如何在UITextView中滚动到当前光标位置？

Question

我在S.O.上搜寻了很久，想找到一个简单的解决方案来获取光标的当前位置，然后滚动到该位置（假设键盘是可见的）。大多数方法似乎都过于复杂，并且在某些情况下效果不佳。我该如何使滚动功能始终正常工作，无论光标是否在键盘下方？

- kbpontius

Answer 1

1）确保你的UITextView的contentInset已正确设置，并且在执行此操作之前，textView已经是firstResponder。 contentInset属性告诉textView哪里是用户可见区域。如果键盘可见，请确保将textView.contentInset.bottom属性设置为键盘顶部边框，否则textView可能会滚动到不可见的空间（即键盘后面）。

请参阅此S.O.帖子以获取更多信息：UIScrollView contentInset属性是用来做什么的?

2）在我的textView准备好了插图并成为firstResponder之后，我调用以下函数：

private func scrollToCursorPositionIfBelowKeyboard() {
    let caret = textView.caretRectForPosition(textView.selectedTextRange!.start)
    let keyboardTopBorder = textView.bounds.size.height - keyboardHeight!

   // Remember, the y-scale starts in the upper-left hand corner at "0", then gets
   // larger as you go down the screen from top-to-bottom. Therefore, the caret.origin.y
   // being larger than keyboardTopBorder indicates that the caret sits below the
   // keyboardTopBorder, and the textView needs to scroll to the position.
   if caret.origin.y > keyboardTopBorder {
        textView.scrollRectToVisible(caret, animated: true)
    }
 }

可选：如果您只想将滚动条滚动到光标的当前位置（假设textView当前为firstResponder并且contentInset已经在此之前正确设置），只需调用：

[self.textView scrollRangeToVisible:self.textView.selectedRange];

private func scrollToCursorPosition() {
    let caret = textView.caretRectForPosition(textView.selectedTextRange!.start)
    textView.scrollRectToVisible(caret, animated: true)
 }

额外信息：为了将textView滚动条设置为合适的高度，请通过修改scrollIndicatorInsets来进行操作，例如：

// This is not relative to the coordinate plane. You simply set the `.bottom` property 
// as if it were a normal height property. The textView does the rest for you.
textView.contentInset.bottom = keyboardHeight 
textView.scrollIndicatorInsets = textView.contentInset // Matches textView's visible space.

- kbpontius