用RAC监听文本框输入字数

@weakify(self);
    [[[self.textField.rac_textSignal map:^id(NSString *value) {
        return @(value.length);
    }] filter:^BOOL(id value) {
        return [value intValue] > 10;
    }] subscribeNext:^(id x) {
        @strongify(self);
        [SVProgressHUD showErrorWithStatus:@"输入文字长度已经10个了, 不能再输入了"];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [SVProgressHUD dismiss];
        });
        self.textField.text = [self.textField.text substringToIndex:maxLenght];
    }];