开发中遇到这个问题，想着还是总结下，刚开始只是限制UITextField的键盘为
UIKeyboardTypeASCIICapable，可是当用户切换了中文键盘后依然没解决问题，于是我给输入框加了监听事件，获取输入框最新的输入内容，检测输入的内容中是否含有中文，如果有中文就替换成空字符串，具体实现如下：
infoView.userTF.keyboardType = UIKeyboardTypeASCIICapable;
//监听输入内容
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(textFiledEditChanged:)
name:@"UITextFieldTextDidChangeNotification"
object:infoView.userTF];
-(void)textFiledEditChanged:(NSNotification*)notification
{
UITextField*textField = notification.object;
NSString*str = textField.text;
for (int i = 0; i<str.length; i++)
{
NSString*string = [str substringFromIndex:i];
NSString *regex = @"[\u4e00-\u9fa5]{0,}$"; // 中文
// 2、拼接谓词
NSPredicate *predicateRe1 = [NSPredicate predicateWithFormat:@"self matches %@", regex];
// 3、匹配字符串
BOOL resualt = [predicateRe1 evaluateWithObject:string];
if (resualt)
{
//是中文替换为空字符串
str = [str stringByReplacingOccurrencesOfString:[str substringFromIndex:i] withString:@""];
}
}
textField.text = str;
}