Android 进阶之重要的控件 CardView

Android working with Card View and Recycler View

翻译：林晓海
文章地址：http://www.androidhive.info/2016/05/android-working-with-card-view-and-recycler-view/

CardView 是 Material Design 引入的又一个重要的新控件，使用CardView可以用一个带有阴影和圆弧的卡片来展示信息，CardView继承自FragmentLayout，可以通过兼容包的形式向后兼容到Androd 2.x版本。

可以将CardView和RecycleView结合实现漂亮的UI效果，通过这篇文章我们可以通过创建一个漂亮的Music app 来学习如何结合CardView和RecycleView。

怎样添加CardView？
为了在你的app中使用CardView，添加CardView依赖到build.gradle，然后同步下项目：

dependencies {
    // CardView
    compile 'com.android.support:cardview-v7:23.3.+'
}

要使用CardView就要在布局文件中添加<android.support.v7.widget.CardView> 然后在节点里面添加其他的UI控件。下面的布局中CardView只有一个简单的TextView。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:card_view="http://schemas.android.com/apk/res-auto">
 
    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card_view"
        android:layout_gravity="center"
        android:layout_width="250dp"
        android:layout_height="250dp"
        card_view:cardCornerRadius="4dp">
 
        <TextView
            android:text="Hello Card"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
 
    </android.support.v7.widget.CardView>
 
</LinearLayout>

1. 创建新项目
   通过 File ⇒ New Project 的方式在Android Studio中创建一个新项目，然后在弹出选择Activity的模板页中选择Empty Activity。

2. 下载 res.zip 然后将其添加到你刚刚创建项目的资源文件夹上，这个资源文件夹中包含了专辑封面以及其他需要的图标。

3. 将下面的字符串，颜色和尺寸资源添加到strings.xml, colors.xml and dimens.xml文件中.

strings.xml

<resources>
    <string name="app_name">Card View</string>
    <string name="action_settings">Settings</string>
    <string name="action_add_favourite">Add to Favourites</string>
    <string name="action_play_next">Play Next</string>
    <string name="backdrop_title">LOVE MUSIC</string>
    <string name="backdrop_subtitle">This season top 20 albums</string>
</resources>

colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#F50057</color>
    <color name="colorPrimaryDark">#F50057</color>
    <color name="colorAccent">#FF4081</color>
    <color name="viewBg">#f1f5f8</color>
    <color name="album_title">#4c4c4c</color>
</resources>

dimens.xml

<resources>
    <!-- Default screen margins, per the Android Design guidelines. -->
    <dimen name="activity_horizontal_margin">16dp</dimen>
    <dimen name="activity_vertical_margin">16dp</dimen>
    <dimen name="fab_margin">16dp</dimen>
    <dimen name="item_offset">10dp</dimen>
    <dimen name="detail_backdrop_height">250dp</dimen>
    <dimen name="backdrop_title">30dp</dimen>
    <dimen name="backdrop_subtitle">18dp</dimen>
    <dimen name="card_margin">5dp</dimen>
    <dimen name="card_album_radius">0dp</dimen>
    <dimen name="album_cover_height">160dp</dimen>
    <dimen name="album_title_padding">10dp</dimen>
    <dimen name="album_title">15dp</dimen>
    <dimen name="songs_count_padding_bottom">5dp</dimen>
    <dimen name="songs_count">12dp</dimen>
    <dimen name="ic_album_overflow_width">20dp</dimen>
    <dimen name="ic_album_overflow_height">30dp</dimen>
    <dimen name="ic_album_overflow_margin_top">10dp</dimen>
</resources>

4. 打开 build.gradle 往上面添加CardView, RecyclerView 和 Glide 的依赖. RecyclerView 用于以网格的方式显示专辑信息，CardView 用于现实单个专辑信息，Glide用于显示专辑封面图片。

build.gradle
dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'
    compile 'com.android.support:design:23.3.0'
    // RecyclerView
    compile 'com.android.support:recyclerview-v7:23.3.+'
    // CardView
    compile 'com.android.support:cardview-v7:23.3.+'
    // Glide
    compile 'com.github.bumptech.glide:glide:3.7.0'
}

