how to generate and print barcode in c# windows application Lesson 3: Reflecting Types in Visual C#.NET

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Lesson 3: Reflecting Types
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When you output the type names for the three instances, you get the name of the type that was created, not the local variable:
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Typename for anAnimal is Animal Typename for dogAnimal is Dog Typename for catAnimal is Cat
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Why is this An object is always of a single type. The fact that it can be cast to one of its base types or to one of the interfaces it implements does not change that the object is still of one and only one type.
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Enumerating Class Members
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Within the Type class, there are methods for getting different parts of a Type, including methods, properties, fields, and events. Each of these parts of a Type is represented by a class within the reflection system that ends with the name Info. Therefore, the class that represents a field is called FieldInfo, the class that represents an event is called EventInfo, and so on. All these info classes derive from a common abstract class called MemberInfo. In fact, the Type class also derives from the MemberInfo class. The MemberInfo class contains common functionality. Most of the interesting data about each of the members of a type is contained in the derived classes. As you saw earlier in the explanation of the Type class, a number of methods on the Type class allow you to get each of the parts of the type. These match the info classes as well. For example, the GetEvent and GetEvents methods return an EventInfo object (or objects), and the GetField and GetFields methods return a FieldInfo object (or objects). So iterating through each of these parts of the Type is very straightforward. For example, to enumerate all the properties of a class, you could write code like so:
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' VB For Each prop As PropertyInfo In t.GetProperties() Console.WriteLine(" {0}", prop.Name) Next // C# foreach (PropertyInfo prop in t.GetProperties()) { Console.WriteLine(" {0}", prop.Name); }
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In addition to parts of a type, a Type class supports returning types that are nested within a type. These can be nested classes, interfaces, enumerations, and so on. You can get at these by calling the GetNestedType or GetNestedTypes method. These methods return Type objects instead of a specialized info class. Because the Type class
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Reflection
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derives from the MemberInfo class, the type class is really an info class anyway. You can get at nested types like so:
' VB For Each nestedType As Type In t.GetNestedTypes() Console.WriteLine(" {0}", nestedType.Name) Next // C# foreach (Type nestedType in t.GetNestedTypes()) { Console.WriteLine(" {0}", nestedType.Name); }
In addition, you can iterate through all the parts of a Type by using the GetMembers call. This method, which is shown in the following example, returns an array of MemberInfo objects:
' VB For Each member As MemberInfo In t.GetMembers() Console.WriteLine(" {0}: {1}", member.MemberType, member.Name) Next // C# foreach (MemberInfo member in t.GetMembers()) { Console.WriteLine(" {0}: {1}", member.MemberType, member.Name); }
Each of these info classes has a specialized use for working with part of the Type object. Table 14-9 shows each of these MemberInfo derived classes and what objects they represent.
Table 14-9
MemberInfo Derived Classes
Name ConstructorInfo EventInfo FieldInfo LocalVariableInfo MethodBase
Description Represents a constructor. Represents an event. Represents a field. Represents a local variable inside a method s body. Represents any member that can contain code. This includes methods and constructors. This is the actual base class for ConstructorInfo and MethodInfo.
Lesson 3: Reflecting Types
Table 14-9 MemberInfo Derived Classes
Name MethodInfo PropertyInfo
Description Represents a method. Represents a property. Properties are accompanied by methods for the get and/or set operations that are specified for a property. Represents a single type in the system. It can be a nested type within another type or a stand-alone type.
Type
You can see the type of member each of these MemberInfo objects is by checking the MemberType enumeration on the MemberInfo class. This enumeration contains all the different types of members that a MemberInfo object can represent. You can also cast the MemberInfo objects into their derived form, like so:
' VB If (member.MemberType = MemberTypes.Property) Then Dim prop As PropertyInfo = CType(member,PropertyInfo) Console.WriteLine(" Property Type: {0}", prop.PropertyType.Name) End If // C# if (member.MemberType == MemberTypes.Property) { PropertyInfo prop = (PropertyInfo)member; Console.WriteLine(" Property Type: {0}", prop.PropertyType.Name); }
Enumerating through members of a type allowed you to find only publicly available members. It also returned all publicly available members whether they were static members or instance members. Finally, it only supported returning all the members that the class has, including those that it inherited. To allow more control over the retrieval of type members, the reflection system supports an enumeration where you can decide what members to return. This feature is called the BindingFlags enumeration.
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