Iphone 限制输入到UITextField的字符数

我有一个UITextField，其中我限制输入超过2位数字。现在，它工作正常，但当我点击文本字段并选择所有内容，然后键入时，它不允许我重写现有的2位数字

关于如何在此处使用“selectedTextRange”属性的任何线索

- (BOOL)cell:(RunnerTableViewCell *)iCell shouldChangeCharactersInRange:(NSRange)iRange replacementString:(NSString *)iString {
    self.navigationItem.rightBarButtonItem.enabled = YES;
    NSCharacterSet *anUnacceptedInput = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    int aCharacterUpperLimit = 2;
    BOOL aReturnValue = YES;

    NSInteger aTotalLength = iCell.inputField.text.length + [iString length];
    NSLog(@"iString=%@ aTotalLength=%d",iString,aTotalLength);
    if ([[iString componentsSeparatedByCharactersInSet:anUnacceptedInput] count] > 1 || (aTotalLength > aCharacterUpperLimit && ![iString isEqualToString:kRunnerEmptyString]) || [iString length] > aCharacterUpperLimit) {
        aReturnValue = NO;
    }
    return aReturnValue;
}

试试这个：

NSInteger aTotalLength = iCell.inputField.text.length + [iString length] - iRange.length;