Swift iOS ： 在webview的当前网页上提取信息的方法
使用UIWebView装载一个网页后，可能需要提取其内的信息，比较好的方法是使用JavaScript。方法UIWebView.stringByEvaluatingJavaScript可以执行一个脚本。
提取页面信息
执行如下代码，点击页面左上方的run js按钮，可以显示一个对话框，内容为当前网页的标题（title）：
import UIKit
class Page: UIViewController{
var c : UIWebView!
override func viewDidLoad() {
super.viewDidLoad()
c = UIWebView()
c.frame = super.view.frame
view.addSubview(c)
c.frame.origin.y += 100
c.frame.size.height = 300
let url = URL(string:"http://apple.com")
let ro = URLRequest(url:url!)
c.loadRequest(ro)
let button = UIButton()
button.setTitle("run js", for: .normal)
button.addTarget(self, action: #selector(tap), for: .touchDown)
button.frame = CGRect(x: 0, y: 70, width: 100, height: 20)
view.addSubview(button)
}
func tap(){
c.stringByEvaluatingJavaScript(from: "function showtitle(){alert(document.title)};showtitle()")
}
}
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window!.rootViewController = Page()
self.window?.makeKeyAndVisible()
return true
}
}如果javas使用的函数或者模块比较大，可以把它们放到一个文件内，作为资源包含，启动时加载并求值。这样是很方便的。接下来的案例，把上面案例的js函数showtitle()作为资源文件。首先func tap内修改为从资源中加载：
func tap(){
let jsCode = try! String(contentsOf: URL(fileURLWithPath: Bundle.main.path(forResource: "pack", ofType: "js")!))
c.stringByEvaluatingJavaScript(from: jsCode)
c.stringByEvaluatingJavaScript(from: "showtitle()")
}其次，创建一个资源文件，名为pack.js ,内容为：
function showtitle(){alert(document.title)};代码运行后，点击run js按钮，效果和前一个案例相同。
提取图片信息
有时候，需要截获WebView的手势操作到当前代码内，在此代码中获取当前手势触控的位置上的元素。这个场景下，就可以把js模块代码放到资源文件内，在触控代码中对此js调用和求值，获得它的输出：
import UIKit
class Page: UIViewController,UIGestureRecognizerDelegate{
var c : UIWebView!
var tapGesture : UITapGestureRecognizer!
override func viewDidLoad() {
super.viewDidLoad()
c = UIWebView()
c.frame = super.view.frame
view.addSubview(c)
c.frame.origin.y += 100
c.frame.size.height = 300
let url = URL(string:"https://httpbin.org/image/png")//must be a https url ,otherwise iOS will fobidden it
let ro = URLRequest(url:url!)
c.loadRequest(ro)
let button = UIButton()
button.setTitle("run js", for: .normal)
button.addTarget(self, action: #selector(tap), for: .touchDown)
button.frame = CGRect(x: 0, y: 70, width: 100, height: 20)
view.addSubview(button)
tapGesture = UITapGestureRecognizer(target: self, action:#selector(tapHandler(_:)))
self.tapGesture!.delegate = self
self.c.addGestureRecognizer(self.tapGesture!);
}
func tap(){
let jsCode = try! String(contentsOf: URL(fileURLWithPath: Bundle.main.path(forResource: "pack", ofType: "js")!))
c.stringByEvaluatingJavaScript(from: jsCode)
c.stringByEvaluatingJavaScript(from: "showtitle()")
}
func gestureRecognizer(_: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith shouldRecognizeSimultaneouslyWithGestureRecognizer:UIGestureRecognizer) -> Bool
{
return true
}
func tapHandler(_ tap :UITapGestureRecognizer){
let tapPoint = tap.location(in: tap.view)
print(tapPoint)
let script = String(format: "getHTMLElementAtPoint(%i,%i)", Int(tapPoint.x),Int(tapPoint.y))
let imgSrc = self.c.stringByEvaluatingJavaScript(from: script)
print(imgSrc)
}
}
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window!.rootViewController = Page()
self.window?.makeKeyAndVisible()
return true
}
}执行代码，点击页面的图片，就可以看到控制台上的输出：
(168.0, 65.0)
Optional("https://httpbin.org/image/png,100,100,110,0")委托方法 gestureRecognizer( :shouldRecognizeSimultaneouslyWith)是非常必要的，没有它的话，WebView会自己处理手势，而不是转移控制器给tapHandler( :)。
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文章和留言都翻到11页了 没有OOM
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朋友，翻页到11页，及以后，会出现OOM，无法访问
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搞个gitee的项目
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版本号是多少，你可以下载哪个代码仓库，jdk选1.8 直接跑就行
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