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