09-008 Routing 之 DefaultInlineConstraintResolver

核心代码如下：

这个类是解析文本 如 range(5,100) 为具体的约束类 如：RangeRouteConstraint

 private readonly IDictionary<string, Type> _inlineConstraintMap;
        private readonly IServiceProvider _serviceProvider;

        public DefaultInlineConstraintResolver(IServiceProvider serviceProvider,
                                               IOptions<RouteOptions> routeOptions)
        {

			// 这里是否还记得：
			// IOptions<RouteOptions> 默认实现是 OptionManager
			// 构造函数是：  public OptionsManager(IEnumerable<IConfigureOptions<RouteOptions>> setups)
			// 如果没有配置信息 setups 没内容  Get 的时候 默认是 new RouteOptions();
			_serviceProvider = serviceProvider;
            _inlineConstraintMap = routeOptions.Options.ConstraintMap;
        }

        /// <inheritdoc />
        /// <example>
        /// A typical constraint looks like the following
        /// "exampleConstraint(arg1, arg2, 12)".
        /// Here if the type registered for exampleConstraint has a single constructor with one argument,
        /// The entire string "arg1, arg2, 12" will be treated as a single argument.
        /// In all other cases arguments are split at comma.
        /// </example>
        public virtual IRouteConstraint ResolveConstraint([NotNull] string inlineConstraint)
        {
            string constraintKey;
            string argumentString;
            var indexOfFirstOpenParens = inlineConstraint.IndexOf('(');
            if (indexOfFirstOpenParens >= 0 && inlineConstraint.EndsWith(")", StringComparison.Ordinal))
            {
				// 有参数的情况 比如:range(5,100)
				constraintKey = inlineConstraint.Substring(0, indexOfFirstOpenParens);
                argumentString = inlineConstraint.Substring(indexOfFirstOpenParens + 1,
                                                            inlineConstraint.Length - indexOfFirstOpenParens - 2);
            }
            else
            {
				// 没有参数的情况 比如 int;doube 等
				constraintKey = inlineConstraint;
                argumentString = null;
            }

            Type constraintType;
            if (!_inlineConstraintMap.TryGetValue(constraintKey, out constraintType))
            {
                // Cannot resolve the constraint key
                return null;
            }

			// 必须实现接口 IRouteConstraint
			if (!typeof(IRouteConstraint).GetTypeInfo().IsAssignableFrom(constraintType.GetTypeInfo()))
            {
                throw new InvalidOperationException(
                            Resources.FormatDefaultInlineConstraintResolver_TypeNotConstraint(
                                                        constraintType, constraintKey, typeof(IRouteConstraint).Name));
            }

			// 创建具体的约束对象 
            return CreateConstraint(constraintType, argumentString);
        }