UIWebView体系结构（四）UIWebBrowserView

UIWebBrowserView的声明如下：（代码好长，点此跳过）

 @interface UIWebBrowserView : UIWebDocumentView <UIWebFormAccessoryDelegate, UIBrowserDocumentController, _UIWebRotationDelegate>
 {
     UIWebFormAccessory *_accessory;
     NSObject<UIFormPeripheral> *_input;
     DOMNode *_currentAssistedNode;
     DOMNode *_assistedNodeStartingFocusRedirects;
     struct CGRect _inputViewBounds;
     struct CGRect _addressViewBounds;
     float _lastAdjustmentForScroller;
     unsigned int _audioSessionCategoryOverride;
     unsigned int _accessoryEnabled:1;
     unsigned int _forceInputView:1;
     unsigned int _formIsAutoFilling:1;
     unsigned int _inputViewObeysDOMFocus:1;
     unsigned int _allowDOMFocusRedirects:1;
     unsigned int _hasEditedTextField:1;
     unsigned int _alwaysDispatchesScrollEvents:1;
     UIWebTouchEventsGestureRecognizer *_webTouchEventsGestureRecognizer;
     UIWebFormDelegate *_formDelegate;
     UIResponder *_editingDelegateForEverythingExceptForms;
     unsigned int _dispatchedTouchEvents;
     NSMutableArray *_deferredTouchEvents;
     struct {
         NSMutableArray *all;
         NSMutableArray *html;
         NSMutableArray *javascript;
         NSMutableArray *css;
         NSMutableArray *error;
         NSMutableArray *warning;
         NSMutableArray *tip;
         NSMutableArray *log;
     } _messages;
     CDStruct_d58a15aa _pdf;
 }

