Android 5.0引入了一個(gè)全新的列表控件-RecyclerView，這個(gè)控件更為靈活，同時(shí)也擁有比ListView和GridView控件較多的優(yōu)點(diǎn)：例如Item View的創(chuàng)建、View的回收以及重用等機(jī)制。
RecyclerView控件提供了以下兩種方法來(lái)進(jìn)行簡(jiǎn)化和處理大數(shù)量集合:
可以自定義LayoutManager或者設(shè)置添加/刪除的動(dòng)畫(huà)，整體的RecyclerView結(jié)構(gòu)圖如下:
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-1.png" alt="這里寫(xiě)圖片描述" />
為了使用RecyclerView控件，需要?jiǎng)?chuàng)建一個(gè)Adapter和一個(gè)LayoutManager類(lèi)，Adapter：繼承自RecyclerView.Adapetr類(lèi)，主要用來(lái)將數(shù)據(jù)和布局item進(jìn)行綁定。LayoutManager:布局管理器，設(shè)置每一項(xiàng)view在RecyclerView中的位置布局以及控件item view的顯示或者隱藏.當(dāng)View重用或者回收的時(shí)候，LayoutManger都會(huì)向Adapter來(lái)請(qǐng)求新的數(shù)據(jù)來(lái)進(jìn)行替換原來(lái)數(shù)據(jù)的內(nèi)容。這種回收重用的機(jī)制可以提供性能，避免創(chuàng)建很多的view或者是頻繁的調(diào)用findViewById方法。這種機(jī)制和ListView還是很相似的。
RecyclerView提供了三種內(nèi)置的LayoutManager:
當(dāng)然除了上面的三種內(nèi)部布局之外，我們還可以繼承RecyclerView.LayoutManager來(lái)實(shí)現(xiàn)一個(gè)自定義的LayoutManager。 RecyclerView對(duì)于Item的添加和刪除是默認(rèn)開(kāi)啟動(dòng)畫(huà)的。我們當(dāng)然也可以通過(guò)RecyclerView.ItemAnimator類(lèi)定制動(dòng)畫(huà)，然后通過(guò)RecyclerView.setItemAnimator()方法來(lái)進(jìn)行使用。 RecyclerView常用類(lèi):
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-2.png" alt="這里寫(xiě)圖片描述" />
下面通過(guò)一個(gè)簡(jiǎn)單實(shí)例對(duì)RecyclerView有一個(gè)簡(jiǎn)單的理解。 主布局文件代碼（activity_main.xml）：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycleview"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical" />
</RelativeLayout>注意要引入V7的包才能使用RecyclerView控件，如下圖：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-4.png" alt="這里寫(xiě)圖片描述" />
主布局文件代碼（item.xml）：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="50dp">
<TextView
android:id="@+id/id_num"
android:layout_width="match_parent"
android:layout_height="50dp"
android:gravity="center"
android:text="1" />
</RelativeLayout>這個(gè)是RecyclerView子Item的布局文件。 適配器類(lèi)代碼（MyAdapter.java）：
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
private Context context;
private List<String> datas;
public MyAdapter(Context context,List<String> datas){
this.context=context;
this.datas=datas;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
MyViewHolder holder = new MyViewHolder(LayoutInflater.from(
context).inflate(R.layout.item, parent,
false));
return holder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.tv.setText(datas.get(position));
}
@Override
public int getItemCount() {
return datas.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView tv;
public MyViewHolder(View view) {
super(view);
tv = (TextView) view.findViewById(R.id.id_num);
}
}適配器類(lèi)繼承自RecyclerView.Adapter，這里有幾個(gè)方法需要解釋一下其用法：
MainActivity代碼（MainActivity.java）：
public class MainActivity extends Activity {
private RecyclerView mRecyclerView;
private List<String> mDatas;
private MyAdapter myAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
mRecyclerView = (RecyclerView) findViewById(R.id.recycleview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mRecyclerView.setAdapter(myAdapter = new MyAdapter(this,mDatas));
}
protected void initData() {
mDatas = new ArrayList<String>();
for (int i = 1; i < 20; i++) {
mDatas.add("" + i);
}
}
}initData方法初始化了19條數(shù)據(jù)，setLayoutManger方法設(shè)置RecyclerView的排版方式，一般有三種：
運(yùn)行項(xiàng)目實(shí)例如下：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-3.png" alt="這里寫(xiě)圖片描述" />
我們可以看到，默認(rèn)是不顯示item之間的分割線的，添加分割線的方法比較固定，下面講解一下如何實(shí)現(xiàn)。
這里需要一個(gè)DividerItemDecoration類(lèi)：
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);
RecyclerView v = new RecyclerView(
parent.getContext());
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
.getLayoutParams();
final int top = child.getBottom() + params.bottomMargin;
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;
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);
}
}
}這個(gè)方法比較固定，大家可以網(wǎng)上自行下載。在MainActivity中添加一條語(yǔ)句即可添加橫線：
public class MainActivity extends Activity {
private RecyclerView mRecyclerView;
private List<String> mDatas;
private MyAdapter myAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
