Flutter 插件url_launcher简介

url_launcher是用于在移动平台中启动URL的Flutter插件，适用于IOS和Android平台。他可以打开网页，发送邮件，还可以拨打电话。

github地址：https://github.com/flutter/plugins/tree/master/packages/url_launcher

最近项目需求就是打开一个连接跳转到安卓或苹果默认的浏览器。虽然开始一个简单的要求，其中的一个细节就是执行打开网页这一操作后，不能看上去像在应用内部打开，看上去要在应用外部打开。pub.dev提供了加载网页的插件url_launcher；所谓的插件也是用安卓和苹果原生代码实现的，对插件的代码进行解压可以看到。

加载网页的方式：

_launchURL() async {
 const url = '要加载的网页地址';
 if (await canLaunch(url)) {
 await launch(url);
 }
}

简单查看一下插件的源码：

Future<bool> launch(
 String urlString, {
 bool forceSafariVC,
 bool forceWebView,
 bool enableJavaScript,
 bool enableDomStorage,
 bool universalLinksOnly,
 Map<String, String> headers,
 Brightness statusBarBrightness,
 }) async {
 assert(urlString != null);
 ........................................

属性：forceSafariVC 

/// [forceSafariVC] is only used in iOS with iOS version >= 9.0. By default (when unset), the launcher
/// opens web URLs in the Safari View Controller, anything else is opened
/// using the default handler on the platform. If set to true, it opens the
/// URL in the Safari View Controller. If false, the URL is opened in the
/// default browser of the phone. Note that to work with universal links on iOS,
/// this must be set to false to let the platform's system handle the URL.
/// Set this to false if you want to use the cookies/context of the main browser
/// of the app (such as SSO flows). This setting will nullify [universalLinksOnly]
/// and will always launch a web content in the built-in Safari View Controller regardless
/// if the url is a universal link or not.

forceSafariVC 仅被用于IOS版本为0.9和0.9以上的系统。默认情况下不设置，如果设置加载网页连接在Safari视图控制器打开，其他操作系统打开使用默认设置。如果设置为true，在Safari视图控制器打开URL。如果设置为false，在手机默认浏览器中打开。注意网页连接在IOS 平台操作系统上打开必须设置为false。如果你想去用cookies在app网页端实现登录需要设置为false。

如果加载在内置Safari视图控制器的网页内容是universal link或不是，设置universalLinksOnly无效。

Universal Link：（点击连接打开应用）参考、参考

属性：forceWebView

/// [forceWebView] is an Android only setting. If null or false, the URL is
/// always launched with the default browser on device. If set to true, the URL
/// is launched in a WebView. Unlike iOS, browser context is shared across
/// WebViews.

该属性只在安卓平台设置。如果设置为false或不设置，网络地址被加载在设备默认浏览器。如果设置为true，网络地址被加载在自定义WebView。ios系统的浏览器可以共享数据。

属性：enableJavaScript

/// [enableJavaScript] is an Android only setting. If true, WebView enable
/// javascript.

该属性只在安卓平台设置。如果为true，webview可加载脚步。

属性：enableDomStorage

/// [enableDomStorage] is an Android only setting. If true, WebView enable
/// DOM storage.

该属性只在安卓平台设置。如果为true，webView加载本地网页缓存。

属性：universalLinksOnly

/// [universalLinksOnly] is only used in iOS with iOS version >= 10.0. This setting is only validated
/// when [forceSafariVC] is set to false. The default value of this setting is false.
/// By default (when unset), the launcher will either launch the url in a browser (when the
/// url is not a universal link), or launch the respective native app content (when
/// the url is a universal link). When set to true, the launcher will only launch
/// the content if the url is a universal link and the respective app for the universal
/// link is installed on the user's device; otherwise throw a [PlatformException].

该属性只在IOS平台使用并且IOS版本为10.0或10.0以上。当前该属性设置成false生效。默认值是false。默认情况下，通过手机手机浏览器加载网页（当这个链接不是一个universal link）或 加载各自app（当这个链接是一个universal link，点击进行下载应用包）。如果设置属性值为true，如果这个连接是一个universal link并且各自的应用通过这个universal link安装在用户的设备上，那么改网页会被加载。否则抛出PlatformException。

属性：statusBarBrightness

/// [statusBarBrightness] Sets the status bar brightness of the application
/// after opening a link on iOS. Does nothing if no value is passed. This does
/// not handle resetting the previous status bar style.

