feat(ios): Add iOS contentMode property (#1538 by @TheAlmightyBob)

This allows overriding iPadOS 13's desktop-class browsing to load mobile content instead of desktop content.

Co-authored-by: Jamon Holmgren <jamonholmgren@gmail.com>

apple/RNCWebView.h

 @property (nonatomic, assign) BOOL ignoreSilentHardwareSwitch;
 @property (nonatomic, copy) NSString * _Nullable allowingReadAccessToURL;
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000 /* iOS 13 */
+@property (nonatomic, assign) WKContentMode contentMode;
+#endif
+
 + (void)setClientAuthenticationCredential:(nullable NSURLCredential*)credential;
 + (void)setCustomCertificatesForHost:(nullable NSDictionary *)certificates;
 - (void)postMessage:(NSString *_Nullable)message;

apple/RNCWebView.m

   }
   wkWebViewConfig.userContentController = [WKUserContentController new];
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000 /* iOS 13 */
+  if (@available(iOS 13.0, *)) {
+    WKWebpagePreferences *pagePrefs = [[WKWebpagePreferences alloc]init];
+    pagePrefs.preferredContentMode = _contentMode;
+    wkWebViewConfig.defaultWebpagePreferences = pagePrefs;
+  }
+#endif
+
   // Shim the HTML5 history API:
   [wkWebViewConfig.userContentController addScriptMessageHandler:[[RNCWeakScriptMessageDelegate alloc] initWithDelegate:self]
                                                             name:HistoryShimName];

apple/RNCWebViewManager.m

 @interface RNCWebViewManager () <RNCWebViewDelegate>
 @end
 
+@implementation RCTConvert (WKWebView)
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000 /* iOS 13 */
+RCT_ENUM_CONVERTER(WKContentMode, (@{
+    @"recommended": @(WKContentModeRecommended),
+    @"mobile": @(WKContentModeMobile),
+    @"desktop": @(WKContentModeDesktop),
+}), WKContentModeRecommended, integerValue)
+#endif
+@end
+
 @implementation RNCWebViewManager
 {
   NSConditionLock *_shouldStartLoadLock;
 RCT_EXPORT_VIEW_PROPERTY(contentInsetAdjustmentBehavior, UIScrollViewContentInsetAdjustmentBehavior)
 #endif
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000 /* iOS 13 */
+RCT_EXPORT_VIEW_PROPERTY(contentMode, WKContentMode)
+#endif
+
 /**
  * Expose methods to enable messaging the webview.
  */

docs/Reference.md

 - [`overScrollMode`](Reference.md#overscrollmode)
 - [`contentInset`](Reference.md#contentinset)
 - [`contentInsetAdjustmentBehavior`](Reference.md#contentInsetAdjustmentBehavior)
+- [`contentMode`](Reference.md#contentMode)
 - [`dataDetectorTypes`](Reference.md#datadetectortypes)
 - [`scrollEnabled`](Reference.md#scrollenabled)
 - [`directionalLockEnabled`](Reference.md#directionalLockEnabled)
 
 ---
 
+### `contentMode`[⬆](#props-index)<!-- Link generated with jump2header -->
+
+Controls the type of content to load. Available on iOS 13 and later. Defaults to `recommended`, which loads mobile content on iPhone & iPad Mini but desktop content on larger iPads.
+
+See [Introducing Desktop-class Browsing on iPad](https://developer.apple.com/videos/play/wwdc2019/203/) for more.
+
+Possible values:
+
+- `recommended`
+- `mobile`
+- `desktop`
+
+| Type   | Required | Platform |
+| ------ | -------- | -------- |
+| string | No       | iOS      |
+
+---
+
 ### `dataDetectorTypes`[⬆](#props-index)<!-- Link generated with jump2header -->
 
 Determines the types of data converted to clickable URLs in the web view's content. By default only phone numbers are detected.

src/WebViewTypes.ts

   always = 'always'
 };
 
+export declare type ContentMode = 'recommended' | 'mobile' | 'desktop';
+
 export interface IOSNativeWebViewProps extends CommonNativeWebViewProps {
   allowingReadAccessToURL?: string;
   allowsBackForwardNavigationGestures?: boolean;
   bounces?: boolean;
   contentInset?: ContentInsetProp;
   contentInsetAdjustmentBehavior?: ContentInsetAdjustmentBehavior;
+  contentMode?: ContentMode;
   readonly dataDetectorTypes?: DataDetectorTypes | DataDetectorTypes[];
   decelerationRate?: number;
   directionalLockEnabled?: boolean;
    */
   contentInset?: ContentInsetProp;
 
+  /**
+   * Defaults to `recommended`, which loads mobile content on iPhone
+   * and iPad Mini but desktop content on other iPads.
+   * 
+   * Possible values are:
+   * - `'recommended'`
+   * - `'mobile'`
+   * - `'desktop'`
+   * @platform ios
+   */
+  contentMode?: ContentMode;
+
   /**
    * Determines the types of data converted to clickable URLs in the web view's content.
    * By default only phone numbers are detected.