介绍
RecyclerView是ListView的豪华增强版。它主要包含以下几处新的特性,如ViewHolder,ItemDecorator,LayoutManager,SmothScroller以及增加或删除item时item动画等。官方推荐我们采用RecyclerView来取代ListView。
相对优势
- ViewHolder
ListView需要自己实现ViewHolder来提高性能,或者不使用ViewHolder,但是使用ViewHolder来绑定对象是一个很好的习惯。RecyclerView很好的帮我们解决了这个问题,RecyclerView.ViewHolder在使用RecyclerView过程中必须实现,因为它是一个抽象类无法直接创建,需要自己完成对应子类的建立然后使用
- LayoutManager
ListView只能在垂直方向上滚动,不支持其他的滚动方式,当然开发者有很多自定义的方式完成这些功能,这里就不做争辩,从设计的角度上看,ListView设计之初应该就没有想过让它完成这些复杂的功能,只是为了单纯的列表显示。但是RecyclerView相较于ListView,在滚动上面的功能扩展了许多。它可以支持多种类型列表的展示要求,主要如下:
GridLayoutManager ,支持网格展示,可以水平或者竖直滚动,如展示图片的画廊。
LinearLayoutManager ,可以支持水平和竖直方向上滚动的列表。
StaggeredGridLayoutManager ,可以支持交叉网格风格的列表,类似于瀑布流或者Pinterest。
- ItemAnimation
ItemAnimation是RecyclerView中子项在增加,删除或者移动的情况下显示的动画效果,Google越来越重视用户体验,从属性动画的推出开始,这就是一个趋势,开发者在这里可以自己实现自己想要添加的动画效果,当然,如果你是个懒汉,请使用new DefaultItemAnimator() 。
- ItemDecoration
ItemDecoration,名字起的很文艺,子项的装饰,RecyclerView在默认情况下并不在item之间展示间隔符。如果你想要添加间隔符,你必须使用RecyclerView.ItemDecoration类来实现。懒汉请使用DividerItemDecoration.java。
Recycler示例
实际效果图
上面这个效果图是使用的StaggeredGridLayoutManager
代码层面
布局文件
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/root_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@color/colorMainBackground">
<include layout="@layout/toolbar"></include>
<FrameLayout 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"
tools:context=".model.View.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/rv_content"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab_add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|right"
android:layout_marginBottom="30dp"
android:layout_marginRight="30dp"
android:src="@drawable/addone" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab_del"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|left"
android:layout_marginBottom="30dp"
android:layout_marginLeft="30dp"
android:src="@drawable/delone" />
</FrameLayout>
</LinearLayout>
recycler_item.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto">
<android.support.v7.widget.CardView
android:layout_margin="10dp"
android:id="@+id/cv_bg"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:cardCornerRadius="20dp"
app:cardElevation="5dp">
<TextView
android:id="@+id/tv_name"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center" />
</android.support.v7.widget.CardView>
</FrameLayout>
主Activity
public class MainActivity extends AppCompatActivity {
@Bind(R.id.rv_content)
RecyclerView rvContent;
@Bind(R.id.fab_add)
FloatingActionButton fabAdd;
@Bind(R.id.fab_del)
FloatingActionButton fabDel;
@Bind(R.id.root_layout)
LinearLayout rootLayout;
private LayoutManager mLayoutManager; //LayoutManager
private RVAdapter recyclerAdapter; //RecyclerView对应的Adapter
private ArrayList<String> mContentList; //内容list这里只是使用了字符串,当然也可以替换成其他的JavaBean类
private Random mRandom = new Random(); //用于产生随机字符串
private int mSum = 50; //初始化子项数目
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this); //ButterKnife注入,减少代码负担
mContentList = new ArrayList<String>();
for (int i = 0; i < mSum; i++) {
mContentList.add(getRandomString());
} //随机生成数据
recyclerAdapter = new RVAdapter(mContentList);
mLayoutManager = new StaggeredGridLayoutManager(3, LinearLayoutManager.VERTICAL); //3列纵向
rvContent.setAdapter(recyclerAdapter);
rvContent.setLayoutManager(mLayoutManager);
rvContent.setItemAnimator(new DefaultItemAnimator()); //设置动画效果,可以看下上面的效果图,动画效果还是比较明显的
}
@OnClick({R.id.fab_add, R.id.fab_del})
public void onClick(View view) {
switch (view.getId()) {
case R.id.fab_add:
recyclerAdapter.addData(1); //加一个
makeSnackBar(rootLayout, "添加一个 :)", null, null);//显示一个Snackbar
break;
case R.id.fab_del:
recyclerAdapter.removeData(1); //去掉一个
makeSnakeBar(rootLayout, "删除一个 :(", null, null); //显示一个Snackbar
break;
default:
break;
}
}
//用于产生随机字符串的方法
public String getRandomString() {
String src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
StringBuilder dst = new StringBuilder(4);
for (int i = 0; i < 4; i++) {
dst.append(src.charAt(mRandom.nextInt(62)));
}
return dst.toString();
}
//构建一个Snackbar并显示出来
private void makeSnackBar(View view, String message, String buttonText, View.OnClickListener onClickListener) {
Snackbar.make(view, message, Snackbar.LENGTH_SHORT)
.setAction(buttonText, onClickListener)
.show();
}
}
适配器
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.MyViewHolder>{
ArrayList<String> mContentList;
Random mRandom = new Random();
//ViewHolder继承自RecyclerView.ViewHolder 子View拿到方便后面访问
public class MyViewHolder extends RecyclerView.ViewHolder {
