iOS - UITextView实现原理

open class UITextView : UIScrollView, UITextInput, UIContentSizeCategoryAdjusting {}

UITextView继承于UIScrollView, UITextInput, UIContentSizeCategoryAdjusting，当然UIScrollView继承于UIView，UIView继承于UIResponder。

所以我们从UITextView的View hierarchy和Responder chain来分析。

View hierarchy

1. UITextView
2. UITextContainerView
3. UITextSelectionView(出现光标的时候会有这个View)

Responder

UITextView对UITouch的处理主要是靠如下几个GestureRecognizer。

<UIScrollViewDelayedTouchesBeganGestureRecognizer: 0x12ed4a540;
state = Possible; 
delaysTouchesBegan = YES; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=delayed:,target=<SealFooDemo.SLTextView 0x12f81fa00>)>>

<UIScrollViewPanGestureRecognizer: 0x12ed4aff0;
state = Possible;
delaysTouchesEnded = NO; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=handlePan:, target=<SealFooDemo.SLTextView 0x12f81fa00>)>>

<UITextTapRecognizer: 0x12ed55e70; 
state = Possible; 
delaysTouchesEnded = NO; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=oneFingerDoubleTap:, target=<UITextInteractionAssistant 0x12ed55800>)>;
numberOfTapsRequired = 2>

<UITapAndAHalfRecognizer: 0x12ed56d40; 
state = Possible; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=tapAndAHalf:, target=<UITextInteractionAssistant 0x12ed55800>)>>

<UITextTapRecognizer: 0x12ed588a0; 
state = Possible; 
delaysTouchesEnded = NO; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=oneFingerTap:, target=<UITextInteractionAssistant 0x12ed55800>)>>

<UIVariableDelayLoupeGesture: 0x12ed58ed0; 
state = Possible; 
delaysTouchesEnded = NO; 
view = <SealFooDemo.SLTextView 0x12f81fa00>;
target= <(action=loupeGesture:, target=<UITextInteractionAssistant 0x12ed55800>)>>

这里的UITextTapRecognizer是UITapGestureRecognizer的子类，但是在UIKit里面却找不到，还不知道原因。

for gestureRecognizer:UIGestureRecognizer in self.textView.gestureRecognizers! {
    print(gestureRecognizer.cancelsTouchesInView)
}

执行上面代码的结果都是True，因为所有UIGestureRecognizer的cancelsTouchesInView默认都是false，这样只要是有UIGestureRecognizer的地方，view都是拿不到被识别走的UITouch的。