What is Assembly?
Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the context of an assembly.
Assemblies are a fundamental part of programming with the .NET Framework. An assembly performs the following functions:
• It contains code that the common language runtime executes. Microsoft intermediate language (MSIL) code in a portable executable (PE) file will not be executed if it does not have an associated assembly manifest. Note that each assembly can have only one entry point (that is, DllMain, WinMain, or Main).
• It forms a security boundary. An assembly is the unit at which permissions are requested and granted.
• It forms a type boundary. Every type's identity includes the name of the assembly in which it resides. A type called MyType loaded in the scope of one assembly is not the same as a type called MyType loaded in the scope of another assembly.
• It forms a reference scope boundary. The assembly's manifest contains assembly metadata that is used for resolving types and satisfying resource requests. It specifies the types and resources that are exposed outside the assembly. The manifest also enumerates other assemblies on which it depends.
• It forms a version boundary. The assembly is the smallest versionable unit in the common language runtime; all types and resources in the same assembly are versioned as a unit. The assembly's manifest describes the version dependencies you specify for any dependent assemblies.
• It forms a deployment unit. When an application starts, only the assemblies that the application initially calls must be present. Other assemblies, such as localization resources or assemblies containing utility classes, can be retrieved on demand. This allows applications to be kept simple and thin when first downloaded.
• It is the unit at which side-by-side execution is supported.
Assemblies can be static or dynamic. Static assemblies can include .NET Framework types (interfaces and classes), as well as resources for the assembly (bitmaps, JPEG files, resource files, and so on). Static assemblies are stored on disk in PE files. You can also use the .NET Framework to create dynamic assemblies, which are run directly from memory and are not saved to disk before execution. You can save dynamic assemblies to disk after they have executed.
There are several ways to create assemblies. You can use development tools, such as Visual Studio .NET, that you have used in the past to create .dll or .exe files. You can use tools provided in the .NET Framework SDK to create assemblies with modules created in other development environments. You can also use common language runtime APIs, such as Reflection.Emit, to create dynamic assemblies.
Versioning
Each assembly has a 128-bit version number that is presented as a set of four decimal pieces: Major.Minor.Build.Revision
For example, an assembly might have the version number 3.5.0.126.
By default, an assembly will only use types from the exact same assembly (name and version number) that it was built and tested with. That is, if you have an assembly that uses a type from version 1.0.0.2 of another assembly, it will (by default) not use the same type from version 1.0.0.4 of the other assembly. This use of both name and version to identify referenced assemblies helps avoid the "DLL Hell" problem of upgrades to one application breaking other applications.
Changes to which portion of version number indicates an incompatible change?
Major or minor. Changes to the major or minor portion of the version number indicate an incompatible change. Under this convention then, version 2.0.0.0 would be considered incompatible with version 1.0.0.0. Examples of an incompatible change would be a change to the types of some method parameters or the removal of a type or method altogether. Build. The Build number is typically used to distinguish between daily builds or smaller compatible releases. Revision. Changes to the revision number are typically reserved for an incremental build needed to fix a particular bug. You'll sometimes hear this referred to as the "emergency bug fix" number in that the revision is what is often changed when a fix to a specific bug is shipped to a customer.
What is side-by-side execution? Can two application one using private assembly and other using Shared assembly be stated as a side-by-side executables?
Side-by-side execution is the ability to run multiple versions of an application or component on the same computer. You can have multiple versions of the common language runtime, and multiple versions of applications and components that use a version of the runtime, on the same computer at the same time. Since versioning is only applied to shared assemblies, and not to private assemblies, two application one using private assembly and one using shared assembly cannot be stated as side-by-side
executables.
How do assemblies find each other?
By searching directory paths. There are several factors which can affect the path (such as the AppDomain host, and application configuration files), but for private assemblies the search path is normally the application's directory and its sub-directories. For shared assemblies, the search path is normally same as the private assembly path plus the shared assembly cache.
How does assembly versioning work?
Each assembly has a version number called the compatibility version. Also each reference to an assembly (from another assembly) includes both the name and version of the referenced assembly.The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed compatible. However, this is just the default guideline - it is the version policy that decides to what extent these rules are enforced. The version policy can be specified via the application configuration file.
What is an assembly?
An assembly is the primary building block of a .NET Framework application. It is a collection of functionality that is built, versioned, and deployed as a single implementation unit (as one o...
What is a Strong Name?
A strong name consists of the assembly's identity — its simple text name, version number, and culture information (if provided) — plus a public key and a digital signature. It is z
What are the contents of assembly?