TextView textView;
CardView cardView;
public MyViewHolder(View itemView) {
super(itemView);
textView = (TextView) itemView.findViewById(R.id.tv_name);
cardView = (CardView) itemView.findViewById(R.id.cv_bg);
}
}
public RVAdapter(ArrayList<String> mContentList) {
this.mContentList = mContentList;
}
//创建ViewHolder,由于RecyclerView.ViewHolder是一个抽象类无法实例化,所以必须实现一个子类才能使用,这里自己尝试的过程中走了一些弯路,注意inflate最后一个参数设置成false不然可能会出现crash
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_item, parent, false);
return new MyViewHolder(view);
}
//onBindView 用于设置需要显示的View中的内容和一些属性值
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.cardView.setCardBackgroundColor(getRandomColor());
holder.textView.setText(mContentList.get(position));
holder.itemView.getLayoutParams().height = getRandomHeight(200,400);//产生随机高度,看上去像瀑布
}
@Override
public int getItemCount() {
return mContentList.size();
}
//产生随机颜色
private int getRandomColor() {
return (0xff000000|mRandom.nextInt(0x00ffffff));
}
//产生随机高度
private int getRandomHeight(int min , int max) {
return (mRandom.nextInt(max - min) + min );
}
//添加一个子项
public void addData(int position) {
mContentList.add(position, "Insert One");
notifyItemInserted(position);//不调用这个没有动画效果
}
//删除一个子项
public void removeData(int position) {
mContentList.remove(position);
notifyItemRemoved(position);//不调用这个没有动画效果
}
}
需要注意的几个地方:
1. 实现自己的ViewHolder继承recyclerView,ViewHolder,因为抽象类不能实例化
2. inflate子项的时候,最后一个参数设置成false
3. 动画效果需要在Adapter中调用notifyItem***方法才行
StaggeredGridLayoutManager的效果图上面已经有显示了
其他效果
LinearLayoutManager效果图
对应修改代码
mLayoutManager = new LinearLayoutManager(this);
rvContent.addItemDecoration(new DividerItemDecoration(this, StaggeredGridLayoutManager.VERTICAL));
GridLayoutManager效果图
对应修改代码
mLayoutManager = new GridLayoutManager(this, 3);//3列
rvContent.addItemDecoration(new DividerItemDecoration(this, StaggeredGridLayoutManager.VERTICAL));
StaggeredGridLayoutManager.HORIZONTAL横向的效果图
对应修改代码
mLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.HORIZONTAL);
RVAdapter.java中onBindViewHolder
holder.itemView.getLayoutParams().width = getRandomHeight(200,400);
关于ItemDecoration
这里附上Google Sample中的DividerItemDecoration.java代码 希望可以帮助到大家
public class DividerItemDecoration extends RecyclerView.ItemDecoration {
private static final int[] ATTRS = new int[]{
android.R.attr.listDivider
};
public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;
public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;
private Drawable mDivider;
private int mOrientation;
public DividerItemDecoration(Context context, int orientation) {
final TypedArray a = context.obtainStyledAttributes(ATTRS);
mDivider = a.getDrawable(0);
a.recycle();
setOrientation(orientation);
}
public void setOrientation(int orientation) {
if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
throw new IllegalArgumentException("invalid orientation");
}
mOrientation = orientation;
}
@Override
public void onDraw(Canvas c, RecyclerView parent) {
if (mOrientation == VERTICAL_LIST) {
drawVertical(c, parent);
} else {
drawHorizontal(c, parent);
}
}
public void drawVertical(Canvas c, RecyclerView parent) {
final int left = parent.getPaddingLeft();
final int right = parent.getWidth() - parent.getPaddingRight();
final int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
final View child = parent.getChildAt(i);
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
.getLayoutParams();
final int top = child.getBottom() + params.bottomMargin +
Math.round(ViewCompat.getTranslationY(child));
final int bottom = top + mDivider.getIntrinsicHeight();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
public void drawHorizontal(Canvas c, RecyclerView parent) {
final int top = parent.getPaddingTop();
final int bottom = parent.getHeight() - parent.getPaddingBottom();
final int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
final View child = parent.getChildAt(i);
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
.getLayoutParams();
final int left = child.getRight() + params.rightMargin +
Math.round(ViewCompat.getTranslationX(child));
final int right = left + mDivider.getIntrinsicHeight();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
@Override
public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
if (mOrientation == VERTICAL_LIST) {
outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
} else {
outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
}
}
}
备注
Android源码中有很多关于这些View的使用方法,大家可以查阅并参考使用。
博文中部分代码:
http://download.csdn.net/detail/poorkick/9541001