Kotlin实践记录

kotlin中is来判断一个对象与指定的类型是否一致：

var a: Any = "a"
if (a is String) {
    println("a是String类型")
}
if (a !is Int) {
    println("a不是Int类型")
}

Kotlin相等判断：

equals()或 ==：判断两个结构是否相等

var a = "1"
var b = "1"
if (a.equals(b)) {
    println("a 和 b 结构相等")
    // 输出结果为：a 和 b 结构相等
}

var a = 1
var b = 1
if (a == b) {
    println("a 和 b 结构相等")
    // 输出结果为：a 和 b 结构相等
}

引用相等：=== ：判断两个引用是否指向同一对象

data class User(var name: String, var age: Int)

// 设置值
var a = User("Czh", 22)
var b = User("Czh", 22)
var c = b
var d = a
// 对比两个对象的的引用
if (c === d) {
    println("a 和 b 引用相等")
} else {
    println("a 和 b 引用不相等")
}

Kotlin中的let处理：

// 使用Java
if( mVar != null ){
    mVar.function1();
}

// 使用kotlin（无使用let函数）
mVar?.function1()

// 使用kotlin（使用let函数）
// 方便了统一判空的处理 & 确定了mVar变量的作用域
mVar?.let {
       it.function1()
}

Kotlin空安全：

!!操作符将任何值转换为非空类型，若该值为空则抛出异常

var a = null
a!!
// 抛出KotlinNullPointerException

若要允许为空，可声明一个变量为可空字符串：在字符串类型后面加一个问号?

var b: String? = "b"
b = null

Kotlin中网络请求和Json解析：

Request(url).run()为Kotlin中的网络请求方式，Json解析是自己封装类的操作。

Json.get().toObject(Request(url).run(), GankNewsList::class.java).results 是将返回结果转换为具体的bean对象

DataLoader.kt 

import com.soyoungboy.kotlinapp.util.json.Json

/**
 * Created by soyoungboy on 2018/1/29.
 */
class DataLoader {

    fun getGankNewsList(date: String): List<GankNews> {
        val url = Request.BASE_URL + date
        return Json.get().toObject(Request(url).run(), GankNewsList::class.java).results
    }

    fun getGankPictureList(date: String): ArrayList<GankPicture> {
        val url = Request.BASE_URL + date
        return Json.get().toObject(Request(url).run(), GankPictureList::class.java).results
    }
}

Json.kt

package com.soyoungboy.kotlinapp.util.json

abstract class Json internal constructor() {

    abstract fun toJson(src: Any): String

    abstract fun <T> toObject(json: String, claxx: Class<T>): T

    abstract fun <T> toObject(bytes: ByteArray, claxx: Class<T>): T

    abstract fun <T> toList(json: String, claxx: Class<T>): List<T>?

    companion object {
        private var json: Json? = null

        fun get(): Json {
            if (json == null) {
                json = GsonImpl()
            }
            return json as Json
        }
    }
}

具体的json解析封装：

package com.soyoungboy.kotlinapp.util.json

import com.google.gson.Gson
import com.google.gson.reflect.TypeToken
import java.util.*

/**
 * Created by soyoungboy on 2017/12/25.
 */

class GsonImpl : Json() {
    private val gson = Gson()

    override fun toJson(src: Any): String {
        return gson.toJson(src)
    }

    override fun <T> toObject(json: String, claxx: Class<T>): T {
        return gson.fromJson(json, claxx)
    }

    override fun <T> toObject(bytes: ByteArray, claxx: Class<T>): T {
        return gson.fromJson(String(bytes), claxx)
    }

    override fun <T> toList(json: String, claxx: Class<T>): List<T>? {
        val type = object : TypeToken<ArrayList<T>>() {

        }.type
        return gson.fromJson<List<T>>(json, type)
    }

}

bean对象：

GankNewsList.kt

package com.soyoungboy.kotlinapp.bean

/**
 * Created by soyoungboy on 2018/1/29.
 */
class GankNewsList(val error: Boolean, val results: List<GankNews>)

GankNews.kt

package com.soyoungboy.kotlinapp.bean

/**
 * Created by soyoungboy on 2018/1/29.
 */
data class GankNews(val _id: String,
                    val createdAt: String,
                    val desc: String,
                    val publishedAt: String,
                    val type: String,
                    val url: String,
                    val used: Boolean,
                    val who: String)

