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 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 mViews;

private List 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

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">

android:layout_width="match_parent"

android:layout_height="wrap_content">

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:orientation="vertical"

android:padding="24dp">

android:id="@+id/titleTextView"

style="@style/TextAppearance.AppCompat.Title"

android:layout_width="wrap_content"

android:layout_height="wrap_content" />

android:id="@+id/contentTextView"

style="@style/TextAppearance.AppCompat.Body1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="24dp"/>

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" />

2、fragment_discovery

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">

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: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" />