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recyclerview是android 5.0新增的控件，在android-support-v7下面。官方文档对recycleview介绍很简洁到位，如下：
a flexible view for providing a limited window into a large data set.
大概意思就是说：在有限大小的窗口里显示大量数据的一个灵活的view。
下面是reccleview继承图：
看到这里我们自然想到了与之类似的控件listview，recyclerview和listview都是在有限的屏幕区域里维护少量的view来进行显示大量的数据，其实recyclerview是listview的升级版，功能更加强大，更加灵活，扩展性更强，google建议使用recycleview替代listview。
下面是recycleview结构图：
recycleview主要包括以下几个部件：
1. recyclerview.adapter
数据和视图的分离设计是程序解耦和可维护的重要指标，recycleview作为展示大量数据的view肯定是遵循这个设计的，listview也不例外。通过继承recycleview.adapter即可轻松实现自己的adapter，主要重写recycleview.adapter的下面三个方法即可实现：
public myrecycleviewadapter.myviewholder oncreateviewholder(viewgroup parent, int viewtype) public void onbindviewholder(myrecycleviewadapter.myviewholder holder, int position) public int getitemcount()
上面myrecycleviewadapter是我自己定义的viewholder
2. viewholder
viewholder用来保存列表中item view引用的类，这样做的目的是重用item视图，从而提高性能。
在listview中，viewholder不是listview自带的，是需要自己定义的，当然你也可以不使用viewholder，这样的后果就是listview每次调用getview()方法的时候都会调用findviewbyid()方法，要知道findviewbyid()性能很差，它通过递归的方式去从view树中找特定的子view的，最终往往带来很差的性能体验，所以使用viewholder也成了优化listview最重要的手段。
在recyclerview中，android内置了recyclerview.viewholder，这意味着viewholder使用成了必须。
3. 分割线 recycleview.itemdecoration
listview添加分割线很简单，只需在listview的xml中配置”divider”属性即可，如：
android:dividerheight="2dp" android:divider="@color/red"
但recycleview添加分割线是比较麻烦的，并且默认是不带分割线的。但实际开发中一般都需要分割线，使用recycleview.itemdecoration为recycleview添加分割线
4. 布局管理器 layoutmanager
recycleview支持多种布局模式：
1、linearlayoutmanager
线性布局管理器，支持水平布局和垂直布局两种
2、gridlayoutmanager
网格布局管理器
3、staggerdgridlayoutmanager
错列的网格布局管理器，可以实现瀑布流列表
recycleview使用时和listview很类似，直接看一个简单的例子，分别展示一个垂直方向和水平方向上的列表，并且都支持使用颜色和图片做分割线，效果图如下：
1. mainactivity
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package com.cjl.recycleviewtest;
...
public class mainactivity extends appcompatactivity {
private verticalfragment mverticalfragment;
private horizontalfragment mhorizontalfragment;
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
//垂直
mverticalfragment = new verticalfragment();
//水平
mhorizontalfragment = new horizontalfragment();
//默认为设置垂直
getfragmentmanager().begintransaction().replace(r.id.activity_main, mverticalfragment).commit();
}
@override
public boolean oncreateoptionsmenu(menu menu) {
menuinflater inflater = getmenuinflater();
inflater.inflate(r.menu.menu_recycleview, menu);
return super.oncreateoptionsmenu(menu);
}
@override
public boolean onoptionsitemselected(menuitem item) {
int id = item.getitemid();
switch (id) {
//垂直方向
case r.id.vertical:
verticalfragment mverticalfragment = new verticalfragment();
getfragmentmanager().begintransaction().replace(r.id.activity_main, mverticalfragment).commit();
break;
//水平方向
case r.id.horizontal:
getfragmentmanager().begintransaction().replace(r.id.activity_main, mhorizontalfragment).commit();
break;
}
return super.onoptionsitemselected(item);
}
}
mainactivity布局文件 r.layout.activity_main
<?xml version="1.0" encoding="utf-8"?> <framelayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent"> </framelayout>
2. 垂直方向上 verticalfragment
public class verticalfragment extends fragment implements view.onclicklistener{
private recyclerview mrecycleviewdrawable;
private recyclerview mrecycleviewcolor;
private linearlayoutmanager mmanagercolor;
private linearlayoutmanager mmanagerdrawable;
private list<string> mdata;
private button mdrawable;
private button mcolor;
private myrecycleviewadapter mrecycleviewadapter;
@nullable
@override
public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate) {