mRecyclerView = (RecyclerView) findViewById(R.id.recycleview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mRecyclerView.setAdapter(myAdapter = new MyAdapter(this,mDatas));
mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));
}
protected void initData() {
mDatas = new ArrayList<String>();
for (int i = 1; i < 20; i++) {
mDatas.add("" + i);
}
}
}調(diào)用了RecyclerView的addItemDecoration方法，傳入DividerItemDecoration對(duì)象，實(shí)例化該對(duì)象時(shí)傳入了兩個(gè)參數(shù)，一個(gè)是上下文對(duì)象，一個(gè)是排列布局方式。 運(yùn)行項(xiàng)目實(shí)例如下：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-5.png" alt="這里寫(xiě)圖片描述" />
這時(shí)可以看到每個(gè)Item之間有了一條淺淺灰色分割線。這個(gè)灰色的分割線不夠明顯，也不美觀，我們可以借助主題的listDivider屬性改變分割線，找到當(dāng)前主題，添加一條語(yǔ)句如下（加粗語(yǔ)句）：
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">@color/colorPrimary</item>
<item name="colorPrimaryDark">@color/colorPrimaryDark</item>
<item name="colorAccent">@color/colorAccent</item>
<item name="android:listDivider">@drawable/bg</item>
</style>
</resources>再次運(yùn)行項(xiàng)目實(shí)例如下：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-6.png" alt="這里寫(xiě)圖片描述" />
分割線變成了我們自定義個(gè)bg圖片，這時(shí)就可以實(shí)現(xiàn)任意的自定義了。 上面實(shí)現(xiàn)了類(lèi)似ListView的布局方式，下面實(shí)現(xiàn)一個(gè)類(lèi)似GridView的布局方式，這里需要修改一下MainActivity的一條語(yǔ)句（加粗），如下：
public class MainActivity extends Activity {
private RecyclerView mRecyclerView;
private List<String> mDatas;
private MyAdapter myAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
mRecyclerView = (RecyclerView) findViewById(R.id.recycleview);
mRecyclerView.setLayoutManager(new GridLayoutManager(this,4));
mRecyclerView.setAdapter(myAdapter = new MyAdapter(this, mDatas));
mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));
}
protected void initData() {
mDatas = new ArrayList<String>();
for (int i = 1; i < 20; i++) {
mDatas.add("" + i);
}
}
}setLayoutManager方法傳入了GridLayoutManager的對(duì)象，實(shí)例化該對(duì)象需要兩個(gè)參數(shù)，第一個(gè)是上下文對(duì)象，第二個(gè)是每一行顯示item的個(gè)數(shù)。
運(yùn)行實(shí)例如下：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-7.png" alt="這里寫(xiě)圖片描述" />
可以看到類(lèi)似GridView的效果，但是分割線好像不太正確，我們還需要新建一個(gè)分割線類(lèi)：
public class DividerGridItemDecoration extends RecyclerView.ItemDecoration {
private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
private Drawable mDivider;
public DividerGridItemDecoration(Context context) {
final TypedArray a = context.obtainStyledAttributes(ATTRS);
mDivider = a.getDrawable(0);
a.recycle();
}
@Override
public void onDraw(Canvas c, RecyclerView parent, State state) {
drawHorizontal(c, parent);
drawVertical(c, parent);
}
private int getSpanCount(RecyclerView parent) {
// 列數(shù)
int spanCount = -1;
LayoutManager layoutManager = parent.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
spanCount = ((StaggeredGridLayoutManager) layoutManager)
.getSpanCount();
}
return spanCount;
}
public void drawHorizontal(Canvas c, RecyclerView parent) {
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.getLeft() - params.leftMargin;
final int right = child.getRight() + params.rightMargin
+ mDivider.getIntrinsicWidth();
final int top = child.getBottom() + params.bottomMargin;
final int bottom = top + mDivider.getIntrinsicHeight();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
public void drawVertical(Canvas c, RecyclerView parent) {
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.getTop() - params.topMargin;
final int bottom = child.getBottom() + params.bottomMargin;
final int left = child.getRight() + params.rightMargin;
final int right = left + mDivider.getIntrinsicWidth();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
private boolean isLastColum(RecyclerView parent, int pos, int spanCount,
int childCount) {
LayoutManager layoutManager = parent.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
if ((pos + 1) % spanCount == 0)// 如果是最后一列，則不需要繪制右邊
{
return true;
}
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
int orientation = ((StaggeredGridLayoutManager) layoutManager)
.getOrientation();
if (orientation == StaggeredGridLayoutManager.VERTICAL) {
