Kotlin编写RecyclerView的Adapter

kotlin在现在的Android开发中已经较为常见，空闲之余学习一下还是非常必要的，没准儿哪天就可以利用它进行些骚操作呢（梦想还是要有的）。

利用Kotlin编写一个简单的Adapter

class SimpleAdapter(private val context: Context, private val data: List<String>) : RecyclerView.Adapter<SimpleAdapter.SimpleViewHolder>() {
    override fun onBindViewHolder(holder: SimpleViewHolder?, position: Int) {
        holder?.textView?.text = data[position]
    }

    override fun getItemCount(): Int = data.size

    override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): SimpleViewHolder
            = SimpleViewHolder(LayoutInflater.from(context)
            .inflate(R.layout.item_recycler, parent, false))

    inner class SimpleViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        var textView: TextView = view.findViewById(R.id.item_tv)
    }
}
           

上面adapter完成了一个List集合数据的简单绑定，是不是发现相对于用Java实现同样功能代码更为精简。

在onBindViewHolder方法里面调用如下代码

holder?.textView?.setOnClickListener {
            Toast.makeText(context, "click", Toast.LENGTH_SHORT).show()
        }
           

为item中的控件设置监听器，至此一个简单的adapter编写完成。

Adapter中包含不同item类型

废话不多说直接上代码

class RecyclerAdapter(private val context: Context, private val data: List<String>)
    : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    private val HEADER = 
    private val NORMAL = 
    private val FOOTER = 

    override fun getItemCount(): Int = data.size


    override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder? = when (viewType) {
        HEADER -> {
            HeaderViewHolder(LayoutInflater.from(context).
                    inflate(R.layout.item_header, parent, false))
        }

        FOOTER -> {
            FooterViewHolder(LayoutInflater.from(context)
                    .inflate(R.layout.item_footer, parent, false))
        }

        else -> {
            RecyclerViewHolder(LayoutInflater.from(context)
                    .inflate(R.layout.item_recycler, parent, false))
        }

    }

    /**
     * 利用kotlin中的when代替Java中的if/else
     * 返回不同的item类型
     */
    override fun getItemViewType(position: Int): Int = when (position) {
         -> {
            HEADER
        }
        itemCount -  -> {
            FOOTER
        }
        else -> {
            NORMAL
        }
    }

    /**
     * 根据不同的item类型绑定不同的数据
     */
    override fun onBindViewHolder(holder: RecyclerView.ViewHolder?, position: Int) {
        when (getItemViewType(position)) {
            HEADER -> {
                if (holder is HeaderViewHolder) {
                    holder.tv.text = "I am Header"
                    holder.tv.setOnClickListener {
                        Toast.makeText(context, "I am Header", Toast.LENGTH_SHORT).show()
                    }
                }
            }
            FOOTER -> {
                if (holder is FooterViewHolder) {
                    holder.tv.text = "I am Footer"
                }
            }
            else -> {
                if (holder is RecyclerViewHolder) {
                    holder?.textView?.text = data[position]
                    holder.textView.setOnClickListener {
                        Toast.makeText(context, "click", Toast.LENGTH_SHORT).show()
                    }
                }
            }
        }
    }

    inner class RecyclerViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        var textView: TextView = view.findViewById(R.id.item_tv)
    }

    class HeaderViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        var tv: TextView = view.findViewById(R.id.tv_header)
    }

    inner class FooterViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        var tv: TextView = view.findViewById(R.id.tv_footer)
    }
}
           

全文字随便来张效果图吧

如果某个item中控件的监听器我不想写在或者不能写在（更新view某些原因导致的）onBindViewHolder方法中，ViewHolder该怎么写?

inner class FooterViewHolderTwo : RecyclerView.ViewHolder {
        constructor(view: View) : super(view) {
            tv = view.findViewById(R.id.tv_footer)
            tv.setOnClickListener {
                Toast.makeText(context, "I am Footer", Toast.LENGTH_SHORT).show()
            }
        }

        var tv: TextView
    }
           

注意：类FooterViewHolderTwo需要访问类RecyclerAdapter的成员context，需要用 inner 声明，不然是访问不到的哟！

接口的声明与调用

interface MyInterface {
        fun test(position: Int)
    }
var myInterface: MyInterface? = null
fun setListener(myInterface: MyInterface?) {
        this.myInterface = myInterface
    }
           

很常规的操作

至此，关于Kotlin编写RecyclerView的Adapter就已介绍完毕！