view view = inflater.inflate(r.layout.fragment_vertical_layout, container, false);
mrecycleviewdrawable = (recyclerview) view.findviewbyid(r.id.recycleview_drawable);
mrecycleviewcolor = (recyclerview) view.findviewbyid(r.id.recycleview_color);
mdrawable = (button) view.findviewbyid(r.id.btn_drawable);
mdrawable.setonclicklistener(this);
mcolor = (button) view.findviewbyid(r.id.btn_color);
mcolor.setonclicklistener(this);
//1. 颜色分割线
mmanagercolor = new linearlayoutmanager(getactivity());
mmanagercolor.setorientation(linearlayoutmanager.vertical);
mrecycleviewcolor.setlayoutmanager(mmanagercolor);
//设置颜色分割线
mrecycleviewcolor.additemdecoration(new lineardivider(getactivity(), linearlayoutmanager.vertical, 10, this.getresources().getcolor(r.color.coloraccent)));
//2. 图片分割线
mmanagerdrawable = new linearlayoutmanager(getactivity());
mmanagerdrawable.setorientation(linearlayoutmanager.vertical);
mrecycleviewdrawable.setlayoutmanager(mmanagerdrawable);
//设置图片分割线
drawable drawable = contextcompat.getdrawable(getactivity(), r.mipmap.divider);
mrecycleviewdrawable.additemdecoration(new lineardivider(getactivity(), linearlayoutmanager.vertical, 20, drawable));
mdata = new arraylist<string>();
initdata(mdata);
//自定义adapter
mrecycleviewadapter = new myrecycleviewadapter(getactivity(), r.layout.item_vertical_recycleview, mdata);
//设置adapter
mrecycleviewcolor.setadapter(mrecycleviewadapter);
mrecycleviewdrawable.setadapter(mrecycleviewadapter);
return view;
}
private void initdata(list<string> datalist) {
for (int i = 0; i < 30; i++) {
datalist.add("item" + i);
}
}
@override
public void onclick(view view) {
int id = view.getid();
switch (id){
case r.id.btn_drawable:
mrecycleviewcolor.setvisibility(view.invisible);
mrecycleviewdrawable.setvisibility(view.visible);
break;
case r.id.btn_color:
mrecycleviewcolor.setvisibility(view.visible);
mrecycleviewdrawable.setvisibility(view.invisible);
break;
}
}
}
verticalfragment 的布局文件 r.layout.fragment_vertical_layout
<?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_drawable" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginbottom="60dp"/> <android.support.v7.widget.recyclerview android:id="@+id/recycleview_color" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginbottom="60dp" android:visibility="invisible"/> <linearlayout android:id="@+id/lilayout" android:orientation="horizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:weightsum="2" android:layout_alignparentbottom="true"> <button android:id="@+id/btn_drawable" android:layout_width="wrap_content" android:layout_height="50dp" android:text="图片分割线" android:gravity="center" android:layout_weight="1" android:background="@color/colorprimary"/> <button android:id="@+id/btn_color" android:layout_width="wrap_content" android:layout_height="50dp" android:text="颜色分割线" android:gravity="center" android:layout_weight="1" android:background="@color/mytv"/> </linearlayout> </relativelayout>
3. 直接继承recyclerview.adapter
public class myrecycleviewadapter extends recyclerview.adapter<myrecycleviewadapter.myviewholder> {
private layoutinflater mlayoutinflater;
private list<string> mdatalist;
private int mitemlayout;
public myrecycleviewadapter(context context, int itemlayout, list<string> datalist) {
mlayoutinflater = layoutinflater.from(context);
mitemlayout = itemlayout;
mdatalist = datalist;
}
@override
public myrecycleviewadapter.myviewholder oncreateviewholder(viewgroup parent, int viewtype) {
return new myviewholder(mlayoutinflater.inflate(mitemlayout, parent, false));
}
@override
public void onbindviewholder(myrecycleviewadapter.myviewholder holder, int position) {