 + (id)_PDFPageNumberLabel:(BOOL)arg1;
 + (BOOL)isAutoFillAllowed;
 + (id)getUIWebBrowserViewForWebFrame:(id)arg1;
 + (float)preferredScrollDecelerationFactor;
 @property(readonly, nonatomic) BOOL hasEditedTextField; // @synthesize hasEditedTextField=_hasEditedTextField;
 @property(nonatomic) BOOL allowDOMFocusRedirects; // @synthesize allowDOMFocusRedirects=_allowDOMFocusRedirects;
 @property(nonatomic) BOOL inputViewObeysDOMFocus; // @synthesize inputViewObeysDOMFocus=_inputViewObeysDOMFocus;
 @property(nonatomic, getter=isAccessoryEnabled) BOOL accessoryEnabled; // @synthesize accessoryEnabled=_accessoryEnabled;
 @property(nonatomic) UIResponder *_editingDelegateForEverythingExceptForms; // @synthesize _editingDelegateForEverythingExceptForms;
 @property(retain, nonatomic) DOMNode *_currentAssistedNode; // @synthesize _currentAssistedNode;
 @property(retain, nonatomic) NSObject<UIFormPeripheral> *_input; // @synthesize _input;
 @property(retain, nonatomic) UIWebFormAccessory *_accessory; // @synthesize _accessory;
 - (BOOL)considerHeightOfRectOfInterestForRotation;
 - (struct CGSize)contentSizeForScrollView:(id)arg1;
 - (float)scaleForProposedNewScale:(float)arg1 andOldScale:(float)arg2;
 - (struct CGRect)activeRectForRectOfInterest:(struct CGRect)arg1;
 - (float)heightToKeepVisible;
 - (float)minimumVerticalContentOffset;
 - (struct CGRect)rectOfInterestForRotation;
 - (void)updateBoundariesOfScrollView:(id)arg1 withScales:(CDStruct_869f9c67)arg2;
 - (CDStruct_869f9c67)scalesForContainerSize:(struct CGSize)arg1;
 @property(nonatomic) BOOL alwaysDispatchesScrollEvents;
 - (void)webView:(id)arg1 didFirstVisuallyNonEmptyLayoutInFrame:(id)arg2;
 - (id)_absoluteUrlRelativeToDocumentURL:(id)arg1;
 - (void)_startURLificationIfNeededCoalesce:(BOOL)arg1;
 - (void)_setSelectedDOMRangeAndUpdateUI:(id)arg1;
 - (void)_clearSelectionAndUI;
 - (BOOL)_dumpWebArchiveAtPath:(id)arg1;
 - (void)_updatePDFPageNumberLabelWithUserScrolling:(BOOL)arg1 animated:(BOOL)arg2;
 - (struct CGPoint)_originForPDFPageLabelInSuperview:(id)arg1;
 - (unsigned int)_firstVisiblePDFPageNumber;
 - (void)_clearAllConsoleMessages;
 - (void)clearMessagesMatchingMask:(int)arg1;
 - (id)messagesMatchingMask:(int)arg1;
 - (void)webView:(id)arg1 addMessageToConsole:(id)arg2 withSource:(id)arg3;
 - (void)_setAddressViewFrame:(struct CGRect)arg1;
 - (void)rotateEnclosingScrollViewToFrame:(struct CGRect)arg1;
 - (struct CGSize)_defaultScrollViewContentSize;
 - (void)_zoomToRect:(struct CGRect)arg1 withScale:(float)arg2;
 - (void)_zoomToRect:(struct CGRect)arg1 ensuringVisibilityOfRect:(struct CGRect)arg2 withScale:(float)arg3 forceScroll:(BOOL)arg4 formAssistantFrame:(struct CGRect)arg5 animationDuration:(double)arg6;
 - (void)_zoomToRect:(struct CGRect)arg1 ensuringVisibilityOfRect:(struct CGRect)arg2 withScale:(float)arg3 forceScroll:(BOOL)arg4;
 - (void)_zoomToNode:(id)arg1 forceScroll:(BOOL)arg2;
 - (void)_centerRect:(struct CGRect)arg1 forSizeChange:(BOOL)arg2 withVisibleHeight:(float)arg3 pinningEdge:(int)arg4;
 - (void)_centerRect:(struct CGRect)arg1 forSizeChange:(BOOL)arg2 withVisibleHeight:(float)arg3 pinningEdge:(int)arg4 toValue:(float)arg5;
 - (struct CGRect)_activeRectForRectToCenter:(struct CGRect)arg1;
 - (void)webViewDidPreventDefaultForEvent:(id)arg1;
 - (struct CGPoint)_convertWindowPointToViewport:(struct CGPoint)arg1;
 @property(readonly, nonatomic) BOOL isDispatchingTouchEvents;
 - (void)_webTouchEventsRecognized:(id)arg1;
 - (void)_handleDeferredEvents;
 - (void)_deferWebEvent:(id)arg1;