if ((pos + 1) % spanCount == 0)// 如果是最后一列，則不需要繪制右邊
{
return true;
}
} else {
childCount = childCount - childCount % spanCount;
if (pos >= childCount)// 如果是最后一列，則不需要繪制右邊
return true;
}
}
return false;
}
private boolean isLastRaw(RecyclerView parent, int pos, int spanCount,
int childCount) {
LayoutManager layoutManager = parent.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
childCount = childCount - childCount % spanCount;
if (pos >= childCount)// 如果是最后一行，則不需要繪制底部
return true;
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
int orientation = ((StaggeredGridLayoutManager) layoutManager)
.getOrientation();
// StaggeredGridLayoutManager 且縱向滾動(dòng)
if (orientation == StaggeredGridLayoutManager.VERTICAL) {
childCount = childCount - childCount % spanCount;
// 如果是最后一行，則不需要繪制底部
if (pos >= childCount)
return true;
} else
// StaggeredGridLayoutManager 且橫向滾動(dòng)
{
// 如果是最后一行，則不需要繪制底部
if ((pos + 1) % spanCount == 0) {
return true;
}
}
}
return false;
}
@Override
public void getItemOffsets(Rect outRect, int itemPosition,
RecyclerView parent) {
int spanCount = getSpanCount(parent);
int childCount = parent.getAdapter().getItemCount();
if (isLastRaw(parent, itemPosition, spanCount, childCount))// 如果是最后一行，則不需要繪制底部
{
outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
} else if (isLastColum(parent, itemPosition, spanCount, childCount))// 如果是最后一列，則不需要繪制右邊
{
outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
} else {
outRect.set(0, 0, mDivider.getIntrinsicWidth(),
mDivider.getIntrinsicHeight());
}
}
}getItemOffsets方法中進(jìn)行了邏輯判斷，最后一行時(shí)，不必繪制底部分割線，最后一列，不必繪制右邊的分割線。將主題中的自定義分割線語(yǔ)句去除，再次運(yùn)行項(xiàng)目：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-8.png" alt="這里寫(xiě)圖片描述" />
下面講解第三種布局方式-瀑布流的實(shí)現(xiàn)，首先我們修改MainActivity代碼如下：
public class MainActivity extends Activity {
private RecyclerView mRecyclerView;
private List<String> mDatas;
private MyAdapter myAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
mRecyclerView = (RecyclerView) findViewById(R.id.recycleview);
mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,StaggeredGridLayoutManager.VERTICAL));
// mRecyclerView.setLayoutManager(new GridLayoutManager(this, 4));
mRecyclerView.setAdapter(myAdapter = new MyAdapter(this, mDatas));
//mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));
mRecyclerView.addItemDecoration(new DividerGridItemDecoration(this));
}
protected void initData() {
mDatas = new ArrayList<String>();
for (int i = 1; i < 100; i++) {
mDatas.add("" + i);
}
}
}修改部分加粗，在setLayoutManager方法中傳入了StaggeredGridLayoutManager的對(duì)象，對(duì)象初始化傳入兩個(gè)參數(shù)，第一個(gè)是每一行的列數(shù)，第二個(gè)是布局方式。 此外，我們還需要修改適配器文件，隨機(jī)化子控件的高度，這樣才有瀑布流的效果，如下：
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
private Context context;
private List<String> datas;
private List<Integer> mHights;
public MyAdapter(Context context,List<String> datas){
this.context=context;
this.datas=datas;
mHights=new ArrayList<>();
for (int i=0;i<datas.size();i++){
mHights.add((int)(50+Math.random()*300));
}
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
MyViewHolder holder = new MyViewHolder(LayoutInflater.from(
context).inflate(R.layout.item, parent,
false));
return holder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
ViewGroup.LayoutParams layoutparams= holder.itemView.getLayoutParams();
layoutparams.height=mHights.get(position);
holder.itemView.setLayoutParams(layoutparams);
holder.tv.setText(datas.get(position));
}
@Override
public int getItemCount() {
return datas.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView tv;
public MyViewHolder(View view) {
super(view);
tv = (TextView) view.findViewById(R.id.id_num);
}
}
}新添加了一個(gè)List對(duì)象mHeights用于存儲(chǔ)隨機(jī)的高度數(shù)值，在onBindViewHolder方法中為T(mén)extView控件設(shè)置了隨機(jī)的高度。 運(yùn)行實(shí)例如下：
http://wiki.jikexueyuan.com/project/twenty-four-Scriptures/images/23-9.png" alt="這里寫(xiě)圖片描述" />
可以看出，所有的子Item的高度都是隨機(jī)產(chǎn)生的，也就產(chǎn)生了瀑布流的效果，我們可以看出，RecyclerView較傳統(tǒng)的控件來(lái)講使用更為靈活，在今后的開(kāi)發(fā)中也將會(huì)經(jīng)常用到。
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