笔者性懒，腹中无墨
app嵌html屡见不鲜, 本文描述加载简单的html网页。
首先说明需求: 有网的状态直接从获取html网页并且缓存, 无网状态先从缓存读取html, 若不成功则加载本地html文件, 并且将本地html文件写入缓存, 以便下次读取.
缓存html.png
1.加载html网页, viewWillAppear或者viewDidLoad.
以下QAUrl均为html完整的url
func loadHtml() {
guard let url: URL = URL(string: QAUrl) else {return}
webView.loadRequest(URLRequest(url: url))
}
2.若成功, 就在成功的代理方法里, 将网页端html写入缓存
func writeToCache() {
let queue = DispatchQueue(label: "writeToCache")
queue.async {
let htmlResponseStr = try? String(contentsOf: URL(string: self.QAUrl)!, encoding: .utf8)
let fileManager = FileManager.default
let cachesPath = NSSearchPathForDirectoriesInDomains(.cachesDirectory, .userDomainMask, true).last
try? fileManager.createDirectory(atPath: (cachesPath?.appending("/Caches"))!, withIntermediateDirectories: true, attributes: nil)
guard let path = cachesPath?.appending("/Caches/feedback.html") else{return}
print("缓存网页html路径: \(path)")
do {
try htmlResponseStr?.write(toFile: path, atomically: true, encoding: .utf8)
} catch {
return
}
}
}
3.不成功,在失败的代理方法里, 加载磁盘缓存或者本地html,其中isNetConnected是指是否连接到互联网, 默认是true,加载失败后置为false.
fileprivate var isNetConnected: Bool = true // 是否连接到互联网
func loadCachesOrLocalHtml() {
isNetConnected = false
let cachesPath = NSSearchPathForDirectoriesInDomains(.cachesDirectory, .userDomainMask, true).last
guard let path = cachesPath?.appending("/Caches/feedback.html") else {return}
do {
let htmlString = try? String(contentsOfFile: path, encoding: .utf8)
guard let localPath = htmlString else {
guard let path = Bundle.main.path(forResource: "qa", ofType: "html", inDirectory: nil) else {return}
guard let htmlString = try? String(contentsOfFile: path, encoding: .utf8) else {return}
// 本地
webView.loadHTMLString(htmlString, baseURL: nil)
writeLocalToCache()
return
}
// 磁盘缓存
webView.loadHTMLString(localPath, baseURL: nil)
}
}
4.同样,此次成功后,在代理方法里,将本地html文件写入缓存
func writeLocalToCache() {
let queue = DispatchQueue(label: "writeLocalToCache")
queue.async {
guard let path = Bundle.main.path(forResource: "qa", ofType: "html", inDirectory: nil) else {return}
guard let htmlString = try? String(contentsOfFile: path, encoding: .utf8) else {return}
let fileManager = FileManager()
let cachesPath = NSSearchPathForDirectoriesInDomains(.cachesDirectory, .userDomainMask, true).last
try? fileManager.createDirectory(atPath: (cachesPath?.appending("/Caches"))!, withIntermediateDirectories: true, attributes: nil)
guard let localPath = cachesPath?.appending("/Caches/feedback.html") else{return}
print("缓存本地html路径: \(localPath)")
do {
try htmlString.write(toFile: localPath, atomically: true, encoding: .utf8)
} catch {
return
}
}
}
5.代理方法的里很简洁
// MARK: - 网页或者本地html加载完成 都会调用
func webViewDidFinishLoad(_ webView: UIWebView) {
if isNetConnected {
writeToCache()
}
}
func webView(_ webView: UIWebView, didFailLoadWithError error: Error) {
loadCachesOrLocalHtml()
}
6.需要注意的是
(1)拼接缓存地址时, 如果html的URL类似于"http://10.0.4.2:82/app/qa.html",不能作为地址拼接,否则无法缓存.
(2)笔者将拼接地址统一写成"/Caches/feedback.html",若有新的缓存,则地址被覆盖,不会导致缓存多个相同文件,一般无需清理或者导致内存警告
(3)本文不涉及缓存图片, js交互等问题
7.补充:
开发过程中,笔者又遇到了一个问题,有网的情况下,网页也可能出现加载不成功.这个时候如果只是加载网页就会什么都没有.所以在viewWillAppear或者viewDidLoad里应该有个判断
DispatchQueue.global().async {
WebService.request("/app/qa.html").validate().responseData { response in
let finish = response.result.isSuccess
DispatchQueue.main.async {
if finish {
self.loadHtml()
} else {
self.loadCachesOrLocalHtml()
}
}
}
}
如果请求request返回的finish是true即成功,则加载html网页,不成功则加载缓存.