 - (void)_endDeferringEvents;
 - (void)_startDeferringEvents;
 - (void)_dispatchWebEvent:(id)arg1;
 - (BOOL)_shouldDeferEvents;
 - (void)webView:(id)arg1 elementDidBlurNode:(id)arg2;
 - (void)webView:(id)arg1 elementDidFocusNode:(id)arg2;
 - (void)webViewFormEditedStatusHasChanged:(id)arg1;
 - (BOOL)isAutoFilling;
 - (BOOL)isAutoFillMode;
 - (void)autoFillWithElementValue;
 - (void)acceptedAutoFillWord:(id)arg1;
 - (void)webView:(id)arg1 didFirstLayoutInFrame:(id)arg2;
 - (void)webView:(id)arg1 didFailLoadWithError:(id)arg2 forFrame:(id)arg3;
 - (void)webView:(id)arg1 didFinishLoadForFrame:(id)arg2;
 - (void)webView:(id)arg1 didStartProvisionalLoadForFrame:(id)arg2;
 - (void)webView:(id)arg1 willCloseFrame:(id)arg2;
 - (void)_autoFillFrame:(id)arg1;
 - (void)_resetFormDataForFrame:(id)arg1;
 - (id)textFormElement;
 - (id)formElement;
 - (BOOL)canAutoFill;
 - (void)formDelegateHandleTextChangeWithAutoFillSuggestions:(BOOL)arg1;
 - (void)_scrollCaretToVisible:(id)arg1;
 - (void)accessoryClear;
 - (void)accessoryAutoFill;
 - (void)accessoryTab:(BOOL)arg1;
 - (void)accessoryDone;
 @property(nonatomic) unsigned int audioSessionCategoryOverride;
 @property(nonatomic) BOOL mediaPlaybackRequiresUserAction;
 @property(nonatomic) BOOL allowsInlineMediaPlayback;
 - (void)assistFormNode:(id)arg1;
 - (void)_endAllowingFocusRedirects;
 - (void)_beginAllowingFocusRedirects;
 - (void)_updateAccessory;
 - (void)_displayFormNodeInputView;
 - (void)_stopAssistingFormNode;
 - (void)setBounds:(struct CGRect)arg1;
 - (void)setFrame:(struct CGRect)arg1;
 - (void)_didScroll;
 - (void)_updateScrollerViewForInputView:(id)arg1;
 - (void)_updateFixedPositioningObjectsLayoutSoon;
 - (void)_updateFixedPositionContent;
 - (void)_updateFixedPositioningObjectsLayoutAfterVisibleGeometryChange;
 - (void)_updateFixedPositioningObjectsLayoutAfterScroll;
 - (void)_keyboardWillHide:(id)arg1;
 - (void)_keyboardWillShow:(id)arg1;
 - (void)_keyboardDidChangeFrame:(id)arg1;
 - (void)_keyboardWillChangeFrame:(id)arg1;
 - (void)_setInputViewBoundsForAutomaticKeyboardInfo:(id)arg1 adjustScrollView:(BOOL)arg2;
 - (void)_stopAssistingNode:(id)arg1;
 - (void)_startAssistingNode:(id)arg1;
 - (void)_stopAssistingKeyboard;
 - (void)_startAssistingKeyboard;
 - (void)_promptForReplace:(id)arg1;
 - (BOOL)playsNicelyWithGestures;
 - (id)_editingDelegate;
 - (void)copy:(id)arg1;
 - (BOOL)canPerformAction:(SEL)arg1 withSender:(id)arg2;
 - (id)inputView;
 - (id)inputAccessoryView;
 - (void)_handleKeyEvent:(struct __GSEvent *)arg1;
 - (BOOL)resignFirstResponder;
 - (id)textDocument;
 - (id)_keyboardResponder;
 - (BOOL)_requiresKeyboardResetOnReload;
 - (BOOL)_requiresKeyboardWhenFirstResponder;
 - (BOOL)_keepKeyboardVisibleDuringFocusRedirects;
 - (BOOL)isEditable;
 - (void)installGestureRecognizers;
 - (void)dealloc;
 - (id)initWithFrame:(struct CGRect)arg1;
 - (id)initWithWebView:(id)arg1 frame:(struct CGRect)arg2;

 @end

UIWebBrowserView并不算复杂，主要负责这些工作：

• form的自动填充
• fixed元素的位置调整
• JavaScript的手势识别，参见《iOS私有API（三） UIWebView下的手势识别器gestureRecognizer》
• 键盘弹出时的视图滚动处理，防止遮挡
• 各种信息的中转，见_messages变量
• 提供接口让UIWebView获取信息
• 为显示PDF时添加页号标签

下面想探讨一下UIWebBrowserView->UIWebDocumentView->UIWebTiledView这样的设计。

从已掌握的信息看，他们的成员变量都是使用private继承，即子类无法直接访问父类的成员变量。他们之间的关系是子类操控父类，基类的职责不会牵涉和考虑到子类，分工非常明确。由于UIWebDocumentView直接管理WebView，它的职责是有部分属于Controller的行为，例如手势事件。但是UIWebBrowserView的JavaScript手势却完全不干涉UIWebDocumentView的手势，通过别的途径来获取更高优先级的处理权。

总之，通过继承来拆分一个大类，必须做到这样才是可行的，值得借鉴。要拆分大类通常会用组合，但这里就是不用组合的优秀例子。当然，这也要求继承链里不能有分支，即基类不会有多个子类。