UITextField输入长度限制

方法一：
添加UIControlEventEditingChanged事件处理

• 添加事件

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

• 实现- textFieldDidChange:方法

#define kLimitLenth 11
- (void)textFieldDidChange:(UITextField *)textField
{
    UITextRange *selectedRange = textField.markedTextRange;
    if (!selectedRange || selectedRange.empty) {
        //这里取到textfielf.text最后的值 进行检索
        //NSLog(@"selectedRange textField.text [%@]", textField.text);
        NSString *text = textField.text;
        NSUInteger len = kLimitLenth;
        if (text.length >= len) {
            textField.text = [text substringToIndex:len];
            text = textField.text;
        }    
    }
}

方法二：
设置委托 - textField: shouldChangeCharactersInRange:replacementString来处理

#define kLimitLenth 11
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (range.length >= 1) {
       return YES;
    }
    
    UITextRange *selectedRange = textField.markedTextRange;
    if (!selectedRange || selectedRange.empty) {
        NSString *text = textField.text;
        NSMutableString *mString = [NSMutableString stringWithString:text];
        [mString insertString:string atIndex:range.location];
        NSUInteger len = kLimitLenth;
        if (mString.length >= len) {
            textField.text = [mString substringToIndex:len];
            return NO;
        }
    }
    
    return YES;
}