今天我所要作的笔记是：

可切换式的卡片CardView。

Java代码部分

1、我们要根据自己的当前版本号添加相对应的一个依赖：

implementation 'com.android.support:cardview-v7:28.0.0'

2、编写Fragment，在自己需要Activity中添加Fragment，在该Fragment编写如下代码。我的Fragment是DiscoveryFragment。

public class DiscoveryFragment extends Fragment {

    private ViewPager mViewPager;

    private CardPagerAdapter mCardAdapter;
    private ShadowTransformer mCardShadowTransformer;
    private CardView mCardView;
    public DiscoveryFragment() {
        // Required empty public constructor
    }

    View view;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        if(view == null) {
            view = inflater.inflate(R.layout.fragment_discovery, container, false);
            mCardView = view.findViewById(R.id.cardView);
            mCardView.setMaxCardElevation(mCardView.getCardElevation()
                    * CardAdapter.MAX_ELEVATION_FACTOR);
            initCard();
        }
        return view;
    }

    private void initCard() {
        mViewPager = view.findViewById(R.id.viewPager);

        mCardAdapter = new CardPagerAdapter();
        mCardAdapter.addCardItem(new CardItem(R.string.title_1, R.string.text_1));
        mCardAdapter.addCardItem(new CardItem(R.string.title_2, R.string.text_1));
        mCardAdapter.addCardItem(new CardItem(R.string.title_3, R.string.text_1));
        mCardAdapter.addCardItem(new CardItem(R.string.title_4, R.string.text_1));

        mCardShadowTransformer = new ShadowTransformer(mViewPager, mCardAdapter);
        mCardShadowTransformer.enableScaling(true);

        mViewPager.setAdapter(mCardAdapter);
        mViewPager.setPageTransformer(false, mCardShadowTransformer);
        mViewPager.setOffscreenPageLimit(3);
    }
    public CardView getCardView() {
        return mCardView;
    }
}

3、CardFragmentPagerAdapter

public class CardFragmentPagerAdapter extends FragmentStatePagerAdapter implements CardAdapter {

    private List<DiscoveryFragment> mFragments;
    private float mBaseElevation;

    public CardFragmentPagerAdapter(FragmentManager fm, float baseElevation) {
        super(fm);
        mFragments = new ArrayList<>();
        mBaseElevation = baseElevation;

        for(int i = 0; i< 5; i++){
            addCardFragment(new DiscoveryFragment());
        }
    }

    @Override
    public float getBaseElevation() {
        return mBaseElevation;
    }

    @Override
    public CardView getCardViewAt(int position) {
        return mFragments.get(position).getCardView();
    }

    @Override
    public int getCount() {
        return mFragments.size();
    }

    @Override
    public Fragment getItem(int position) {
        return mFragments.get(position);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Object fragment = super.instantiateItem(container, position);
        mFragments.set(position, (DiscoveryFragment) fragment);
        return fragment;
    }

    public void addCardFragment(DiscoveryFragment fragment) {
        mFragments.add(fragment);
    }

}

4、CardPagerAdapter

public class CardPagerAdapter extends PagerAdapter implements CardAdapter {

    private List<CardView> mViews;
    private List<CardItem> mData;
    private float mBaseElevation;

    public CardPagerAdapter() {
        mData = new ArrayList<>();
        mViews = new ArrayList<>();
    }

    public void addCardItem(CardItem item) {
        mViews.add(null);
        mData.add(item);
    }

    public float getBaseElevation() {
        return mBaseElevation;
    }

    @Override
    public CardView getCardViewAt(int position) {
        return mViews.get(position);
    }

    @Override
    public int getCount() {
        return mData.size();
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        View view = LayoutInflater.from(container.getContext())
                .inflate(R.layout.adapter, container, false);
        container.addView(view);
        bind(mData.get(position), view);
        CardView cardView =  view.findViewById(R.id.cardView);

        if (mBaseElevation == 0) {
            mBaseElevation = cardView.getCardElevation();
        }

        cardView.setMaxCardElevation(mBaseElevation * MAX_ELEVATION_FACTOR);
        mViews.set(position, cardView);
        return view;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((View) object);
        mViews.set(position, null);
    }

    private void bind(CardItem item, View view) {
        TextView titleTextView = (TextView) view.findViewById(R.id.titleTextView);
        TextView contentTextView = (TextView) view.findViewById(R.id.contentTextView);
        titleTextView.setText(item.getTitle());
        contentTextView.setText(item.getText());
    }

