Android开发菜鸟——RecyclerView

RecyclerView整合了ListView和GridView两者的特性，即可以用RecyclerView替换这两者。

一、使用方法

1、布局使用RecyclerView

            
itemCount、listitem只是为了预览而设置的，不是必须的。

2、设置列表格式layoutManager

网格列表
recyclerView.layoutManager = GridLayoutManager(this, 3)

线性列表
recyclerView.layoutManager = LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false)

瀑布列表
recyclerView.layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)

3、设置适配器adapter

recyclerView.adapter = RecycleAdapter()

二、通用Adapter

abstract class RecycleAdapter(private var mDataSet: ArrayList, private var listener: IRecyclerViewListener?): RecyclerView.Adapter() {
	// 按layoutResId保存holder
    private var mHolders: SparseArray = SparseArray()

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecycleViewHolder {
        var mHolder = getHolder(viewType)
        if (mHolder == null) {
        	// 创建holder
            mHolder = RecycleViewHolder.get(parent, getLayoutId(viewType))
            putHolder(viewType, mHolder)
        }
        return mHolder
    }

    override fun getItemCount(): Int {
        return mDataSet.size
    }

	// 可以在此给列表项设置宽高
    override fun onBindViewHolder(holder: RecycleViewHolder, position: Int) {
        holder.itemView.setOnClickListener {
            listener?.onItemClickListener(position)
        }
        holder.itemView.setOnLongClickListener {
            listener?.onItemLongClickListener(position)
            true
        }
        convert(holder, mDataSet[position], position)
    }
    
    private fun getHolder(viewType: Int): RecycleViewHolder? {
        return mHolders.get(viewType)
    }
    
    private fun putHolder(viewType: Int, holder: RecycleViewHolder) {
        mHolders.put(viewType, holder)
    }
    
    abstract fun getLayoutId(viewType: Int): Int
    
    // 也可以在此给列表项设置宽高
    abstract fun convert(holder: RecycleViewHolder, data: T, position: Int)
}

三、常用配置

1、设置间隔

线性列表的间隔比较容易就不说了。

可添加多个间隔设置
recyclerView.addItemDecoration()

官方提供有DividerItemDecoration
recyclerView.addItemDecoration(DividerItemDecoration(context, orientation))

间隔实现类：可组合实现多种效果
class MyItemDecoration : RecyclerView.ItemDecoration() {
    /**
     * 设置padding：即设置Rect的left、top、right、bottom
     */
    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
       super.getItemOffsets(outRect, view, parent, state)
    }
    /**
     * 绘制背景
     * canvas可以绘制各种图形文字
     */
    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        super.onDraw(c, parent, state)
    }
    /**
     * 绘制遮罩
     * canvas可以绘制各种图形文字
     */
    override fun onDrawOver(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        super.onDrawOver(c, parent, state)
    }
}

2、设置网格列表项宽度不同占比

/**
 * A {@link RecyclerView.LayoutManager} implementations that lays out items in a grid.
 * 

 * By default, each item occupies 1 span. You can change it by providing a custom
 * {@link SpanSizeLookup} instance via {@link #setSpanSizeLookup(SpanSizeLookup)}.
 */
public class GridLayoutManager extends LinearLayoutManager {}

通过官方代码注释可以看到，想要设置列表项占比，可以通过setSpanSizeLookup实现。以下是默认的SpanSizeLookup，可以看到列表项占比都是1，所以只需要覆写getSpanSize就行了

/**
     * Default implementation for {@link SpanSizeLookup}. Each item occupies 1 span.
     */
    public static final class DefaultSpanSizeLookup extends SpanSizeLookup {

        @Override
        public int getSpanSize(int position) {
            return 1;
        }

        @Override
        public int getSpanIndex(int position, int spanCount) {
            return position % spanCount;
        }
    }

四、自定义

RecycleView目前支持三种LayoutManager，如果这三种LayoutManager不能满足UI设计效果，可以通过自定义LayoutManager进行修改。