通过数据绑定库在 MVVM 架构中使用 Tab 布局

Question

我正在开发一个具有选项卡布局的应用程序作为图像。

我想使用带有数据绑定库的 MVVM 架构，但我是这个框架的新手。

我可以在不使用 MVVM 的情况下执行此操作，方法是使用 ViewPager 作为此示例正常设置选项卡布局。

没有 MVVM 和数据绑定的正常选项卡布局：

activity_main.xml:

    <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.v7.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" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMode="fixed"
            app:tabGravity="fill"/>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"  />
</android.support.design.widget.CoordinatorLayout>

MainActivity.java:

    public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

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

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new OneFragment(), "ONE");
        adapter.addFragment(new TwoFragment(), "TWO");
        adapter.addFragment(new ThreeFragment(), "THREE");
        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 addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

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

MVVM 中的选项卡布局：

将 MVVM 与数据绑定库一起使用时，我们将不得不为选项卡布局视图使用视图模型。

而且我不知道如何在 XML 和视图模型中设置选项卡布局。如何使用数据绑定库处理诸如“点击布局的一个选项卡”之类的事件

有数据绑定库在 MVVM 中使用 Tab 布局的示例吗？

感谢您的帮助。

Answer 1

主要活动-

    public class MainActivity extends Activity 
    {
        @Override
        protected void onCreate(@Nullable final Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            App.get(this).component().inject(this);
            ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            binding.setHandler(this);
            binding.setManager(getSupportFragmentManager());
        }
        
        @BindingAdapter({"bind:handler"})
        public static void bindViewPagerAdapter(final ViewPager view, final MainActivity activity)
        {
            final MainActionsAdapter adapter = new MainActionsAdapter(view.getContext(), activity.getSupportFragmentManager());
            view.setAdapter(adapter);
        }
        
        @BindingAdapter({"bind:pager"})
        public static void bindViewPagerTabs(final TabLayout view, final ViewPager pagerView)
        {
            view.setupWithViewPager(pagerView, true);
        }
    
    }

xml -

    <layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:fresco="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">
    
        <data>
    
            <import type="android.view.View" />
    
            <variable
                name="handler"
                type="com.ui.main.MainActivity" />
    
            <variable
                name="manager"
                type="android.support.v4.app.FragmentManager" />
        </data>
    
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
    
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:animateLayoutChanges="true"
                app:title="@string/app_name"
                app:titleMarginStart="8dp" />
    
            <android.support.design.widget.TabLayout
                android:id="@+id/tab_layout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:pager="@{(pager)}">
            </android.support.design.widget.TabLayout>
    
            <android.support.v4.view.ViewPager
                android:id="@+id/pager"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:handler="@{handler}" />
    
        </LinearLayout>
    
    </layout>

适配器 -

    public class MainSectionsAdapter extends FragmentPagerAdapter
    {
        private static final int CONTACTS = 0;
        private static final int CALLS = 1;
        private static final int CHATS = 2;
        
        private static final int[] TABS = new int[]{CONTACTS, CALLS, CHATS};
        
        private Context mContext;
        
        public MainSectionsAdapter(final Context context, final FragmentManager fm)
        {
            super(fm);
            mContext = context.getApplicationContext();
        }
        
        @Override
        public Fragment getItem(int position)
        {
            switch (TABS[position])
            {
                case CONTACTS:
                    return ContactsFragment.newInstance();
                case CALLS:
                    return CallsFragment.newInstance();
                case CHATS:
                    return ChatsFragment.newInstance();
            }
            return null;
        }
        
        @Override
        public int getCount()
        {
            return TABS.length;
        }
        
        @Override
        public CharSequence getPageTitle(int position)
        {
            switch (TABS[position])
            {
                case CONTACTS:
                    return mContext.getResources().getString(R.string.contacts);
                case CALLS:
                    return mContext.getResources().getString(R.string.calls);
                case CHATS:
                    return mContext.getResources().getString(R.string.chats);
            }
            return null;
        }
    }

Answer 2

这是我使用 databinding 对 setUpWithViewpager 的解决方案：

    public class BindingUtil
    {
        @BindingAdapter({ "setUpWithViewpager" })
        public static void setUpWithViewpager(final TabLayout tabLayout, ViewPager viewPager)
        {
            viewPager.addOnAdapterChangeListener(new ViewPager.OnAdapterChangeListener()
            {
                @Override
                public void onAdapterChanged(@NonNull ViewPager viewPager, @Nullable PagerAdapter oldAdapter, @Nullable PagerAdapter newAdapter)
                {
                    if (oldAdapter == null && (newAdapter == null || newAdapter.getCount() == 0))
                    {
                        // this function will helpful when 
                        // we don't create viewpager immediately 
                        // when view created (this mean we create
                        // will pager after a period time)
                        return;
                    }
                    tabLayout.setupWithViewPager(viewPager);
                }
            });
        }
    }

xml

<android.support.design.widget.TabLayout
     ... 
     app:setUpWithViewpager="@{ viewPager }"
/>

<android.support.v4.view.ViewPager
     ...
     android:id="@+id/viewPager"
     app:adapter="@{viewModel.pagerAdapter}"
/>

ViewModel

    public class MainViewModel extends BaseObservable
    {
        
        @Bindable
        public PagerAdapter getPagerAdapter()
        {
            return adapter;
        }
    
        private void createViewPagerAdapter()
        {
            ...
            notifyPropertyChanged(BR.pagerAdapter);
        }
    }

full demo project here

Answer 3

我不确定这是否是最近新引入的，但是 Android 支持版本 27.1.1，您甚至不需要自定义数据绑定适配器，您可以简单地使用：

<android.support.design.widget.TabLayout
                android:id="@+id/tl_1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:setupWithViewPager="@{some_fragment_viewpager}"
                app:tabSelectedTextColor="@android:color/white"
                app:tabTextColor="@color/v5_grey_55"
                />


        <android.support.v4.view.ViewPager
            android:id="@+id/some_fragment_viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:addOnPageChangeListener="@{vm.pageChangeListener}"
            app:setAdapter="@{vm.pageAdapter}"
            app:setCurrentItem="@{vm.pageChangeListener.currentPosition}"
            />

注意 app:setupWithViewPager="@{some_fragment_viewpager}" 中的 viewPager 变量指向 android:id="@+id/some_fragment_viewpager"。这就是对 ViewPager 的引用的完成方式（就像我知道的魔术一样）！

视图模型

public class SomeViewModel {
  public ViewPager.OnPageChangeListener pageChangeListener;
  public SomeFragmentPagerAdapter pagerAdapter;
  // ...
}

FragmentPagerAdapter

public classs SomeFragmentPagerAdapter extends FragmentPagerAdapter {
  public Boolean currentPosition;
}

Answer 4

如所示，它对我有用，但当我们在括号中提供 viewPager 的 ID 作为对 tabLayout 的引用时它显示绑定错误。

我通过简单地提供不带括号的 ID 并提供 ViewPager 的驼峰式 ID 解决了这个问题。

通过数据绑定库在 MVVM 架构中使用 Tab 布局

Use Tab layout in MVVM architecture with the data binding library

android

mvvm

data-binding

android-tablayout

android-databinding