Emit: dynamically add attribute to a Type

The following Code is compiled from the official document of sl4, which has been annotated in detail. I believe everyone can understand it:

Using system; using system. reflection; using system. reflection. emit; using system. threading; namespace customattributebuildersample {public class democlass {static void main (string [] ARGs) {// obtain the new type mytype = buildtypewithcustomattributesonmethod (); // create a mytype Instance Object myinstance = activator. createinstance (mytype); // obtain all attribute objects applied on mytype [] customattrs = mytype. getcustomattributes (true); console. writeline ("custom attributes for Type 'mytype':" + "\ n"); object attrval = NULL; foreach (Object customattr in customattrs) {// obtain the Creator attribute value attrval = typeof (classcreatorattribute) in classcreatorattribute ). invokemember ("creator", bindingflags. getproperty, null, customattr, new object [] {}); console. writeline (string. format ("-- attribute: [{0 }=\" {1} \ "]", customattr, attrval) + "\ n");} console. writeline ("custom attributes for method 'helloworld () 'in 'mytype':" + "\ n"); // obtain all attributes customattrs = mytype in the helloworld method of mytype. getmember ("helloworld") [0]. getcustomattributes (true); foreach (Object customattr in customattrs) {// gets the dateupdated attribute value of datelastupdatedattribute attrval = typeof (datelastupdatedattrites ). invokemember ("dateupdated", bindingflags. getproperty, null, customattr, new object [] {}); console. writeline (string. format ("-- attribute: [{0 }=\" {1} \ "]", customattr, attrval) + "\ n");} console. writeline ("---" + "\ n"); // dynamically call the helloworld method console in the mytype instance. writeline (mytype. invokemember ("helloworld", bindingflags. invokemethod, null, myinstance, new object [] {}) + "\ n"); console. readkey ();} /// <summary> /// create a classcreatorattribute and datelastupdatedattribute type. /// </Summary> /// <returns> </returns> Public static type buildtypewithcustomattributesonmethod () {appdomain currentdomain = thread. getdomain (); assemblyname myasmname = new assemblyname (); myasmname. name = "myassembly"; // create a dynamic Program Set assemblybuilder myasmbuilder = currentdomain. definedynamicassembly (myasmname, assemblybuilderaccess. run); // dynamically create a module modulebuilder mymodbuilder = myasmbuilder. definedynamicmodule ("mymodule"); // dynamically create a type: mytype typebuilder mytypebuilder = mymodbuilder. definetype ("mytype", typeattributes. public); // define the constructor parameter type [] ctorparams = new type [] {typeof (string)}; // obtain constructorinfo classctorinfo = Typeof (classcreatorattribute ). getconstructor (ctorparams); // dynamically create classcreatorattribute customattributebuilder mycabuilder = new customattributebuilder (classctorinfo, new object [] {"Joe programmer "}); // Add the attribute dynamically created above to the (dynamically created) type mytype mytypebuilder. setcustomattrider (mycabuilder); // dynamically create a non-return value, no parameter, public method helloworld methodbuilder mymethodbuilder = mytypebuilder. definemethod ("helloworld", methoda Ttributes. public, null, new type [] {}); ctorparams = new type [] {typeof (string)}; // obtain the information of the constructor of datelastupdatedattribute classctorinfo = typeof (datelastupdatedattribute ). getconstructor (ctorparams); // dynamically create datelastupdatedattribute matmattributebuilder mycabuilder2 = new customattributebuilder (classctorinfo, new object [] {datetime. now. tostring ()}); // attaches the attribute dynamically created above to the (dynamically created) method helloworld mymet Hodbuilder. setcustomattrieline (mycabuilder2); ilgenerator myil = mymethodbuilder. getilgenerator (); myil. emitwriteline ("Hello, world! "); // In the helloworld method, creating a row is equivalent to console. Write (" Hello, world! "); Code myil. emit (Opcodes. RET); // Return Statement of the helloworld method return mytypebuilder. createtype () ;}/// <summary> // create a custom attribute, apply it to the dynamically created "type" later. // </Summary> public class classcreatorattribute: attribute {private string creator; Public String creator {get {return creator ;}} public classcreatorattribute (string name) {This. creator = Name ;}/// <summary> // create a custom attribute, apply it to the dynamically created "method" Later // </Summary> public class datelastupdatedattribute: attribute {private string dateupdated; Public String dateupdated {get {return dateupdated ;}} public datelastupdatedattridate (string thedate) {This. dateupdated = thedate ;}}}

Output result:

Custom Attributes for Type 'mytype ':

-- Attribute: [customattributebuildersample. classcreatorattribute = "Joe program mer"]

Custom Attributes for method 'helloworld () 'in 'mytype ':

-- Attribute: [customattributebuildersample. datelastupdatedattribute = "2011/11/13 21:46:31"]

---

Hello, world!