(ios): allow to set "preferredContentMode" (#688)

PreferredContentMode can now be set with preference config. Since iPadOS came out iPads get a desktop Safari useragent by default.

see #687 

Co-authored-by: Tim Brust <github@timbrust.de>

README.md

@@ -176,6 +176,16 @@ At the moment the only supported target in OSX is `_system`.
 
 `_blank` and `_self` targets are not yet implemented and are ignored silently. Pull requests and patches to get these to work are greatly appreciated.
 
+### iOS Quirks
+
+Since the introduction of iPadOS 13, iPads try to adapt their content mode / user agent for the optimal browsing experience. This may result in iPads having their user agent set to Macintosh, making it hard to detect them as mobile devices using user agent string sniffing. You can change this with the `PreferredContentMode` preference in `config.xml`.
+
+```xml
+<preference name="PreferredContentMode" value="mobile" />
+```
+
+The example above forces the user agent to contain `iPad`. The other option is to use the value `desktop` to turn the user agent to `Macintosh`.
+
 ### Browser Quirks
 
 - Plugin is implemented via iframe,

src/ios/CDVWKInAppBrowser.m

@@ -757,6 +757,15 @@ - (void)createViews
         configuration.mediaPlaybackRequiresUserAction = _browserOptions.mediaplaybackrequiresuseraction;
     }
 
+    if (@available(iOS 13.0, *)) {
+        NSString *contentMode = [self settingForKey:@"PreferredContentMode"];
+        if ([contentMode isEqual: @"mobile"]) {
+            configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeMobile;
+        } else if ([contentMode  isEqual: @"desktop"]) {
+            configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeDesktop;
+        }
+
+    }
 
 
     self.webView = [[WKWebView alloc] initWithFrame:webViewBounds configuration:configuration];