5. 为了创建单个专辑的实例，我们使用一个单独的model类来存放专辑姓名，歌曲数目和封面图片，下面是这个类的源码：
   Abum.java

   package info.androidhive.cardview;
   public class Album {
       private String name;
       private int numOfSongs;
       private int thumbnail; 
       public Album() {
       }
       public Album(String name, int numOfSongs, int thumbnail) {
           this.name = name;
           this.numOfSongs = numOfSongs;
           this.thumbnail = thumbnail;
       }
       public String getName() {
           return name;
       }
       public void setName(String name) {
           this.name = name;
       }
       public int getNumOfSongs() {
           return numOfSongs;
       }
       public void setNumOfSongs(int numOfSongs) {
           this.numOfSongs = numOfSongs;
       }
       public int getThumbnail() {
           return thumbnail;
       }
       public void setThumbnail(int thumbnail) {
           this.thumbnail = thumbnail;
       }
   }

6. 我们还需要一个xml布局文件用于现实专辑卡片，这里我们新建一个album_card.xml 布局文件，这里我们增加了<android.support.v7.widget.CardView> 并且添加了专辑姓名，歌曲数目，和专辑封面等信息。并且我们还添加了三个点的按钮，在我们按下它的时候会弹出Popup 菜单。

album_card.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <android.support.v7.widget.CardView
        android:id="@+id/card_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:layout_margin="@dimen/card_margin"
        android:elevation="3dp"
        card_view:cardCornerRadius="@dimen/card_album_radius">
        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <ImageView
                android:id="@+id/thumbnail"
                android:layout_width="match_parent"
                android:layout_height="@dimen/album_cover_height"
                android:background="?attr/selectableItemBackgroundBorderless"
                android:clickable="true"
                android:scaleType="fitXY" />
            <TextView
                android:id="@+id/title"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_below="@id/thumbnail"
                android:paddingLeft="@dimen/album_title_padding"
                android:paddingRight="@dimen/album_title_padding"
                android:paddingTop="@dimen/album_title_padding"
                android:textColor="@color/album_title"
                android:textSize="@dimen/album_title" />
            <TextView
                android:id="@+id/count"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_below="@id/title"
                android:paddingBottom="@dimen/songs_count_padding_bottom"
                android:paddingLeft="@dimen/album_title_padding"
                android:paddingRight="@dimen/album_title_padding"
                android:textSize="@dimen/songs_count" />
            <ImageView
                android:id="@+id/overflow"
                android:layout_width="@dimen/ic_album_overflow_width"
                android:layout_height="@dimen/ic_album_overflow_height"
                android:layout_alignParentRight="true"
                android:layout_below="@id/thumbnail"
                android:layout_marginTop="@dimen/ic_album_overflow_margin_top"
                android:scaleType="centerCrop"
                android:src="@drawable/ic_dots" />
        </RelativeLayout>
    </android.support.v7.widget.CardView>
</LinearLayout>

7. 创建一个menu文件，这个menu将会在用户点击弹出菜单的按钮的时候作为菜单显现出来的。

   menu_album.xml
   <menu 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">
       <item
           android:id="@+id/action_add_favourite"
           android:orderInCategory="100"
           android:title="@string/action_add_favourite" />
       <item
           android:id="@+id/action_play_next"
           android:orderInCategory="101"
           android:title="@string/action_play_next" />
   </menu>

8. 为了使用RectycleView我们需要一个Adapter类它通过将有用的数据inflates album_card.xml 布局.因此我们需要创建一个AlbumsAdapter.java的类然后添加如下的内容：

