UITextField字数限制，监听通知
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitLength:) name:UITextViewTextDidChangeNotification object:nil];//限制字数
-(void)limitLength:(NSNotification*)obj{
NSInteger kMaxLength = 7;
UITextField *textField = (UITextField *)obj.object;
NSString *toBeString = textField.text;
NSString *lang = [textField.textInputMode primaryLanguage];
if ([lang isEqualToString:@"zh-Hans"])// 简体中文输入
{
//获取高亮部分
UITextRange *selectedRange = [textField markedTextRange];
UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
// 没有高亮选择的字，则对已输入的文字进行字数统计和限制
if (!position)
{
if (toBeString.length > kMaxLength)
{
textField.text = [toBeString substringToIndex:kMaxLength];
}
}
}
// 中文输入法以外的直接对其统计限制即可，不考虑其他语种情况
else
{
if (toBeString.length > kMaxLength)
{
NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:kMaxLength];
if (rangeIndex.length == 1)
{
textField.text = [toBeString substringToIndex:kMaxLength];
}
else
{
NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, kMaxLength)];
textField.text = [toBeString substringWithRange:rangeRange];
}
}
}
}