Android中使用RecyclerView跟CardView实现瀑布流效果(StaggeredGrid)

在Android 5.0 中引入了Material Design的设计理念，并加入了RecyclerView和CardView两个控件。本文就讲解如何使用者两个控件来实现瀑布流效果(StaggeredGrid)。

先上效果图

RecyclerView

RecyclerView 是一个更加高级和灵活的ListView。它简化了显示和处理数据的过程，比如，为positioning item提供了layout 的管理，为item删除和添加提供了默认的动画。当然，你也可以自定义这些动画。

LayoutManger决定RecyclerView中元素的位置和何时重用那些不再显示的item。LayoutManager通过避免创建不必要的view和不调用费时的findViewById() 来提高效率。
RecyclerView提供了三种内建的LayoutManger：

• LinearLayoutManager 垂直或者水平的可以滑动的list
• GridLayoutManager 以grid的方式显示
• StaggeredGridLayoutManager 以瀑布流的形式显示（本文重点 (⊙v⊙)嗯）

动画

RecyclerView是有默认的添加删除item的动画的，如果想要自定义这些动画，继承RecyclerView.ItemAnimator 这个类，并使用RecyclerView.setItemAnimator() 这个方法。

例子

activity_recycler_view.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.example.daniel.test.activities.RecyclerViewActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/my_recycler_view"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

view_holder.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <ImageView
        android:id="@+id/iv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

Activity

public class RecyclerViewActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;
    private String[] myDataset = {"1", "2", "3", "4", "5", "6", "7"};

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

        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        mRecyclerView.setHasFixedSize(true);

        // use a linear layout manager
        mLayoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(mLayoutManager);

        // specify an adapter (see also next example)
        mAdapter = new MyAdapter(myDataset);
        mRecyclerView.setAdapter(mAdapter);
    }

}

这里的Adaper是一个数据和UI之间的桥梁，把数据显示在UI上。
下面一个例子是一个简单的Adapter实现。

class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private String[] mDataset;

    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public static class ViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        public ImageView mImageView;
        public TextView mTextView;

        public ViewHolder(View v) {
            super(v);
            mTextView = (TextView) v.findViewById(R.id.tv_title);
            mImageView = (ImageView) v.findViewById(R.id.iv_title);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(String[] myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_holder, parent, false);
        // set the view's size, margins, paddings and layout parameters
        //TO-DO

        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element
        holder.mImageView.setImageResource(R.mipmap.ic_launcher);
        holder.mTextView.setText(mDataset[position]);

    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

关于RecyclerView.Adapter 的说明:

以下三个方法是必须要实现的。
- onCreateViewHolder 返回每一个Item的ViewHolder
- onBindViewHolder 给Item中的控件赋值
- getItemCount 返回Item的个数

效果

CardView

CardView继承自FrameLayout，利用它可以使你的信息在卡片中显示，并且在不同的平台中具有一致性。
利用以下的属性可以自定义CardView的外观：
card_view:cardCornerRadius 设置圆角的半径
CardView.setRadius 在代码中设置圆角的半径
card_view:cardBackgroundColor 设置卡片的背景

例子

<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"
    ... >
    <!-- A CardView that contains a TextView -->
    <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="200dp"
        android:layout_height="200dp"
        card_view:cardCornerRadius="4dp">

        <TextView
            android:id="@+id/info_text"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </android.support.v7.widget.CardView>
</LinearLayout>

依赖的包

RecyclerView 和 CardView是v7 Support Libraries的一部分，所以需要在你app的Gradle dependencies 里加入以下内容：

dependencies {
…
compile ‘com.android.support:cardview-v7:21.0.+’
compile ‘com.android.support:recyclerview-v7:21.0.+’
}

实现瀑布流效果(StaggeredGrid)

效果

activity_recycler_view.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.example.daniel.test.activities.RecyclerViewActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/my_recycler_view"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

Activity

public class RecyclerViewActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;
    private String[] myDataset = {"1", "2", "3", "4", "5", "6", "7","1", "2", "3", "4", "5", "6", "7"};

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

        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        mRecyclerView.setHasFixedSize(true);

        // use a linear layout manager
        mLayoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(mLayoutManager);

        // specify an adapter (see also next example)
        mAdapter = new MyAdapter(myDataset);
        mRecyclerView.setAdapter(mAdapter);
    }

}

class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private String[] mDataset;

    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public static class ViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        public ImageView mImageView;
        public TextView mTextView;

        public ViewHolder(View v) {
            super(v);
            mTextView = (TextView) v.findViewById(R.id.tv_title);
            mImageView = (ImageView) v.findViewById(R.id.iv_title);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(String[] myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_holder, parent, false);
        // set the view's size, margins, paddings and layout parameters
        //TO-DO

        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element
        if(position %2 == 0) {
            holder.mImageView.setImageResource(R.drawable.icon);
        }
        else {
            holder.mImageView.setImageResource(R.mipmap.ic_launcher);
        }
        holder.mTextView.setText(mDataset[position]);

    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

class TestAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder>{

    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return null;
    }

    @Override
    public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {

    }

    @Override
    public int getItemCount() {
        return 0;
    }
}

ViewHolder

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/tools"
    android:orientation="horizontal"
    android:padding="4dp"
    >

    <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card_view"
        android:layout_width="140dp"
        android:layout_height="match_parent"
        android:layout_gravity="center_vertical"
        app:cardUseCompatPadding="true"
        card_view:cardCornerRadius="10dp">

        <TextView
            android:id="@+id/tv_title"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:textSize="25sp"
            android:layout_gravity="center_vertical"
            android:gravity="center_vertical"
            android:textColor="#ffffff"
            android:background="#1976D2"
            />

        <ImageView
            android:id="@+id/iv_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"/>
    </android.support.v7.widget.CardView>

</LinearLayout>