AlbumsAdapter.java

package info.androidhive.cardview;
import android.content.Context;
import android.support.v7.widget.PopupMenu;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.bumptech.glide.Glide;
import java.util.List;
public class AlbumsAdapter extends RecyclerView.Adapter<AlbumsAdapter.MyViewHolder> {
    private Context mContext;
    private List<Album> albumList;
    public class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView title, count;
        public ImageView thumbnail, overflow;
        public MyViewHolder(View view) {
            super(view);
            title = (TextView) view.findViewById(R.id.title);
            count = (TextView) view.findViewById(R.id.count);
            thumbnail = (ImageView) view.findViewById(R.id.thumbnail);
            overflow = (ImageView) view.findViewById(R.id.overflow);
        }
    }
    public AlbumsAdapter(Context mContext, List<Album> albumList) {
        this.mContext = mContext;
        this.albumList = albumList;
    }
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.album_card, parent, false);
        return new MyViewHolder(itemView);
    }
    @Override
    public void onBindViewHolder(final MyViewHolder holder, int position) {
        Album album = albumList.get(position);
        holder.title.setText(album.getName());
        holder.count.setText(album.getNumOfSongs() + " songs");
        // loading album cover using Glide library
        Glide.with(mContext).load(album.getThumbnail()).into(holder.thumbnail);
        holder.overflow.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showPopupMenu(holder.overflow);
            }
        });
    }
    /**
     * Showing popup menu when tapping on 3 dots
     */
    private void showPopupMenu(View view) {
        // inflate menu
        PopupMenu popup = new PopupMenu(mContext, view);
        MenuInflater inflater = popup.getMenuInflater();
        inflater.inflate(R.menu.menu_album, popup.getMenu());
        popup.setOnMenuItemClickListener(new MyMenuItemClickListener());
        popup.show();
    }
    /**
     * Click listener for popup menu items
     */
    class MyMenuItemClickListener implements PopupMenu.OnMenuItemClickListener {
        public MyMenuItemClickListener() {
        }
        @Override
        public boolean onMenuItemClick(MenuItem menuItem) {
            switch (menuItem.getItemId()) {
                case R.id.action_add_favourite:
                    Toast.makeText(mContext, "Add to favourite", Toast.LENGTH_SHORT).show();
                    return true;
                case R.id.action_play_next:
                    Toast.makeText(mContext, "Play next", Toast.LENGTH_SHORT).show();
                    return true;
                default:
            }
            return false;
        }
    }
    @Override
    public int getItemCount() {
        return albumList.size();
    }
}

9. 打卡main Activity 的布局文件activity_main.xml和content_main 添加AppBarLayout, CollapsingToolbarLayout, Toolbar and RecyclerView.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white"
    android:fitsSystemWindows="true">
    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/detail_backdrop_height"
        android:fitsSystemWindows="true"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:expandedTitleMarginEnd="64dp"
            app:expandedTitleMarginStart="48dp"
            app:expandedTitleTextAppearance="@android:color/transparent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed">
            <RelativeLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">
                <ImageView
                    android:id="@+id/backdrop"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:fitsSystemWindows="true"
                    android:scaleType="centerCrop"
                    app:layout_collapseMode="parallax" />
                <LinearLayout
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_centerInParent="true"
                    android:gravity="center_horizontal"
                    android:orientation="vertical">
                    <TextView
                        android:id="@+id/love_music"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:text="@string/backdrop_title"
                        android:textColor="@android:color/white"
                        android:textSize="@dimen/backdrop_title" />
                    <TextView
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:text="@string/backdrop_subtitle"
                        android:textColor="@android:color/white"
                        android:textSize="@dimen/backdrop_subtitle" />
                </LinearLayout>
            </RelativeLayout>
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>
    <include layout="@layout/content_main" />
</android.support.design.widget.CoordinatorLayout>

content_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:background="@color/viewBg"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="info.androidhive.cardview.MainActivity"
    tools:showIn="@layout/activity_main">
    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:clipToPadding="false"
        android:scrollbars="vertical" />
</RelativeLayout>

10.最后打开MainActivity.java 做一些必要的修改.

• initCollapsingToolbar() 在toolbar展开或者合上的时候显示或者隐藏toolbar。
• prepareAlbums() 添加RecycleView所需要的样本专辑数据。
• GridLayoutManager 用于将RecyclerView 以网格的方式显示出来。
• GridSpacingItemDecoration 用于添加RecycleView网格item的空白边界。
• AlbumsAdapter 创建后将分配给RecycleViewm,RecycleView通过网格的形式将其显示出来。MainActivity.java

