介紹
RecyclerView是ListView的豪華增強版。它主要包含以下幾處新的特性,如ViewHolder,ItemDecorator,LayoutManager,SmothScroller以及增加或删除item時item動畫等。官方推薦我們采用RecyclerView來取代ListView。
相對優勢
-
ViewHolder
ListView需要自己實作ViewHolder來提高性能,或者不使用ViewHolder,但是使用ViewHolder來綁定對象是一個很好的習慣。RecyclerView很好的幫我們解決了這個問題,RecyclerView.ViewHolder在使用RecyclerView過程中必須實作,因為它是一個抽象類無法直接建立,需要自己完成對應子類的建立然後使用
-
LayoutManager
ListView隻能在垂直方向上滾動,不支援其他的滾動方式,當然開發者有很多自定義的方式完成這些功能,這裡就不做争辯,從設計的角度上看,ListView設計之初應該就沒有想過讓它完成這些複雜的功能,隻是為了單純的清單顯示。但是RecyclerView相較于ListView,在滾動上面的功能擴充了許多。它可以支援多種類型清單的展示要求,主要如下:
GridLayoutManager ,支援網格展示,可以水準或者豎直滾動,如展示圖檔的畫廊。
LinearLayoutManager ,可以支援水準和豎直方向上滾動的清單。
StaggeredGridLayoutManager ,可以支援交叉網格風格的清單,類似于瀑布流或者Pinterest。
-
ItemAnimation
ItemAnimation是RecyclerView中子項在增加,删除或者移動的情況下顯示的動畫效果,Google越來越重視使用者體驗,從屬性動畫的推出開始,這就是一個趨勢,開發者在這裡可以自己實作自己想要添加的動畫效果,當然,如果你是個懶漢,請使用new DefaultItemAnimator() 。
-
ItemDecoration
ItemDecoration,名字起的很文藝,子項的裝飾,RecyclerView在預設情況下并不在item之間展示間隔符。如果你想要添加間隔符,你必須使用RecyclerView.ItemDecoration類來實作。懶漢請使用DividerItemDecoration.java。
Recycler示例
實際效果圖
上面這個效果圖是使用的StaggeredGridLayoutManager
代碼層面
布局檔案
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對應的Adapter
private ArrayList<String> mContentList; //内容list這裡隻是使用了字元串,當然也可以替換成其他的JavaBean類
private Random mRandom = new Random(); //用于産生随機字元串
private int mSum = 50; //初始化子項數目
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this); //ButterKnife注入,減少代碼負擔
mContentList = new ArrayList<String>();
for (int i = 0; i < mSum; i++) {
mContentList.add(getRandomString());
} //随機生成資料
recyclerAdapter = new RVAdapter(mContentList);
mLayoutManager = new StaggeredGridLayoutManager(3, LinearLayoutManager.VERTICAL); //3列縱向
rvContent.setAdapter(recyclerAdapter);
rvContent.setLayoutManager(mLayoutManager);
rvContent.setItemAnimator(new DefaultItemAnimator()); //設定動畫效果,可以看下上面的效果圖,動畫效果還是比較明顯的
}
@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); //加一個
makeSnackBar(rootLayout, "添加一個 :)", null, null);//顯示一個Snackbar
break;
case R.id.fab_del:
recyclerAdapter.removeData(1); //去掉一個
makeSnakeBar(rootLayout, "删除一個 :(", null, null); //顯示一個Snackbar
break;
default:
break;
}
}
//用于産生随機字元串的方法
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();
}
//建構一個Snackbar并顯示出來
private void makeSnackBar(View view, String message, String buttonText, View.OnClickListener onClickListener) {
Snackbar.make(view, message, Snackbar.LENGTH_SHORT)
.setAction(buttonText, onClickListener)
.show();
}
}
擴充卡
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.MyViewHolder>{
ArrayList<String> mContentList;
Random mRandom = new Random();
//ViewHolder繼承自RecyclerView.ViewHolder 子View拿到友善後面通路
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;
}
//建立ViewHolder,由于RecyclerView.ViewHolder是一個抽象類無法執行個體化,是以必須實作一個子類才能使用,這裡自己嘗試的過程中走了一些彎路,注意inflate最後一個參數設定成false不然可能會出現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 用于設定需要顯示的View中的内容和一些屬性值
@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);//産生随機高度,看上去像瀑布
}
@Override
public int getItemCount() {
return mContentList.size();
}
//産生随機顔色
private int getRandomColor() {
return (0xff000000|mRandom.nextInt(0x00ffffff));
}
//産生随機高度
private int getRandomHeight(int min , int max) {
return (mRandom.nextInt(max - min) + min );
}
//添加一個子項
public void addData(int position) {
mContentList.add(position, "Insert One");
notifyItemInserted(position);//不調用這個沒有動畫效果
}
//删除一個子項
public void removeData(int position) {
mContentList.remove(position);
notifyItemRemoved(position);//不調用這個沒有動畫效果
}
}
需要注意的幾個地方:
- 實作自己的ViewHolder繼承recyclerView,ViewHolder,因為抽象類不能執行個體化
- inflate子項的時候,最後一個參數設定成false
- 動畫效果需要在Adapter中調用notifyItem***方法才行
StaggeredGridLayoutManager的效果圖上面已經有顯示了
其他效果
LinearLayoutManager效果圖
對應修改代碼
mLayoutManager = new LinearLayoutManager(this);
rvContent.addItemDecoration(new DividerItemDecoration(this, StaggeredGridLayoutManager.VERTICAL));
GridLayoutManager效果圖
對應修改代碼
mLayoutManager = new GridLayoutManager(this, 3);//3列
rvContent.addItemDecoration(new DividerItemDecoration(this, StaggeredGridLayoutManager.VERTICAL));
StaggeredGridLayoutManager.HORIZONTAL橫向的效果圖
對應修改代碼
mLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.HORIZONTAL);
RVAdapter.java中onBindViewHolder
holder.itemView.getLayoutParams().width = getRandomHeight(200,400);
關于ItemDecoration
這裡附上Google Sample中的DividerItemDecoration.java代碼 希望可以幫助到大家
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);
}
}
}
備注
Android源碼中有很多關于這些View的使用方法,大家可以查閱并參考使用。
博文中部分代碼:
http://download.csdn.net/detail/poorkick/9541326