holder.mtextview.settext(mdatalist.get(position));
}
@override
public int getitemcount() {
return mdatalist.size();
}
class myviewholder extends recyclerview.viewholder {
private textview mtextview;
public myviewholder(view itemview) {
super(itemview);
mtextview = (textview) itemview.findviewbyid(r.id.tv);
}
}
}
item布局文件 item_vertical_recycleview.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="wrap_content"> <textview android:id="@+id/tv" android:gravity="center" android:layout_width="match_parent" android:layout_height="60dp"/> </framelayout>
4. 分割线 recyclerview.itemdecoration
public class lineardivider extends recyclerview.itemdecoration {
private drawable mdividerdarwable;
private int morientation;
private int mdividerhight = 1;
private paint mcolorpaint;
public final int[] atrrs = new int[]{
android.r.attr.listdivider
};
/*
orientation 方向
*/
public lineardivider(context context, int orientation) {
final typedarray ta = context.obtainstyledattributes(atrrs);
this.mdividerdarwable = ta.getdrawable(0);
ta.recycle();
setorientation(orientation);
}
/*
int orientation 方向
int dividerhight 分割线的线宽
drawable dividerdrawable 充当分割线的图片
*/
public lineardivider(context context, int orientation, int dividerhight, drawable dividerdrawable) {
this(context, orientation);
mdividerhight = dividerhight;
mdividerdarwable = dividerdrawable;
}
/*
int orientation 方向
int dividerhight 分割线的线宽
int dividercolor 分割线的颜色
*/
public lineardivider(context context, int orientation, int dividerhight, int dividercolor) {
this(context, orientation);
mdividerhight = dividerhight;
mcolorpaint = new paint();
mcolorpaint.setcolor(dividercolor);
}
public void setorientation(int orientation) {
if (orientation != linearlayoutmanager.horizontal && orientation != linearlayoutmanager.vertical) {
throw new illegalargumentexception("方向参数错误！");
}
morientation = orientation;
}
@override
public void ondraw(canvas c, recyclerview parent, recyclerview.state state) {
super.ondraw(c, parent, state);
if (morientation == linearlayoutmanager.horizontal) {
drawhorizontaldivider(c, parent);
} else {
drawvirticaldivider(c, parent);
}
}
//画垂直分割线
public void drawvirticaldivider(canvas c, recyclerview parent) {
int left = parent.getpaddingleft();
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;
final int bottom = top + mdividerhight;
if (mdividerdarwable != null) {
mdividerdarwable.setbounds(left, top, right, bottom);
mdividerdarwable.draw(c);
}
if (mcolorpaint != null) {
c.drawrect(left, top, right, bottom, mcolorpaint);
}
}
}
//画水平分割线
public void drawhorizontaldivider(canvas c, recyclerview parent) {
int top = parent.getpaddingtop();
int bottom = parent.getheight() - parent.getpaddingbottom();
final int childcount = parent.getchildcount();
for (int i = 0; i < childcount; i++) {
final view child = parent.getchildat(i);
recyclerview.layoutparams params = (recyclerview.layoutparams) child.getlayoutparams();
final int left = child.getright() + params.rightmargin;
final int right = left + mdividerhight;
if (mdividerdarwable != null) {
mdividerdarwable.setbounds(left, top, right, bottom);
mdividerdarwable.draw(c);
}
if (mcolorpaint != null) {
c.drawrect(left, top, right, bottom, mcolorpaint);
}
}
}
@override
public void getitemoffsets(rect outrect, view view, recyclerview parent, recyclerview.state state) {
super.getitemoffsets(outrect, view, parent, state);
if (morientation == linearlayoutmanager.horizontal) {
outrect.set(0, 0, 0, mdividerhight);
} else {
outrect.set(0, 0, mdividerhight, 0);
}
}
}
未完待续……
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