不多说，坑爹的玩意，直接上代码：

static const NSInteger kMaxLength = 10;

1.[_textField addTarget:self action:@selector(textFieldChange) forControlEvents:UIControlEventEditingChanged];

2.

//限定主题字数 10个

- (void)textFieldChange{

    NSString *toBeString = self.textField.text;

    NSString *lang = [[UITextInputMode currentInputMode] primaryLanguage];

    if([lang isEqualToString:@"zh-Hans"]){ //简体中文输入，包括简体拼音，健体五笔，简体手写

        UITextRange *selectedRange = [self.textField markedTextRange];

        UITextPosition *position = [self.textField positionFromPosition:selectedRange.start offset:0];

        if (!position){//非高亮

            if (toBeString.length > kMaxLength) {

                [self.view makeToast:@"您最多可以输入10个字" duration:1 position:@"top"];

                self.textField.text = [toBeString substringToIndex:kMaxLength];

            }

        }

    }else{//中文输入法以外

        if (toBeString.length > kMaxLength) {

            [self.view makeToast:@"您最多可以输入10个字" duration:1 position:@"top"];

            self.textField.text = [toBeString substringToIndex:kMaxLength];

        }

    }

}

UITextField限制输入字数高亮状态下输入框内真实类容与textFiled（解决中文输入问题）