我们做Android开发，当需要大量加载图片时，一般会用到ListView、GridView等，那么RecyclerView这样的控件又能做什么用呢，为什么要用RecyclerView呢？
RecyclerView is a more advanced and flexible version of ListView. This widget is a Container for large sets of views that can be recycled and scrolled very efficiently. Use the RecyclerView widget when you have lists with elements that change dynamically.
简单说，它是ListView的进化，为了当你需要动态展示一组数据的时候就会需要它。
RecyclerView的整体使用思路如下：
你想要控制其显示的方式，请通过布局管理器LayoutManager
你想要控制Item间的间隔（可绘制），请通过ItemDecoration
-
你想要控制Item增删的动画，请通过ItemAnimator
通过以上三步设置，可以让RecyclerView显示出各种神奇的效果出来。RecyclerView使用过程如下：
1.RecyclerView是support-v7包中的新组件，使用之前需要导入support-v7。
2.activity_main.xml的布局如下,在布局文件里引用RecyclerView控件
<span style="font-family:SimHei;font-size:14px;"><?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"
tools:context="com.example.ahuang.recyclerview.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>
</RelativeLayout>
</span> ```
###### 3.每个Item的布局如下,很简单，只有一个TextView
<span style="font-family:SimHei;font-size:14px;"><?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="vertical">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>
</LinearLayout>
</span> ```
4. RecyclerView的适配器
- RecyclerView的适配器继承自RecyclerView.Adapter
- 重写内部类RecyclerView.ViewHolder
- 实现onCreateViewHolder（），onBindViewHolder（）和getItemCount()三个方法。
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder>{
Context context;
List<String> list;
public MyAdapter(Context context,List<String> list){
this.context=context;
this.list=list;
}
@Override
public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
MyViewHolder holder=new MyViewHolder(LayoutInflater.from(context).inflate(R.layout.lv_item_layout,parent,false));
return holder;
}
@Override
public void onBindViewHolder(MyAdapter.MyViewHolder holder, int position) {
holder.tv.setText(list.get(position));
}
@Override
public int getItemCount() {
return list.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder{
TextView tv;
public MyViewHolder(View itemView) {
super(itemView);
tv=(TextView) itemView.findViewById(R.id.textView);
}
}
}
</span> ```
###### 5.主Activity中实现
只需上文提到的关键三步即可实现。
public class MainActivity extends ActionBarActivity {
private RecyclerView mRecyclerView;
private List<String> list;
private MyAdapter myAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
init();
mRecyclerView=(RecyclerView) findViewById(R.id.recyclerView);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mRecyclerView.setAdapter(new MyAdapter(this,list));
}
private void init(){
list=new ArrayList<String>();
for(int i='A';i<'z';i++){
list.add(""+(char)i);
}
}
} ```
效果如下
但是，可以看到RecyclerView是没有分隔线的，而且RecyclerView并没有支持divider这样的属性，那应该怎样添加分割线呢，下面就用到了ItemDecoration，我们可以通过该方法添加分割线mRecyclerView.addItemDecoration()，通过它，我们可以随意地添加我们自定义的分割线。
当我们调用mRecyclerView.addItemDecoration()方法添加decoration的时候，RecyclerView在绘制的时候，去会绘制decorator，即调用该类的onDraw和onDrawOver方法，该类参考自：[DividerItemDecoration(http://blog.csdn.net/lmj623565791/article/details/38173061)，代码如下
- onDraw方法先于drawChildren
- onDrawOver在drawChildren之后，一般我们选择复写其中一个即可。
- getItemOffsets 可以通过outRect.set()为每个Item设置一定的偏移量，主要用于绘制Decorator。
/**
* Created by ahuang on 2016/1/8.
*/
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) {
super.onDraw(c, 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);
android.support.v7.widget.RecyclerView v = new android.support.v7.widget.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) {
super.getItemOffsets(outRect, itemPosition, parent);
if (mOrientation == VERTICAL_LIST) {
outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
} else {
outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
}
}
} ```
前面说了，我们可以随意添加我们自定义的分割线，具体步骤如下：首先要自定义分割线，在drawable下画一个分割线的shape.
在这个shape里，你可以自定义分割线的形状。
<pre name="code" class="java"><?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<solid android:color="#FFC125"></solid>
<size android:height="2dp"></size>
</shape> ```
接下来就是要将自定义的shape应用到RecyclerView中。
<pre name="code" class="java"><resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="android:listDivider">@drawable/divider_bg</item>
</style>
</resources> ```
效果图如此下：
