概述
Kotlin DSL（領(lǐng)域特定語言）是一種使用 Kotlin 語言編寫的，專門用于解決特定問題領(lǐng)域的語言。DSL 的優(yōu)點在于其代碼易讀、易寫，因為它的語法和領(lǐng)域問題的語法更接近。此外，Kotlin 的強大類型系統(tǒng)和靈活性使得創(chuàng)建 DSL 變得更加容易。
使用DSL構(gòu)建HTML
在使用DSL構(gòu)建HTML時，我們首先需要定義一個接口：
interface IElement {
// 拼接HTML字符串，每個元素都需要實現(xiàn)
fun render(builder: StringBuilder, indent: String): String
}然后，我們需要實現(xiàn)一個基礎(chǔ)元素類，這個類需要傳入標簽名和內(nèi)容。每個元素都有標簽名，如<p>hello</p>、<img />?；A(chǔ)元素類的代碼如下：
open class BaseElement(val tagName: String, val content: String = "") : IElement {
// 省略部分代碼...
}接下來，我們需要實現(xiàn)各種HTML元素，如<html>、<head>、<title>、<body>、<h1>、<p>、<a>、<img>等。這些元素的實現(xiàn)代碼如下：
// <html>標簽
class Html() : BaseElement("html") {
// 省略部分代碼...
}
// <head>標簽
class Head : BaseElement("head") {
// 省略部分代碼...
}
// <title>標簽
class Title(content: String) : BaseElement("title", content)
// <body>標簽
class Body : BaseElement("body") {
// 省略部分代碼...
}
// <h1>標簽
class H1(content: String) : BaseElement("h1", content)
// <p>標簽
class P(content: String) : BaseElement("p", content)
// <a>標簽
class A(content: String) : BaseElement("a", content) {
var href: String
get() = attributes["href"]!!
set(value) {
attributes["href"] = value
}
}
// <img>標簽
class Img : BaseElement("img") {
var src: String
get() = attributes["src"]!!
set(value) {
attributes["src"] = value
}
var alt: String
get() = attributes["alt"]!!
set(value) {
attributes["alt"] = value
}
override fun render(builder: StringBuilder, indent: String): String {
return builder.append("$indent<$tagName")
.append(renderAttributes())
.append(" />\n")
.toString()
}
}最后，我們可以在實際的應(yīng)用中使用這些DSL構(gòu)建HTML，如下所示：
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val webView: WebView = findViewById(R.id.webView)
val htmlStr = getHtmlStr()
webView.loadData(htmlStr, "text/html", "UTF-8")
}
private fun getHtmlStr(): String {
return html {
head {
title {
"hello Kotlin"
}
}
body {
h1 {
"hello world DSL"
}
p {
"--------------------------"
}
img(
src = "https://img-home.yssmx.com/images/20201124032511.png",
alt = "hello DSL"
)
p {
"=========================="
}
a(href = "https://blog.csdn.net/qq_14876133") {
"Kotlin"
}
}
}()
}
}/**
* 需要傳入標簽名和內(nèi)容
* 每個元素都有標簽名，如：<p>hello</p>、<img />
*/open class BaseElement(val tagName: String, val content: String = "") : IElement {
private val children = mutableListOf<BaseElement>() //元素內(nèi)的所有子元素
private val _attributes = mutableMapOf<String, String>() //元素的屬性名和屬性值
protected val attributes get() = _attributes protected fun addElement(element: BaseElement) {
this.children.add(element)
}
protected fun renderAttributes(): String {
val builder = StringBuilder()
if (attributes.isNotEmpty()) {
for ((attrName, attrValue) in attributes) {
builder.append(""" $attrName="$attrValue"""")
}
}
return builder.toString()
}
override fun render(builder: StringBuilder, indent: String): String {
builder.append("$indent<$tagName")
builder.append(renderAttributes())
builder.append(">\n")
if (content.isNotBlank()) {
builder.append(" $indent$content\n")
}
children.forEach {
it.render(builder, " $indent")
}
builder.append("$indent</$tagName>\n")
return builder.toString()
}
operator fun invoke(): String {
val builder = StringBuilder()
return render(builder, "")
}}實現(xiàn)子元素：
fun html(block: Html.() -> Unit): Html {
val html = Html()
html.block()
return html}// <html>標簽class Html() : BaseElement("html") {
fun head(block: Head.() -> Unit): Head {
val head = Head()
head.block()
addElement(head)
return head }
fun body(block: Body.() -> Unit): Body {
val body = Body()
body.block()
addElement(body)
return body }}// <head>標簽class Head : BaseElement("head") {
fun title(block: () -> String): Title {
val content = block()
val title = Title(content)
addElement(title)
return title }}// <title>標簽class Title(content: String) : BaseElement("title", content)// <body>標簽class Body : BaseElement("body") {
fun h1(block: () -> String): H1 {
val content = block()
val h1 = H1(content)
addElement(h1)
return h1 }
fun p(block: () -> String): P {
val content = block()
val p = P(content)
addElement(p)
return p }
fun a(href: String = "", block: () -> String): A {
val content = block()
val a = A(content).apply {
this.href = href }
addElement(a)
return a }
fun img(src: String = "", alt: String = ""): Img {
val img = Img().apply {
this.src = src this.alt = alt }
addElement(img)
return img }}// <h1>標簽class H1(content: String) : BaseElement("h1", content)// <p>標簽class P(content: String) : BaseElement("p", content)// <a>標簽class A(content: String) : BaseElement("a", content) {
var href: String get() = attributes["href"]!!
set(value) {
attributes["href"] = value }}// <img>標簽class Img : BaseElement("img") {
var src: String get() = attributes["src"]!!
set(value) {
attributes["src"] = value }
var alt: String get() = attributes["alt"]!!
set(value) {
attributes["alt"] = value }
override fun render(builder: StringBuilder, indent: String): String {
return builder.append("$indent<$tagName")
.append(renderAttributes())
.append(" />\n")
.toString()
}}使用：
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val webView: WebView = findViewById(R.id.webView)
val htmlStr = getHtmlStr()
webView.loadData(htmlStr, "text/html", "UTF-8")
}
private fun getHtmlStr(): String {
return html {
head {
title {
"hello Kotlin"
}
}
body {
h1 {
"hello world DSL"
}
p {
"--------------------------"
}
img(
src = "https://img-home.yssmx.com/images/20201124032511.png",
alt = "hello DSL"
)
p {
"=========================="
}
a(href = "https://blog.csdn.net/qq_14876133") {
"Kotlin"
}
}
}()
}}效果：
文章來源：http://www.zghlxwxcb.cn/news/detail-725155.html
輸出的html字符串：文章來源地址http://www.zghlxwxcb.cn/news/detail-725155.html
<html> <head> <title> hello Kotlin </title> </head> <body> <h1> hello world DSL </h1> <p> -------------------------- </p> <img src="https://img-home.yssmx.com/images/20201124032511.png" alt="hello DSL" /> <p> ========================== </p> <a href="https://blog.csdn.net/qq_14876133"> Kotlin </a> </body> </html>
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