In general, a static assembly can consist of four elements:
• The assembly manifest, which contains assembly metadata.
• Type metadata.
• Microsoft intermediate language (MSIL) code that implements the types.
• A set of resources.
Explain Manifest and Metadata?
Manifest: Manifest describes assembly itself.
Assembly Name, version number, culture, strong name, list of all files, Type references, and referenced assemblies.
Metadata: Metadata describes contents in an assembly classes, interfaces, enums, structs, etc., and their containing namespaces, the name of each type, its visibility/scope, its base class, the interfaces it implemented, its methods and their scope, and each method’s parameters, type’s properties, and so on.
What is difference between MetaData and Manifest ?
Metadata and Manifest forms an integral part of an assembly( dll / exe ) in .net framework .
Out of which Metadata is a mandatory component , which as the name suggests gives the details about various components of IL code viz : Methods , properties , fields , class etc.
Essentially Metadata maintains details in form of tables like Methods Metadata tables , Properties Metadata tables , which maintains the list of given type and other details like access specifier , return type etc.
Now Manifest is a part of metadata only , fully called as “manifest metadata tables” , it contains the details of the references needed by the assembly of any other external assembly / type , it could be a custom assembly or standard System namespace .
Now for an assembly that can independently exists and used in the .Net world both the things ( Metadata with Manifest ) are mandatory , so that it can be fully described assembly and can be ported anywhere without any system dependency . Essentially .Net framework can read all assembly related information from assembly itself at runtime .
But for .Net modules , that can’t be used independently , until they are being packaged as a part of an assembly , they don’t contain Manifest but their complete structure is defined by their respective metadata .
Ultimately . .Net modules use Manifest Metadata tables of parent assembly which contain them .
Difference between assembly manifest & metadata?
Assembly manifest - An integral part of every assembly that renders the assembly self-describing. The assembly manifest contains the assembly's metadata. The manifest establishes the assembly identity, specifies the files that make up the assembly implementation, specifies the types and resources that make up the assembly, itemizes the compile-time dependencies on other assemblies, and specifies the set of permissions required for the assembly to run properly. This information is used at run time to resolve references, enforce version binding policy, and validate the integrity of loaded assemblies. The self-describing nature of assemblies also helps makes zero-impact install and XCOPY deployment feasible.
metadata - Information that describes every element managed by the common language runtime: an assembly, loadable file, type, method, and so on. This can include information required for debugging and garbage collection, as well as security attributes, marshaling data, extended class and member definitions, version binding, and other information required by the runtime.
What is a Metadata?
Metadata is information about a PE. In COM, metadata is communicated through non-standardized type libraries. In .NET, this data is contained in the header portion of a COFF-compliant PE and ...
What is a Manifest?
An assembly manifest contains all the metadata needed to specify the assembly's version requirements and
security identity, and all metadata needed to define the scope of the assembly and res... '
What are the different types of assemblies?
Private, Public/Shared, Satellite
What is the difference between a private assembly and a shared assembly?
0. Location and visibility: A private assembly is normally used by a single application, and is stored in the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code which many applications will find useful, e.g. the .NET framework classes.
1. Versioning: The runtime enforces versioning constraints only on shared assemblies, not on private assemblies.
How’s the DLL Hell problem solved in .NET?
Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.
How does assembly versioning in .NET prevent DLL Hell?
.NET allows assemblies to specify the name AND the version of any assemblies they need to run.
What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
What’s a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies. An assembly containing localized resources for another assembly.
What are Satellite Assemblies? How you will create this? How will you get the different language strings?
Satellite assemblies are often used to deploy language-specific resources for an application. These language-specific assemblies work in side-by-side execution because the application has a separate product ID for each language and installs satellite assemblies in a language-specific subdirectory for each language. When uninstalling, the application removes only the satellite assemblies associated with a given language and .NET Framework version. No core .NET Framework files are removed unless the last language for that .NET Framework version is being removed.
(For example, English and Japanese editions of the .NET Framework version 1.1 share the same core files. The Japanese .NET Framework version 1.1 adds satellite assemblies with localized resources in a \ja subdirectory. An application that supports the .NET Framework version 1.1, regardless of its language, always uses the same core runtime files.)
http://www.ondotnet.com/lpt/a/2637
How will u load dynamic assembly? How will create assemblies at run time?
we should use the AppDomain.CreateInstanceAndUnwrap instead.
The difference between the two functions are just like the difference between Assembly.Load and Assembly.LoadFrom. Load will search the assembly obey the .net 's assembly locating rules. From GAC to private bin path...