}

5、CardItem

public class CardItem {

    private int mTextResource;
    private int mTitleResource;

    public CardItem(int title, int text) {
        mTitleResource = title;
        mTextResource = text;
    }

    public int getText() {
        return mTextResource;
    }

    public int getTitle() {
        return mTitleResource;
    }
}

6、ShadowTransformer

public class ShadowTransformer implements ViewPager.OnPageChangeListener, ViewPager.PageTransformer {

    private ViewPager mViewPager;
    private CardAdapter mAdapter;
    private float mLastOffset;
    private boolean mScalingEnabled;

    public ShadowTransformer(ViewPager viewPager, CardAdapter adapter) {
        mViewPager = viewPager;
        viewPager.addOnPageChangeListener(this);
        mAdapter = adapter;
    }

    public void enableScaling(boolean enable) {
        if (mScalingEnabled && !enable) {
            // shrink main card
            CardView currentCard = mAdapter.getCardViewAt(mViewPager.getCurrentItem());
            if (currentCard != null) {
                currentCard.animate().scaleY(1);
                currentCard.animate().scaleX(1);
            }
        }else if(!mScalingEnabled && enable){
            // grow main card
            CardView currentCard = mAdapter.getCardViewAt(mViewPager.getCurrentItem());
            if (currentCard != null) {
                currentCard.animate().scaleY(1.1f);
                currentCard.animate().scaleX(1.1f);
            }
        }

        mScalingEnabled = enable;
    }

    @Override
    public void transformPage(View page, float position) {

    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        int realCurrentPosition;
        int nextPosition;
        float baseElevation = mAdapter.getBaseElevation();
        float realOffset;
        boolean goingLeft = mLastOffset > positionOffset;

        // If we're going backwards, onPageScrolled receives the last position
        // instead of the current one
        if (goingLeft) {
            realCurrentPosition = position + 1;
            nextPosition = position;
            realOffset = 1 - positionOffset;
        } else {
            nextPosition = position + 1;
            realCurrentPosition = position;
            realOffset = positionOffset;
        }

        // Avoid crash on overscroll
        if (nextPosition > mAdapter.getCount() - 1
                || realCurrentPosition > mAdapter.getCount() - 1) {
            return;
        }

        CardView currentCard = mAdapter.getCardViewAt(realCurrentPosition);

        // This might be null if a fragment is being used
        // and the views weren't created yet
        if (currentCard != null) {
            if (mScalingEnabled) {
                currentCard.setScaleX((float) (1 + 0.1 * (1 - realOffset)));
                currentCard.setScaleY((float) (1 + 0.1 * (1 - realOffset)));
            }
            currentCard.setCardElevation((baseElevation + baseElevation
                    * (CardAdapter.MAX_ELEVATION_FACTOR - 1) * (1 - realOffset)));
        }

        CardView nextCard = mAdapter.getCardViewAt(nextPosition);

        // We might be scrolling fast enough so that the next (or previous) card
        // was already destroyed or a fragment might not have been created yet
        if (nextCard != null) {
            if (mScalingEnabled) {
                nextCard.setScaleX((float) (1 + 0.1 * (realOffset)));
                nextCard.setScaleY((float) (1 + 0.1 * (realOffset)));
            }
            nextCard.setCardElevation((baseElevation + baseElevation
                    * (CardAdapter.MAX_ELEVATION_FACTOR - 1) * (realOffset)));
        }

        mLastOffset = positionOffset;
    }

    @Override
    public void onPageSelected(int position) {

    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
}

7、CardAdapter

public interface CardAdapter {

    int MAX_ELEVATION_FACTOR = 8;

    float getBaseElevation();

    CardView getCardViewAt(int position);

    int getCount();
}

XML文件

1、CardPagerAdapter的布局文件adapter

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/cardView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    app:cardUseCompatPadding="true">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:padding="24dp">

            <TextView
                android:id="@+id/titleTextView"
                style="@style/TextAppearance.AppCompat.Title"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" />

            <TextView
                android:id="@+id/contentTextView"
                style="@style/TextAppearance.AppCompat.Body1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="24dp"/>

            <Button
                style="@style/ButtonStyle"
                android:layout_width="match_parent"
                android:layout_height="@dimen/dp40"
                android:layout_marginTop="@dimen/dp100"
                android:layout_gravity="bottom"
                android:background="@color/green_theme"
                android:text="开始悦读" />
        </LinearLayout>

    </FrameLayout>

</android.support.v7.widget.CardView>

2、fragment_discovery

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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"
    android:orientation="vertical"
    android:background="@color/greyf3"
    tools:context=".main_code.about_fragment.about_discovery.DiscoveryFragment">
    <android.support.v7.widget.CardView
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/cardView"
        app:cardUseCompatPadding="true"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center">

        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="@dimen/dp400"
            android:layout_gravity="center"
            android:clipToPadding="false"
            android:overScrollMode="never"
            android:paddingLeft="@dimen/dp40"
            android:paddingRight="@dimen/dp40"
            android:paddingStart="@dimen/dp60" />
    </android.support.v7.widget.CardView>

</LinearLayout>

以上。
代码来自：（致谢）
https://blog.csdn.net/chenzheng8975/article/details/76976122