设置的状态栏亮度在IOS应用打开一个连接后可以看到。如果没有设置该属性不会有效果的。状态栏样式重复设置以第一次设置为准。

Future<bool> launch(
 String urlString, {
 bool forceSafariVC,
 bool forceWebView,
 bool enableJavaScript,
 bool enableDomStorage,
 bool universalLinksOnly,
 Map<String, String> headers,
 Brightness statusBarBrightness,
 }) async {
 assert(urlString != null);
 final Uri url = Uri.parse(urlString.trimLeft());
 final bool isWebURL = url.scheme == 'http' || url.scheme == 'https';
 if ((forceSafariVC == true || forceWebView == true) && !isWebURL) {
 throw PlatformException(
 code: 'NOT_A_WEB_SCHEME',
 message: 'To use webview or safariVC, you need to pass'
  'in a web URL. This $urlString is not a web URL.');
 }
 bool previousAutomaticSystemUiAdjustment;
 if (statusBarBrightness != null && defaultTargetPlatform == TargetPlatform.iOS) {
 previousAutomaticSystemUiAdjustment =
 WidgetsBinding.instance.renderView.automaticSystemUiAdjustment;
 WidgetsBinding.instance.renderView.automaticSystemUiAdjustment = true;
 SystemChrome.setSystemUIOverlayStyle(statusBarBrightness == Brightness.light
 ? SystemUiOverlayStyle.dark
 : SystemUiOverlayStyle.light);
 }
 final bool result = await UrlLauncherPlatform.instance.launch(
 urlString,
 useSafariVC: forceSafariVC ?? isWebURL,
 useWebView: forceWebView ?? false,
 enableJavaScript: enableJavaScript ?? false,
 enableDomStorage: enableDomStorage ?? false,
 universalLinksOnly: universalLinksOnly ?? false,
 headers: headers ?? <String, String>{},
 );
 if (statusBarBrightness != null) {
 WidgetsBinding.instance.renderView.automaticSystemUiAdjustment =
 previousAutomaticSystemUiAdjustment;
 }
 return result;
}

安卓或苹果平台加载：

实现让用户看到不少应用内部跳转打开网页加载，是跳转到手机默认浏览器加载。

if (Platform.isIOS) {
  launch(url, forceSafariVC: false, forceWebView: true);
  return;
 }
 if (Platform.isAndroid) {
  launch(url);
 }

解压插件源码可以看到Flutter就是调用安卓或者ios原生代码进行加载网页。

安卓中通过webview加载网页或者跳转默认浏览器加载网页：

LaunchStatus launch(
 String url,
 Bundle headersBundle,
 boolean useWebView,
 boolean enableJavaScript,
 boolean enableDomStorage) {
 if (activity == null) {
 return LaunchStatus.NO_ACTIVITY;
 }

 Intent launchIntent;
 if (useWebView) {
 launchIntent =
  WebViewActivity.createIntent(
  activity, url, enableJavaScript, enableDomStorage, headersBundle);
 } else {
 launchIntent =
  new Intent(Intent.ACTION_VIEW)
  .setData(Uri.parse(url))
  .putExtra(Browser.EXTRA_HEADERS, headersBundle);
 }

 activity.startActivity(launchIntent);
 return LaunchStatus.OK;
 }

在ios手机中默认浏览器打开

- (void)launchURLInVC:(NSString *)urlString result:(FlutterResult)result API_AVAILABLE(ios(9.0)) {
 NSURL *url = [NSURL URLWithString:urlString];
 self.currentSession = [[FLTURLLaunchSession alloc] initWithUrl:url withFlutterResult:result];
 __weak typeof(self) weakSelf = self;
 self.currentSession.didFinish = ^(void) {
 weakSelf.currentSession = nil;
 };
 [self.topViewController presentViewController:self.currentSession.safari
     animated:YES
     completion:nil];
}

在ios中用内置浏览器打开：

- (void)launchURL:(NSString *)urlString
  call:(FlutterMethodCall *)call
  result:(FlutterResult)result {
 NSURL *url = [NSURL URLWithString:urlString];
 UIApplication *application = [UIApplication sharedApplication];

 if (@available(iOS 10.0, *)) {
 NSNumber *universalLinksOnly = call.arguments[@"universalLinksOnly"] ?: @0;
 NSDictionary *options = @{UIApplicationOpenURLOptionUniversalLinksOnly : universalLinksOnly};
 [application openURL:url
   options:options
 completionHandler:^(BOOL success) {
  result(@(success));
 }];
 } else {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
 BOOL success = [application openURL:url];
#pragma clang diagnostic pop
 result(@(success));
 }
}

如果在安卓或者苹果加载http网页出现无法加载：

///安卓：在xml文件夹下创建network_security_config.xml ，然后在AndroidManifest.xml 标签application引用

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
 <base-config cleartextTrafficPermitted="true">
 <trust-anchors>
  <certificates src="system" />
 </trust-anchors>
 </base-config>
</network-security-config>
///IOS：

参考：

Android WebView：https://developer.android.google.cn/guide/webapps/webview?hl=zh_cn

SafariServices：https://developer.apple.com/documentation/safariservices

总结

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