iOS textfield 限制输入字数长度

[self.textFiled addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];

-(void)textFieldDidChange:(UITextField *)textField
{
CGFloat maxLength = 14;
NSString *toBeString = textField.text;

//获取高亮部分
UITextRange *selectedRange = [textField markedTextRange];
UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
if (!position || !selectedRange)
{
if (toBeString.length > maxLength)
{
NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:maxLength];
if (rangeIndex.length == 1)
{
textField.text = [toBeString substringToIndex:maxLength];
}
else
{
NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, maxLength)];
textField.text = [toBeString substringWithRange:rangeRange];
}
}
}
}