- 阅读此文需要对Kotlin基本语法有所了解。
- 本文只是一个Kotlin简单开发Android Demo入手的文章，不对Kotlin语法特点进行探讨。
此Demo用到Kotlin基本知识点回顾：
一.定义变量：
var:修饰可变变量，如：var a : Int = 0 or var textView : TextView ?= null
val：修饰常量，如：val b = 1 【此后b不能再被重新赋值】
二.伴生对象的使用：
语法特点：
companion object {
...
//此方法可用来定义java中 静态常量等【此Demo用到】
//val WEB_URL="http://www.baidu.com"
// 类似于在java类中直接定义的常量 static final String WEB_URL="http://www.baidu.com"
}
三.扩展函数【不扩展说明】
四.语法特点：
var textView : TextView ?= null
textView=findViewById(R.id.u_text_id) as TextView
textView?.text?:"null"
- 上述代码第三行代码类似于 Java 中
textView==null？“null”：textView.getText().toString().isEmpty()?"null" :textView.getText().toString();
开始写Android小Demo
1.用AS创建我们的项目取名为WebViewByKotlin:
- 修改app目录下的buid.gradle,给项目添加依赖：
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
dependencies {
. . .
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}
- 修改整个项目的buid.gradle，加入如下依赖包：
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
dependencies {
classpath 'com.android.tools.build:gradle:2.3.3'
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
2.开始写activity_main.xml 代码如下：
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/web_view_container"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
3.写MainActivity.kt代码：
class MainActivity : AppCompatActivity() {
//定义变量
private var mWebView: WebView? = null
private var mExitTime = 0L
companion object {
// 定义WebView首页地址[伴生对象]
//定义static final
val WEB_URL = "http://www.baidu.com"
val TAG=MainActivity::class.simpleName //定义Log的TAG
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportActionBar!!.hide() //隐藏ActionBar
initAndSetupView()
}
// 初始化对象
fun initAndSetupView() {
val webViewContainer = findViewById(R.id.web_view_container) as FrameLayout
val params = FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT)
mWebView = WebView(applicationContext)
webViewContainer.addView(mWebView, params)
var webSettings = mWebView!!.settings
webSettings.javaScriptEnabled = true
webSettings.javaScriptCanOpenWindowsAutomatically = true
webSettings.allowFileAccess = true// 设置允许访问文件数据
webSettings.setSupportZoom(true)//支持缩放
webSettings.javaScriptCanOpenWindowsAutomatically = true
webSettings.cacheMode = WebSettings.LOAD_NO_CACHE
webSettings.domStorageEnabled = true
webSettings.databaseEnabled = true
mWebView!!.setOnKeyListener(OnKeyEvent)
mWebView!!.setWebViewClient(webClient)
mWebView!!.loadUrl(WEB_URL)
}
private val webClient = object : WebViewClient() {
override fun shouldOverrideUrlLoading(view: WebView?, url: String?): Boolean {
Log.d(TAG, url)
return false
}
}
private val OnKeyEvent = View.OnKeyListener { v, keyCode, event ->
val action = event.action
val webView = v as WebView
if (KeyEvent.ACTION_DOWN == action && KeyEvent.KEYCODE_BACK == keyCode) {
if (webView?.canGoBack()) {
webView.goBack()
return@OnKeyListener true
}
}
false
}
override fun onBackPressed() {
if ((System.currentTimeMillis() - mExitTime) > 2000) {
showToast("连按两下退出应用")
//showToast("连按两下退出应用",Toast.LENGTH_SHORT) //此种方法调用也可以 有点可变参数的意思在里面
mExitTime = System.currentTimeMillis()
} else {
super.onBackPressed()
}
}
override fun onResume() {
super.onResume()
mWebView?.onResume()
}
override fun onPause() {
super.onPause()
mWebView?.onPause()
}
override fun onDestroy() {
super.onDestroy()
mWebView?.clearCache(true)
(mWebView?.parent as FrameLayout).removeView(mWebView)
mWebView?.stopLoading()
mWebView?.setWebViewClient(null)
mWebView?.setWebChromeClient(null)
mWebView?.removeAllViews()
mWebView?.destroy()
mWebView = null
}
//扩展函数
fun MainActivity.showToast(message: String, length: Int = Toast.LENGTH_SHORT) {
Toast.makeText(this, message, length).show()
}
}
*mWebView？.xxx 操作 代码验证后 得出类似于java中
if (mWebView != null) {
mWebView.xxx;
}
