xamarin学习笔记A05(安卓RecycleView简单显示)

每次学习一点xamarin就写个博客和做个学习笔记视频来加深记忆巩固知识)
如有不正确的地方，请帮我指正。

首先从Nuget下载好下面两个包
Xamarin.Android.Support.v7.AppCompat
Xamarin.Android.Support.v7.RecyclerView

RecyclerView里的主要类说明

RecyclerView.Adapter 创建每个Item
RecyclerView.LayoutManager 设置Item的布局形式
RecyclerView.ItemDecoration 设置Item装饰效果
RecyclerView.ViewHolder 用于缓存Item
RecyclerView.ItemAnimator 设置Item的动画效果

实现一个简单的书本列表功能

一.新建布局文件Book.axml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:minWidth="25px"    android:minHeight="25px">    <android.support.v7.widget.RecyclerView        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/recyclerView1" /></LinearLayout>

二.新建布局文件BookItem.axml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="horizontal"    android:layout_width="match_parent"    android:layout_height="wrap_content">    <ImageView        android:id="@+id/image_book"        android:layout_width="wrap_content"        android:layout_height="wrap_content"         android:layout_marginLeft="20dp"/>    <TextView        android:textSize="24sp"        android:id="@+id/text_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_vertical" /></LinearLayout>

三.新建一个Book类

public class Book    {        private string name; //书名        private int imageId; //图片Id        public string Name { get => name; set => name = value; }        public int ImageId { get => imageId; set => imageId = value; }        public Book(string name, int imageId)        {            Name = name;            ImageId = imageId;        }}

四.新建BookAdapter类

public class BookAdapter : RecyclerView.Adapter    {        private List<Book> m_BookList;        public BookAdapter(List<Book> bookList)        {            m_BookList = bookList;        }        public override int ItemCount        {            get { return m_BookList.Count; }        }        //一个Item的数据绑定事件        public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)        {            Book book = m_BookList[position];            BookViewHolder bookHolder = holder as BookViewHolder;            bookHolder.Book = book;            bookHolder.BookImage.SetImageResource(book.ImageId);            bookHolder.NameText.Text = book.Name;            bookHolder.BookImage.Tag = position; //保存position到Tag里        }        //一个Item的初始化事件        public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)        {            View view = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.BookItem, parent, false);            BookViewHolder holder = new BookViewHolder(view);            return holder;        }        public override void OnViewRecycled(Java.Lang.Object holder)        {            base.OnViewRecycled(holder);            BookViewHolder bookHolder = holder as BookViewHolder;        }        protected class BookViewHolder:RecyclerView.ViewHolder        {            public ImageView BookImage;            public TextView NameText;            public Book Book;            public BookViewHolder(View view):base(view)            {                BookImage = view.FindViewById(Resource.Id.image_book) as ImageView;                NameText = view.FindViewById(Resource.Id.text_name) as TextView;            }        }}

五.新建BookActivity

public class BookActivity : AppCompatActivity    {        private List<Book> m_BookList = new List<Book>();        protected override void OnCreate(Bundle savedInstanceState)        {            base.OnCreate(savedInstanceState);            SetContentView(Resource.Layout.Book);            InitBooks(); //初始化数据            RecyclerView recyclerView = this.FindViewById(Resource.Id.recyclerView1) as RecyclerView;            LinearLayoutManager layoutManager = new LinearLayoutManager(this);            BookAdapter adapter = new BookAdapter(m_BookList);            recyclerView.SetLayoutManager(layoutManager);   //给recyclerView设置布局管理器对象            recyclerView.SetAdapter(adapter);   //给recyclerView设置适配器对象            recyclerView.AddItemDecoration(new BookItemDecoration(this)); //给recyclerView设置装饰对象        }        private void InitBooks()        {            int count = 0;            Book book = null;            for (int i = 0; i <= 2; i++) //初始化15本书的数据            {                book = new Book("Book" + count.ToString("000"), Resource.Drawable.a1);                m_BookList.Add(book);                count++;                book = new Book("Book" + count.ToString("000"), Resource.Drawable.a2);                m_BookList.Add(book);                count++;                book = new Book("Book" + count.ToString("000"), Resource.Drawable.a3);                m_BookList.Add(book);                count++;                book = new Book("Book" + count.ToString("000"), Resource.Drawable.a4);                m_BookList.Add(book);                count++;                book = new Book("Book" + count.ToString("000"), Resource.Drawable.a5);                m_BookList.Add(book);                count++;            }        }    }

六.添加分割线

/// <summary>    /// RecyclerView的Item的装饰对象(扩展自RecyclerView.ItemDecoration)    /// </summary>    public class BookItemDecoration : RecyclerView.ItemDecoration    {        private Paint m_Paint;        private float m_SplitLine; //分割线厚度        private Bitmap m_BitMap;        public BookItemDecoration(Context context)        {            m_Paint = new Paint();            m_Paint.AntiAlias = true;//设置抗锯齿            m_Paint.Color = Color.Blue;            m_BitMap = BitmapFactory.DecodeResource(context.Resources, Resource.Drawable.Mark);        }        public override void GetItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state)        {            base.GetItemOffsets(outRect, view, parent, state);            if (parent.GetChildAdapterPosition(view) == 0)//第一个BookItem不需要设置top值            {                outRect.Top = 0;            }            else            {                outRect.Top = 2;                m_SplitLine = 2; //将分隔线的厚度保存到m_OutRectTop变量中以供OnDraw中使用            }        }        public override void OnDraw(Canvas c, RecyclerView parent, RecyclerView.State state)        {            base.OnDraw(c, parent, state);            int itemCount = parent.ChildCount;            for (int i = 0; i < itemCount; i++)            {                View view = parent.GetChildAt(i);                int position = parent.GetChildAdapterPosition(view);                if (position == 0) //第一个BookItemView不要绘制                    continue;                float outRectTop = view.Top - m_SplitLine;                float outRectLeft = parent.PaddingLeft;                float outRectBottom = view.Top;                float outRectRight = parent.Width - parent.PaddingRight;                if(i%2==0) //偶数行画蓝色线                    m_Paint.Color = Color.Blue;                else                    m_Paint.Color = Color.Red;                c.DrawRect(outRectLeft, outRectTop, outRectRight, outRectBottom, m_Paint);            }        }        public override void OnDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state)        {            base.OnDrawOver(c, parent, state);            int itemCount = parent.ChildCount;            for (int i = 0; i < itemCount; i++)            {                View view = parent.GetChildAt(i);                int position = parent.GetChildAdapterPosition(view);                if (position < 3) //把前三本书的图片上覆盖上"包邮"的图片                    c.DrawBitmap(m_BitMap, 1, view.Top, m_Paint);            }        }    }

分割线的原理
是利用RecyclerView.ItemDecoration 装饰类来实现的。
通过给每一个ItemView的外面画一个OutRect，利用OutRect与ItemView的空隙用上背景色来做模拟分割线或者其它东西。

这个例子中只设置了outRect.Top=2，所以OutRect与ItemView的上面空隙为2px，实现了厚度为2px的分割线。利用Paint类在OnDraw方法来设置OutRect的背景色。

视频和完整代码上传到了CSDN的资源中http://download.csdn.net/download/junshangshui/9865033