我试图在处理新的文本条目后，通过按键击键，将NSAttributedString样式应用于UITextField。问题是，每当我替换文本时，光标将在每次更改时跳到最后。这是我目前的做法......
立即接收并显示文本更改（当我返回false时同样的问题适用并手动执行文本替换）
func textField(textField: UITextField!, shouldChangeCharactersInRange range: NSRange, replacementString string: String!) -> Bool {
let range:NSRange = NSRange(location: range.location, length: range.length)
let newString = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string);
return true
}
我订阅了UITextFieldTextDidChangeNotification通知。这会触发样式。当文本被更改时，我使用一些format（）函数将其替换为格式化版本（NSAttributedString）（NSString）。
func textFieldTextDidChangeNotification(userInfo:NSDictionary) {
var attributedString:NSMutableAttributedString = NSMutableAttributedString(string: fullString)
attributedString = format(textField.text) as NSMutableAttributedString
textField.attributedText = attributedString
}
造型效果很好。但是，在每次文本替换后，光标会跳转到字符串的末尾。如何关闭此行为或手动将光标移回到开始编辑的位置？ ...或者在编辑时是否有更好的解决方案来设置文本样式？
使这项工作的方法是获取光标的位置，更新字段内容，然后将光标替换为其原始位置。我不确定Swift中的确切等价物，但以下是我在Obj-C中的做法。
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
UITextPosition *beginning = textField.beginningOfDocument;
UITextPosition *cursorLocation = [textField positionFromPosition:beginning offset:(range.location + string.length)];
textField.text = [textField.text stringByReplacingCharactersInRange:range withString:string];
/* MAKE YOUR CHANGES TO THE FIELD CONTENTS AS NEEDED HERE */
// cursorLocation will be (null) if you're inputting text at the end of the string
// if already at the end, no need to change location as it will default to end anyway
if(cursorLocation)
{
// set start/end location to same spot so that nothing is highlighted
[textField setSelectedTextRange:[textField textRangeFromPosition:cursorLocation toPosition:cursorLocation]];
}
return NO;
}
这是一个老问题，但我遇到了类似的问题并使用以下Swift解决了这个问题：
// store the current cursor position as a range
var preAttributedRange: NSRange = textField.selectedRange
// apply attributed string
var attributedString:NSMutableAttributedString = NSMutableAttributedString(string: fullString)
attributedString = format(textField.text) as NSMutableAttributedString
textField.attributedText = attributedString
// reapply the range
textField.selectedRange = preAttributedRange
它适用于我的应用程序环境，希望它对某人有用！
通过Objective-C中的代码感谢@ Stonz2。它就像一个魅力！我在Swift项目中使用它。 Swift中的相同代码：
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
let positionOriginal = textField.beginningOfDocument
let cursorLocation = textField.positionFromPosition(positionOriginal, offset: (range.location + NSString(string: string).length))
/* MAKE YOUR CHANGES TO THE FIELD CONTENTS AS NEEDED HERE */
if(cursorLocation != nil) {
textField.selectedTextRange = textField.textRangeFromPosition(cursorLocation!, toPosition: cursorLocation!)
}
return false
}
为了补充这个线程中的其他正确答案，这里有一些Swift 4.2以及UITextField和UITextView的代码片段。
的UITextField
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
// Update Cursor
let positionOriginal = textField.beginningOfDocument
let cursorLocation = textField.position(from: positionOriginal, offset: (range.location + string.count))
if let cursorLocation = cursorLocation {
textField.selectedTextRange = textField.textRange(from: cursorLocation, to: cursorLocation)
}
return false
}
的UITextView
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
// Update Cursor
let positionOriginal = textView.beginningOfDocument
let cursorLocation = textView.position(from: positionOriginal, offset: (range.location + text.count))
if let cursorLocation = cursorLocation {
textView.selectedTextRange = textView.textRange(from: cursorLocation, to: cursorLocation)
}
return false
}
这是一个为swift 2工作的代码。尽情享受吧！
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
let beginnig: UITextPosition = textField.beginningOfDocument
if let txt = textField.text {
textField.text = NSString(string: txt).stringByReplacingCharactersInRange(range, withString: string)
}
if let cursorLocation: UITextPosition = textField.positionFromPosition(beginnig, offset: (range.location + string.characters.count) ) {
textField.selectedTextRange = textField.textRangeFromPosition(cursorLocation, toPosition: cursorLocation)
}
return false
}
请注意，最后“if let”应始终保留在代码的末尾。
为了回答这里不同问题的答案：https://stackoverflow.com/a/51814368/431271，你不应该修改shouldChangeCharactersInRange中的文本，因为该委托方法只是为了让字段知道是否允许更改而不应该变异。
相反，我喜欢通过订阅值更改来处理文本更改，如下所示：
textField.addTarget(self, action: #selector(handleTextChanged), for: .editingChanged)
// elsewhere in the file
func handleTextChanged(_ textField: UITextField) {
textField.sanitizeText(map: formatText)
}
sanitizeText的实现看起来像这样：
extension UITextField {
// Use this to filter out or change the text value without
// losing the current selection
func sanitizeText(map: ((String) -> String)) {
guard let text = self.text,
let selection = selectedTextRange else {
return
}
let newText = map(text)
// only execute below if text is different
guard newText != text else { return }
// determine where new cursor position should start
// so the cursor doesnt get sent to the end
let diff = text.count - newText.count
let cursorPosition = offset(from: beginningOfDocument, to: selection.start) - diff
self.text = newText
// notify the value changed (to ensure delegate methods get triggered)
sendActions(for: .valueChanged)
// update selection afterwards
if let newPosition = position(from: beginningOfDocument, offset: cursorPosition) {
selectedTextRange = textRange(from: newPosition, to: newPosition)
}
}
}