objective-c – 如何仅在UITextField中输入数字并限制最大长度？

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRangE)range replacementString:(NSString *)String  {


    NSUInteger newLength = [textField.text length] + [String length] - range.length;

    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersinstring:numbERS_ONLY] invertedSet];

    NSString *filtered = [[String componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];

    while (newLength < CHARACTER_LIMIT) {
        return [String isEqualToString:filtered];
    }

/* Limits the no of characters to be enter in text field */

    return (newLength > CHARACTER_LIMIT ) ? NO : YES; 

}

不是我不喜欢 the answer I wrote at this question,那也是 copy & pasted这里.我会尝试解释你的错误.

这个答案是基于你的常量定义如下的假设：

#define numbERS_ONLY @"1234567890"
#define CHARACTER_LIMIT 3

您的逻辑失败的原因是,当newLength将等于CHARACTER_LIMIT时,您永远不会处理该事件.

为了说明你的文本框是空的,你要求将字符串@“ABC”粘贴到文本域,你的委托方法被调用.您创建过滤的字符串,正确计算为空字符串,您不能等待执行行return [String isEqualToString：filtered];但是,由于newLength为3,因此您不符合while循环的条目要求,所以您从未真正评估该行.所以简单的return(newLength> CHARACTER_LIMIT)？不：是决定返回值.

如果您的CHARACTER_LIMIT由于某种原因实际上为4,则只需将“ABCD”设为逻辑仍然适用的字符串即可.

这是一个简单的例子,您的功能更正了工作.再次,我假设CHARACTER_LIMIT等于3.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRangE)range replacementString:(NSString *)String  {
    NSUInteger newLength = [textField.text length] + [String length] - range.length;
    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersinstring:numbERS_ONLY] invertedSet];
    NSString *filtered = [[String componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
    return (([String isEqualToString:filtered])&&(newLength <= CHARACTER_LIMIT));
}