开发笔记:预加载多个本地WebView

篇首语：本文由编程笔记#小编为大家整理，主要介绍了预加载多个本地WebView相关的知识，希望对你有一定的参考价值。

首先，你应该切换到WKWebView，UIVewView是no longer recommended供Apple使用。

其次，您可以创建一个Web视图池，这些视图会在应用程序启动时被创建并要求加载。这样，当用户切换到Web界面时，Web视图可能有机会完全加载。

为此你可以使用这样的类：

/// Keeps a cache of webviews and starts loading them the first time they are queried
class WebViewPreloader {
var webviews = [URL: WKWebView]()
/// Registers a web view for preloading. If an webview for that URL already
/// exists, the web view reloads the request
///
/// - Parameter url: the URL to preload
func preload(url: URL) {
webview(for: url).load(URLRequest(url: url))
}
/// Creates or returns an already cached webview for the given URL.
/// If the webview doesn't exist, it gets created and asked to load the URL
///
/// - Parameter url: the URL to prefecth
/// - Returns: a new or existing web view
func webview(for url: URL) -> WKWebView {
if let cachedWebView = webviews[url] { return cachedWebView }
let webview = WKWebView(frame: .zero)
webview.load(URLRequest(url: url))
webviews[url] = webview
return webview
}
}


并要求它在app启动期间有时预加载url：

// extension added for convenience, as we'll use the index url in at least
// two places
extension Bundle {
var indexURL: URL { return self.url(forResource: "index", withExtension: "html")! }
}
webviewPreloader.preload(url: Bundle.main.indexURL)


第三，您可能需要在控制器中使用容器视图而不是实际的Web视图：

@IBOutlet weak var webviewContainer: UIView!


剩下的就是在需要时将预加载的Web视图添加到容器中：

func loadWebview() {
// retrieve the preloaded web view, add it to the container
let webview = webviewPreloader.webview(for: Bundle.main.indexURL)
webview.frame = webviewContainer.bounds
webview.translatesAutoresizingMaskIntoCOnstraints= true
webview.autoresizingMask = [.flexibleWidth, .flexibleHeight]
webviewContainer.addSubview(webview)
}


而不是最后，请注意保持Web视图的实例可能会带来性能损失 - 内存和CPU。