  package info.androidhive.cardview;
  import android.content.res.Resources;
  import android.graphics.Rect;
  import android.os.Bundle;
  import android.support.design.widget.AppBarLayout;
  import android.support.design.widget.CollapsingToolbarLayout;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.DefaultItemAnimator;
  import android.support.v7.widget.GridLayoutManager;
  import android.support.v7.widget.RecyclerView;
  import android.support.v7.widget.Toolbar;
  import android.util.TypedValue;
  import android.view.View;
  import android.widget.ImageView;
  import com.bumptech.glide.Glide;
  import java.util.ArrayList;
  import java.util.List;
  public class MainActivity extends AppCompatActivity {
      private RecyclerView recyclerView;
      private AlbumsAdapter adapter;
      private List<Album> albumList;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
          initCollapsingToolbar();
          recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
          albumList = new ArrayList<>();
          adapter = new AlbumsAdapter(this, albumList);
          RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(this, 2);
          recyclerView.setLayoutManager(mLayoutManager);
          recyclerView.addItemDecoration(new GridSpacingItemDecoration(2, dpToPx(10), true));
          recyclerView.setItemAnimator(new DefaultItemAnimator());
          recyclerView.setAdapter(adapter);
          prepareAlbums();
          try {
              Glide.with(this).load(R.drawable.cover).into((ImageView) findViewById(R.id.backdrop));
          } catch (Exception e) {
              e.printStackTrace();
          }
      }
      /**
       * Initializing collapsing toolbar
       * Will show and hide the toolbar title on scroll
       */
      private void initCollapsingToolbar() {
          final CollapsingToolbarLayout collapsingToolbar =
          (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);
          collapsingToolbar.setTitle(" ");
          AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.appbar);
          appBarLayout.setExpanded(true);
          appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
              boolean isShow = false;
              int scrollRange = -1;
              @Override
              public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                  if (scrollRange == -1) {
                      scrollRange = appBarLayout.getTotalScrollRange();
                  }
                  if (scrollRange + verticalOffset == 0) {
                      collapsingToolbar.setTitle(getString(R.string.app_name));
                      isShow = true;
                  } else if (isShow) {
                      collapsingToolbar.setTitle(" ");
                      isShow = false;
                  }
              }
          });
      }
      /**
       * Adding few albums for testing
       */
      private void prepareAlbums() {
          int[] covers = new int[]{
                  R.drawable.album1,
                  R.drawable.album2,
                  R.drawable.album3,
                  R.drawable.album4,
                  R.drawable.album5,
                  R.drawable.album6,
                  R.drawable.album7,
                  R.drawable.album8,
                  R.drawable.album9,
                  R.drawable.album10,
                  R.drawable.album11};
          Album a = new Album("True Romance", 13, covers[0]);
          albumList.add(a);
          a = new Album("Xscpae", 8, covers[1]);
          albumList.add(a);
          a = new Album("Maroon 5", 11, covers[2]);
          albumList.add(a);
          a = new Album("Born to Die", 12, covers[3]);
          albumList.add(a);
          a = new Album("Honeymoon", 14, covers[4]);
          albumList.add(a);
          a = new Album("I Need a Doctor", 1, covers[5]);
          albumList.add(a);
          a = new Album("Loud", 11, covers[6]);
          albumList.add(a);
          a = new Album("Legend", 14, covers[7]);
          albumList.add(a);
          a = new Album("Hello", 11, covers[8]);
          albumList.add(a);
          a = new Album("Greatest Hits", 17, covers[9]);
          albumList.add(a);
          adapter.notifyDataSetChanged();
      }
      /**
       * RecyclerView item decoration - give equal margin around grid item
       */
      public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {
          private int spanCount;
          private int spacing;
          private boolean includeEdge;
          public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge) {
              this.spanCount = spanCount;
              this.spacing = spacing;
              this.includeEdge = includeEdge;
          }
          @Override
          public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
              int position = parent.getChildAdapterPosition(view); // item position
              int column = position % spanCount; // item column
              if (includeEdge) {
                  outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                  outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)
                  if (position < spanCount) { // top edge
                      outRect.top = spacing;
                  }
                  outRect.bottom = spacing; // item bottom
              } else {
                  outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                  outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                  if (position >= spanCount) {
                      outRect.top = spacing; // item top
                  }
              }
          }
      }
   
      /**
       * Converting dp to pixel
       */
      private int dpToPx(int dp) {
          Resources r = getResources();
          return Math.round(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics()));
      }
  }