tabLayout和viewPager嵌套在一个垂直的linearLayout中

"1.0" encoding="utf-8"?>
"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"
    android:orientation="vertical"
    tools:context=".tablayout.TabLayoutActivity">

    "@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#e1e1e1"
        app:tabSelectedTextColor="@color/colorAccent"
        app:tabTextColor="@color/black"
        app:tabIndicatorColor="@color/colorAccent"
        app:tabMode="fixed"
        app:tabIndicatorHeight="4dp"/>

    "@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>


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kotlin代码

class TabLayoutActivity : AppCompatActivity() {

    var mFragmentList = arrayListOf()
    val mTabTitle = listOf("英语", "数学", "语文")
    var mAdapter: FragmentPagerAdapter? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_tab_layout)
        initTabLayout()
    }

    private fun initTabLayout() {
        mFragmentList.add(FragmentOne())
        mFragmentList.add(FragmentTwo())
        mFragmentList.add(FragmentThree()) 

        mAdapter = FragmentPagerAdapterNew(supportFragmentManager, mFragmentList, mTabTitle)
        viewPager.adapter = mAdapter //设置viewPager的adapter
        tabLayout.setupWithViewPager(viewPager) //建立tabLayout和ViewPager的联系
    }

    class FragmentPagerAdapterNew(val fragementManager: FragmentManager,
                                  val mFragmentList: List,
                                  val mTabTitle: List)
        : FragmentPagerAdapter(fragementManager) {
        override fun getItem(position: Int): Fragment {
            return mFragmentList[position] //切换tab展示的fragment
        }

        override fun getCount(): Int {
            return mFragmentList.size //总共有多少个tab/fragment
        }

        override fun getPageTitle(position: Int): CharSequence? {
            return mTabTitle[position] //展示tab的标题
        }
    }
}
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效果3

tab展示文字+图片的效果自行百度吧，因为我不打算用这个控件在项目中，用一个开源的更简单的FlycoTabLayout，下一篇就讲这个开源控件。

setViewPagerAdapter(viewPager)

现在解释下setViewPagerAdapter(viewPager)之后，tabLayout中的tabItem失效

首先removeAllTabs，然后根据mPagerAdapter.getCount得到tab个数，然后一个个通过addTab添加进行，newTab().setText(mPagerAdapter.getPageTitle(i)) tab设置的text就是我们刚刚说的， FragmentPagerAdapter里getPagerTitle()返回的啦

省略大部分代码

    public void setupWithViewPager(@Nullable ViewPager viewPager) {
        setupWithViewPager(viewPager, true);
    }

    public void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh) {
        setupWithViewPager(viewPager, autoRefresh, false);
    }

    private void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh,
            boolean implicitSetup) {
            final PagerAdapter adapter = viewPager.getAdapter();
            if (adapter != null) {
                setPagerAdapter(adapter, autoRefresh);
            }
    }
    
    void setPagerAdapter(@Nullable final PagerAdapter adapter, final boolean addObserver) {
        // Finally make sure we reflect the new adapter
        populateFromPagerAdapter();
    }
    
    void populateFromPagerAdapter() {
        removeAllTabs();  //就是这里啦，首先removeAllTabs

        if (mPagerAdapter != null) {
            final int adapterCount = mPagerAdapter.getCount();
            for (int i = 0; i < adapterCount; i++) {
                addTab(newTab().setText(mPagerAdapter.getPageTitle(i)), false);
            }

            // Make sure we reflect the currently set ViewPager item
            if (mViewPager != null && adapterCount > 0) {
                final int curItem = mViewPager.getCurrentItem();
                if (curItem != getSelectedTabPosition() && curItem < getTabCount()) {
                    selectTab(getTabAt(curItem));
                }
            }
        }
    }
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转载于:https://juejin.im/post/5b6409fc6fb9a04fb61506f8