tutorial on how the. NET MYMVC Framework assigns values to methods

People who have used reflection know that invoking a method is simple, but how do you prepare an incoming parameter for an "unsigned" method?
To answer this question, please follow the getactioncallparameters implementation process:

private static object[] Getactioncallparameters (HttpContext context, actiondescription action) {if (action. Parameters = = NULL | | Action.    Parameters.length = = 0) return null; object[] Parameters = new Object[action.    Parameters.length]; for (int i = 0; I < action. Parameters.length; i++) {ParameterInfo p = action.        Parameters[i];        if (p.isout) continue; if (P.parametertype = = typeof (NameValueCollection)) {if (string. Compare (P.name, "Form", stringcomparison.ordinalignorecase) = = 0) Parameters[i] = context.            Request.Form; else if (string. Compare (P.name, "QueryString", stringcomparison.ordinalignorecase) = = 0) Parameters[i] = context.            Request.QueryString; else if (string. Compare (P.name, "Headers", stringcomparison.ordinalignorecase) = = 0) Parameters[i] = context.            Request.headers; else if (string. Compare (P.name, "ServerVariables", stringcomparison.ordinalIgnoreCase) = = 0) Parameters[i] = context.        Request.ServerVariables;            } else{Type Paramtertype = P.parametertype.getrealtype (); If the argument is a simple type, it is read directly from the HttpRequest and assigned the value if (Paramtertype.issimpletype ()) {Object val = modelhelper. Getvaluebykeyandtypefrommrequest (context.                Request, p.name, paramtertype, NULL);            if (val! = null) parameters[i] = val; } else {//custom type.                Create the instance first, and then assign values to all the members.                Note: Custom types for nested types are not supported here.                Object item = Activator.CreateInstance (Paramtertype); Modelhelper.fillmodel (context.                Request, item, p.name);            Parameters[i] = Item; }}} return parameters;}

To understand this code also starts with the "procedure for finding an action" in the previous section, at which point you can get a description of the action, which is represented as a actiondescription type within the framework:

Internal sealed class actiondescription:basedescription{public    controllerdescription Pagecontroller; Leave public    MethodInfo MethodInfo {get; private set for pageaction;}    Public Actionattribute Attr {get; private set;}    Public parameterinfo[] Parameters {get; private set;}    public bool Hasreturn {get; private set;}    Public Actiondescription (MethodInfo m, Actionattribute atrr): Base (m)    {this        . MethodInfo = m;        This. Attr = ATRR;        This. Parameters = M.getparameters ();        This. Hasreturn = m.returntype! = Reflectionhelper.voidtype;    }}

In the third line of code of the constructor, I can get all the parameters of this method.
Then I can iterate over the definition of each parameter in the Getactioncallparameters method and assign a value to them.
This code also explains the previous reason for supporting only 4 types of NameValueCollection collections.

Note that when I get the type of each parameter, I use the following statement:

Type Paramtertype = P.parametertype.getrealtype ();

In fact, ParameterType has already reflected the type of the parameter, why not use it directly?
Answer: Because of the "can be vague" reason. We need special treatment for this type.
For example, if a parameter is declared like this: int? Id
So, even if you include an ID in QueryString, I can't go straight to int? With this type, you must get the "actual type" of it.
Getrealtype () is an extension method that specifically accomplishes this function:

<summary>///gets an actual type (excluding the effects of the nullable type). For example: int? Finally will get int///</summary>///<param name= "type" ></param>///<returns></returns>public Static type Getrealtype (this type type) {    if (type). Isgenerictype)        return Nullable.getunderlyingtype (type)?? type;    else        return type;}

If the type of a parameter is a custom type, the framework creates an instance (calling the parameterless constructor) and assigns a value to its property, field.

Note: For custom types, be sure to provide an argument-free constructor.

The code for populating a data member for an instance of a custom type is as follows:

Internal static class modelhelper{public static readonly bool Isdebugmode; Static Modelhelper () {compilationsection configsection = configurationmanager.getsection ("s        Ystem.web/compilation ") as compilationsection;    if (configsection! = null) Isdebugmode = Configsection.debug;    }///<summary>//fill in a data entity according to HttpRequest.    Data entities of nested types are not supported here, and data members are required to be simple data types.    </summary>//<param name= "Request" ></param>//<param name= "model" ></param>  public static void Fillmodel (HttpRequest request, object model, string paramname) {Modeldescripton Descripton = Reflectionhelper.getmodeldescripton (model.        GetType ());        Object val = null; foreach (DataMember field in Descripton.            Fields) {//This implementation does not support data entities of nested types.            If there is a need for this, you can change this to a recursive nested call. val = getvaluebykeyandtypefrommrequest (Request, field. Name, Field.            Type.getrealtype (), paramname); if (val! = null) field.        SetValue (model, Val); }}///<summary> read an HTTP parameter value. Here only read QueryString and form///</summary>//<param name= "Request" ></param>//<param name= "Ke Y "></param>///<returns></returns> public static string Gethttpvalue (HttpRequest request, Stri ng key) {string val = Request.        Querystring[key]; if (val = = null) val = Request.        Form[key];    return Val; public static object Getvaluebykeyandtypefrommrequest (HttpRequest request, string key, Ty PE type, string paramname) {//Does not support complex type if (type.        Issimpletype () = = false) return null;        String val = gethttpvalue (request, key); if (val = = null) {//try again.            There may be more than one custom type, and the form element is prefixed with the variable name. if (string. IsNullOrEmpty (paramname) = = False) {val = GethttpvaLue (Request, ParamName + "." + key);        } if (val = = null) return null; } return Safechangetype (val.    Trim (), type); The public static object Safechangetype (string value, Type conversiontype) {if (Conversiontype = = typeof (Strin        g)) return value; if (value = = NULL | | value.        Length = = 0)//An empty string cannot be converted at all, so it returns null return null directly;            try {//For simplicity, call methods in the. NET Framework directly.            If the conversion fails, an exception is thrown.        return Convert.changetype (value, conversiontype);            } catch {if (isdebugmode) throw;    Throw exception in Debug mode else return null; Ignore exception in release mode (prevents malicious user from wrong Input)}}}

Before loading data to a custom data type instance, you need to know what properties and fields the instance object has, and the code for this process is as follows:

<summary>///returns the description information for an entity type (all properties and fields). </summary>///<param name= "type" ></param>///<returns></returns>public static Modeldescripton Getmodeldescripton (Type type) {    if (type = null)        throw new ArgumentNullException ("type");        String key = Type. FullName;    Modeldescripton mm = (Modeldescripton) S_modeltable[key];    if (mm = = null) {        list<datamember> List = new list<datamember> ();        (from P in type.) GetProperties (BindingFlags.Instance | BindingFlags.Public)         Select New Propertymember (P)). ToList (). ForEach (x=>list. ADD (x));        (from F in type.) GetFields (BindingFlags.Instance | BindingFlags.Public)         Select New Fieldmember (f)). ToList (). ForEach (x = list. ADD (x));        MM = new Modeldescripton {fields = list. ToArray ()};        S_modeltable[key] = mm;    }    return mm;}

After getting all the properties of a type and the description of the field, it is possible to querystring,form to read the required data by the name of the data member in a circular way.

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