Kotlin异步线程和主线程之间的切换

async {}为异步代码块

uiThread {}为主线程代码块

private fun getGanksNewsList() = async {
        val news = DataLoader().getGankNewsList("data/all/20/2")
        uiThread {
            forecast_list.adapter = GankNewsAdapter(news) {
                val intent = Intent()
                intent.setClass(this@GankNewsListActivity, WebActivity::class.java)
                intent.putExtra("url", it.url)
                startActivity(intent)
            }
        }

    }

kotlin跳转和数据传递：

intent跳转并携带数据：

val intent = Intent()
intent.setClass(this@GankNewsListActivity, WebActivity::class.java)
intent.putExtra("url", it.url)
startActivity(intent)

接收数据：

intent.getStringExtra("url")为接收数据操作

override fun getUrl(): String {
        return intent.getStringExtra("url")
    }

kotlin图片加载：

由于Kotlin和Java代码之间可以相互操作，所以Kotlin可以调用Android相关的图片加载库，这里用Glide举例子：

引入Glide

compile 'com.github.bumptech.glide:glide:4.1.1'
annotationProcessor 'com.github.bumptech.glide:compiler:4.1.1'
compile 'com.github.bumptech.glide:okhttp3-integration:4.0.0'

对Glide的封装

代码见：

https://github.com/soyoungboy/KotlinApp/tree/master/app/src/main/java/com/soyoungboy/kotlinapp/util/glide

调用如上ImageUtils进行图片加载缓存

class ViewHolder(val view: View, val itemClickListener: (GankPicture) -> Unit) : RecyclerView.ViewHolder(view) {
        fun bind(pictures: GankPicture) {
            val meizi = view.meizi as ImageView
            ImageUtils.loadImage(pictures.url,meizi)
            view.title.text = pictures.desc
            view.setOnClickListener {
                itemClickListener(pictures)
                view.context.longToast(pictures.url)
            }
        }
    }

kotlin之RecyclerView对应的Adapter

val items: List<GankPicture> 为要传进来进行展示的数据

view.setOnClickListener {
                itemClickListener(pictures)
                view.context.longToast(pictures.url)
            }
为点击事件

package com.soyoungboy.kotlinapp.adapter

import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import com.soyoungboy.kotlinapp.R
import com.soyoungboy.kotlinapp.bean.GankPicture
import com.soyoungboy.kotlinapp.util.glide.ImageUtils
import kotlinx.android.synthetic.main.item_meizi.view.*
import org.jetbrains.anko.longToast

/**
 * Created by soyoungboy on 2018/1/29.
 */
class GankPictureAdapter(val items: List<GankPicture>, val itemClickListener: (GankPicture) -> Unit) : RecyclerView.Adapter<GankPictureAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_meizi, parent, false)
        return ViewHolder(view, itemClickListener)
    }

    override fun getItemCount(): Int = items.size

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(items[position])
    }

    class ViewHolder(val view: View, val itemClickListener: (GankPicture) -> Unit) : RecyclerView.ViewHolder(view) {
        fun bind(pictures: GankPicture) {
            val meizi = view.meizi as ImageView
            ImageUtils.loadImage(pictures.url,meizi)
            view.title.text = pictures.desc
            view.setOnClickListener {
                itemClickListener(pictures)
                view.context.longToast(pictures.url)
            }
        }
    }
}

intent传值和返回

btn_act_response.setOnClickListener {
val response = MessageInfo(et_response.text.toString(), DateUtil.no
wTime)
val intent = Intent()
intent.putExtra("message", response)
setResult(Activity.RESULT_OK, intent)
finish()
}

//从下一个页面返回到本页面回调onActivityResult方法
override fun onActivityResult(requestCode: Int, resultCode: Int, data:
Intent?) {
if (data != null) {
//获取下一个页面的应答参数
val response = data.extras.getParcelable<MessageInfo>
("message")
tv_request.text = " 收到返回消息： \n 应答时间为
${response.send_time}\n应答内容为${response.content}"
}
}

Kotlin Spinner简化写法

通过selector来实现Android Java里面Spinner的实现，代码也变得极其简洁。

tv_spinner为布局里面的TextView控件

class SpinnerActivity : AppCompatActivity() {
    val satellites = listOf("金星", "木星", "水星", "火星")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_spinner)
        tv_spinner.text = satellites[0]
        tv_spinner.setOnClickListener {
            selector("请选择星星", satellites) { i ->
                tv_spinner.text = satellites[i]
                toast("你选择的是${tv_spinner.text}")
            }
        }

    }
}

实践的代码见我的github:https://github.com/soyoungboy/KotlinApp,里面是我学习Kotlin的一些小练习