But the LoadFrom instead, will not. It require the caller to provide a full
path of the assembly such as LoadFrom("c:\folder\test.dll") , if we don't provide a absolute full path,
it will use the current directory ("Environment.CurrentDirectory").
So as for our issue, we have to alternative means:
1. Use the AppDomain.CreateInstanceAndUnwrap instead of AppDomain.CreateInstanceFromAndUnwrap , that will make the runtime to locate the assembly in the privatebin path we specified in the appdomain's
setup info.
#note :
Another thing I'd like to point out is that the setup info's "PrivateBinPath" is not a absolute path, it should be a subfolder name which will be combined with the appdomain's basedirectory path so that generate the whole runtime search path, for example:
string appbase = string appbase = Server.MapPath("~/");
setup.ApplicationBase = appbase + "Addins";
setup.PrivateBinPath = "bin";
2. Still use the AppDomain.CreateInstanceFromAndUnwrap, but we should specify the full path of the assembly, for example:
util = (CSLib.CSUtil)appDomain.CreateInstanceFromAndUnwrap(appbase + "Addins\\bin\\"+"CSLib.dll", "CSLib.CSUtil");
Please have a look at the above suggestions. Hope they will help. Thanks.
What is Assembly manifest? what all details the assembly manifest will contain?
Every assembly, whether static or dynamic, contains a collection of data that describes how the elements in the assembly relate to each other. The assembly manifest contains this assembly metadata. An assembly manifest contains all the metadata needed to specify the assembly's version requirements and security identity, and all metadata needed to define the scope of the assembly and resolve references to resources and classes. The assembly manifest can be stored in either a PE file (an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a standalone PE file that contains only assembly manifest information.
It contains Assembly name, Version number, Culture, Strong name information, List of all files in the assembly, Type reference information, Information on referenced assemblies.
What are the differences between a .NET Assembly, a Windows DLL and a COM Component?
A Windows DLL contains library code to be used by any program running on Windows. A DLL may contain either structured or object oriented libraries.
COM (Component Object Model) is the component model based on the object oriented design, which means that the components represented by the COM component exists in the form of classes and objects implementing a standard specification defined by COM. COM components can be used by any program running on Windows Operating System; be it is written with VB, C++, Java or even some .NET compliant language like C# and VB.NET.
Dot NET assembly is the component standard specified by the .NET. Hence, dot net assemblies are understandable to only Microsoft.NET and can be used only in .NET managed applications.
If I have more than one version of one assemblies, then how'll I use old version (how/where to specify version number?)in my application?
**
How to find methods of a assembly file (not using ILDASM)
What is strong name?
A name that consists of an assembly's identity—its simple text name, version number, and culture information (if provided)—strengthened by a public key and a digital signature generated over the assembly. Because the assembly manifest
contains file hashes for all the files that constitute the assembly implementation, it is sufficient to generate the digital signature over just the one file in the assembly that contains the assembly manifest. Assemblies with the same strong name are expected to be identical
What is difference between shared and public?
An assembly that can be referenced by more than one application. An assembly must be explicitly built to be shared by giving it a cryptographically strong name.
Whats an assembly?
Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the context of an assembly.
What is namespace used for loading assemblies at run time and name the methods?
System.Reflection
What's a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.
How many classes can a single .NET DLL contain?
Unlimited.
What is manifest?
It is the metadata that describes the assemblies.
What is metadata?
Metadata is machine-readable information about a resource, or ""data about data."" Such information might include details on content, format, size, or other characteristics of a data
source. In .NET, metadata includes type definitions, version information, external assembly references, and other standardized information.
What are the types of assemblies?
There are four types of assemblies in .NET:
Static assemblies
These are the .NET PE files that you create at compile time.
Dynamic assemblies
These are PE-formatted, in-memory assemblies that you dynamically create at runtime using the classes in the System.Reflection.Emit namespace.
Private assemblies
These are static assemblies used by a specific application.
Public or shared assemblies
These are static assemblies that must have a unique shared name and can be used by any application.
An application uses a private assembly by referring to the assembly using a static path or through an XML-based application configuration file. While the CLR doesn't enforce versioning policies-checking whether the correct version is used-for private assemblies, it ensures that an
application uses the correct shared assemblies with which the application was built. Thus, an application uses a specific shared assembly by referring to the specific shared assembly, and the CLR ensures that the correct version is loaded at runtime.
In .NET, an assembly is the smallest unit to which you can associate a version number;
Can I look at the IL for an assembly?
Yes. MS supply a tool called Ildasm which can be used to view the metadata and IL for an assembly.
