Android中使用RecyclerView和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>