Kotlin初步代码编写

• 类和构造函数
  

Kotlin创建类的方式与Java类似,如创建Person类：

class Person{    var name: String? = ""    var age: Int = 0}

可以看到，Kotlin的变量声明方式略有些不同。另外，为了实现“空安全”，Kotlin对可以为空的变量和不可以为空的变量作了区分。在上述代码中，变量age不可为空，而？表明变量name可以为空。下面创建实例（注，Kotlin实例时没有关键字new，实例完就可以直接赋值了）：

var person = Person()person.name= "yoyo"person.age = 22

构造函数在Kotlin创建非常简单(注，这个类没有任何内容可以省略大括号)，如下：

class Person(var name: String?, var age: Int)

构造函数的函数体你可以写在init块中：

class Person(var name: String?, var age: Int){     init{        ...    }}

• Kotlin编写类
  

从下面图可以看出可以创建Activity、file、class的kt文件

下面编写一个RecyclerView展示集合类HomeFragment.kt，由于xml比较简单就不贴出来了：

class HomeFragment : Fragment() {    private var persons: List<Person>? = null    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {        return inflater!!.inflate(R.layout.fragment_home,container,false)    }    override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {        super.onViewCreated(view, savedInstanceState)        getData()        val recyclerView : RecyclerView = view!!.findViewById(R.id.recycler_view) as RecyclerView        recyclerView.layoutManager = LinearLayoutManager(activity!!)        recyclerView.addItemDecoration(DividerDecoration(activity))        //java写的适配器//        val adapter: HomeAdapter = HomeAdapter(activity, persons!!)        //kotlin写的适配器        val adapter: HomeKtAdapter = HomeKtAdapter(activity, persons!!)        recyclerView.adapter = adapter    }    /**     * mock数据     */     private fun getData(): List<Person> {        persons = listOf(                Person("html", 12),                Person("kotlin", 36),                Person("java", 12),                Person(null, 12),                Person("android", 12),                Person("ios", 12),                Person("c++", 12),                Person("php", 12)        )        return persons as List<Person>    }}

如你所见，我们定义类一个变量并转型为RecyclerView。这里与Java有点不同，LayoutManager、adapter等会通过属性的方式被设置，而不是通过set;
List的创建也与java不一样，现在简单的可以通过使用一个函数创建一个常量的List，它就会自动推断出结果的类型。

这里为了体现kotlin与java代码互通，这里写了两个适配器，一个是用java写的HomeAdapter.java，另一个是用kotlin写的HomeKtAdapter.kt

Java写的适配器HomeAdapter.java：

/** * HomeAdapter * Created by chen_yong on 2017/5/24. */public class HomeAdapter extends RecyclerView.Adapter<HomeAdapter.ViewHolder> {    private List<Person> persons;    private LayoutInflater inflater;    public HomeAdapter(Context mContext,List<Person> persons) {        this.persons = persons;        this.inflater = LayoutInflater.from(mContext);    }    @Override    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        return new ViewHolder(inflater.inflate(R.layout.home_item,parent,false));    }    @Override    public void onBindViewHolder(ViewHolder holder, int position) {        Person person = persons.get(position);        holder.tv_name.setText(person.getName());        holder.tv_age.setText(String.valueOf(person.getAge()));    }    @Override    public int getItemCount() {        return persons.size();    }    class ViewHolder extends RecyclerView.ViewHolder{        TextView tv_name;        TextView tv_age;        public ViewHolder(View itemView) {            super(itemView);            tv_name = (TextView) itemView.findViewById(R.id.name);            tv_age = (TextView) itemView.findViewById(R.id.age);        }    }}

Kotlin写的适配器HomeKtAdapter.kt

/** * HomektAdapter * Created by chen_yong on 2017/5/24. */ class HomeKtAdapter(mContext: Context, private val persons: List<Person>) : RecyclerView.Adapter<HomeKtAdapter.ViewHolder>() {    private val inflater: LayoutInflater = LayoutInflater.from(mContext)    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {        return ViewHolder(inflater.inflate(R.layout.home_item, parent, false))    }    override fun onBindViewHolder(holder: ViewHolder, position: Int) {        val person = persons[position]        holder.tv_name.text = person.name        holder.tv_age.text = person.age.toString()    }    override fun getItemCount(): Int {        return persons.size    }    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {        var tv_name: TextView = itemView.findViewById(R.id.name) as TextView        var tv_age: TextView = itemView.findViewById(R.id.age) as TextView    }}

• 效果展示
  

从下面图就可以体现出安全性，字段为空不做判断也不会报错

点击Demo下载