Can source code be reverse-engineered from IL?
Yes, it is often relatively straightforward to regenerate high-level source (e.g. C#) from IL.
How can I stop my code being reverse-engineered from IL?
There is currently no simple way to stop code being reverse-engineered from IL. In future it is likely that IL obfuscation tools will become available, either from MS or from third parties. These tools work by 'optimising' the IL in such a way that reverse-engineering becomes much more difficult.
Of course if you are writing web services then reverse-engineering is not a problem as clients do not have access to your IL.
How many classes can a single .NET DLL contain?
Unlimited.
How many .NET languages can a single .NET DLL contain?
One
What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
What is manifest?
It is the metadata that describes the assemblies.
What is metadata?
Metadata is machine-readable information about a resource, or ""data about data."" Such information might include details on content, format, size, or other characteristics of a data source. In .NET, metadata includes type definitions, version information, external assembly references, and other standardized information.
What are the types of assemblies?
There are four types of assemblies in .NET:
Static assemblies
These are the .NET PE files that you create at compile time.
Dynamic assemblies
These are PE-formatted, in-memory assemblies that you dynamically create at runtime using the classes in the System.Reflection.Emit namespace.
Private assemblies
These are static assemblies used by a specific application.
Public or shared assemblies
These are static assemblies that must have a unique shared name and can be used by any application.
An application uses a private assembly by referring to the assembly using a static path or through an XML-based application configuration file. While the CLR doesn't enforce versioning policies-checking whether the correct version is used-for private assemblies, it ensures that an
application uses the correct shared assemblies with which the application was built. Thus, an application uses a specific shared assembly by referring to the specific shared assembly, and the CLR ensures that the correct version is loaded at runtime.
In .NET, an assembly is the smallest unit to which you can associate a version number;
What is an Asssembly Qualified Name? Is it a filename? How is it different?
An assembly qualified name isn't the filename of the assembly; it's the internal name of the assembly combined with the assembly version, culture, and public key, thus making it unique.
e.g. (""System.Xml.XmlDocument, System.Xml, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"")
How is a strongly-named assembly different from one that isn’t strongly-named?
Strong names are used to enable the stricter naming requirements associated with shared assemblies. These strong names are created by a .NET utility – sn.exe
Strong names have three goals:
· Name uniqueness. Shared assemblies must have names that are globally unique.
· Prevent name spoofing. Developers don't want someone else releasing a subsequent version of one of your assemblies and falsely claim it came from you, either by accident or intentionally.
· Provide identity on reference. When resolving a reference to an assembly, strong names are used to guarantee the assembly that is loaded came from the expected publisher.
Strong names are implemented using standard public key cryptography. In general, the process works as follows: The author of an assembly generates a key pair (or uses an existing one), signs the file containing the manifest with the private key, and makes the public key available to callers. When references are made to the assembly, the caller records the public key corresponding to the private key used to generate the strong name.
Weak named assemblies are not suitable to be added in GAC and shared. It is essential for an assembly to be strong named.
Strong naming prevents tampering and enables assemblies to be placed in the GAC alongside other assemblies of the same name.
How do you create shared assemblies?.
Just look through the definition of Assemblies..
* An Assembly is a logical unit of code
* Assembly physically exist as DLLs or EXEs
* One assembly can contain one or more files
* The constituent files can include any file types like image files, text files etc. along with DLLs or EXEs
* When you compile your source code by default the exe/dll generated is actually an assembly
* Unless your code is bundled as assembly it can not be used in any other application
* When you talk about version of a component you are actually talking about version of the assembly to which the component belongs.
* Every assembly file contains information about itself. This information is called as Assembly Manifest.
Following steps are involved in creating shared assemblies :
* Create your DLL/EXE source code
* Generate unique assembly name using SN utility
* Sign your DLL/EXE with the private key by modifying AssemblyInfo file
* Compile your DLL/EXE
* Place the resultant DLL/EXE in global assembly cache using AL utility
What is the difference between an executable assembly and a class library?
An executable assembly exists as the .exe file while a class library exists as the .dll file. Executable assembly represent executable applications having some entry (e.g., Main() method in C#). A class library, on the other hand, contains components and libraries to be used inside various applications. A Class library can not be executed and thus it does not have any entry point.
How do I unload an assembly?
CLR does not provide a way to unload an assembly. The only mechanism to remove the assembly is to unload the application domain in which the assembly is loaded. If you wish to remove an assembly after it has been used, you should create an application domain, load the assembly into the created application domain, and then unload the application domain when you no longer need the assembly.
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