How to check if Silverlight Running out of browser or in the browser ?

As Silverlight increases its Out of Browser features it will become more important to detect if the application is running in or out of the browser.  This is the check:

if (Application.Current.IsRunningOutOfBrowser)
{
       // Out of Browser 

}
else

{
      //   in the browser

}

How to open Excel XLS file in C#.net

Suppose you have an excel file that contains the data and you wish to use the same The following code snippet will read the file and return it in a dataset now you are free to use this dataset for your purpose.

static DataSet readExcel()
{
string filename = "";
string sheetname = "";
filename = "";
sheetname = "";
OleDbConnection con = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + filename + ";Extended Properties=Excel 8.0");
con.Open();
DataSet myDataSet = new DataSet();
OleDbDataAdapter myCommand = new OleDbDataAdapter(" SELECT * FROM ["+sheetname+"$]", con);
myCommand.Fill(myDataSet);
con.Close();
return myDataSet;
}

Error: ASPX page has not been pre-compiled, and cannot be requested

Sometime we find that our web site was working perfectly on our development machine but start displaying error “ Error: ASPX page has not been pre-compiled, and cannot be requested” in many of forums I foud many of our peers are still struggling with same issue.

The simple workaround for that I have found is :

1. If you are using any 3rd party component , remove them from web.config, then using Add Reference add all reference to them again.
2. Instead of setting the WDP's Output Assemblies property to “Merge all outputs to a single assembly” and deploy, use Publish Web Site under the Build menu.
3. Check the "Allow this precompiled site to be updatable" check box in the Publish Web Site options of Visual Studio 05, and deploy.
4. make sure you uploaded all the required assemblies. If anyone is missing upload that manually.

Hope this information will be helpful to my peer community.

General network error. Check your network documentation.

There is a lot of people out there complaining about SQL Server returning a General network error while executing a command form ADO.NET version 1.1 or 1.0. Since it is a General network error, it seems to me that there are as many reasons for this error as there are people having it. one fine day I too experienced the same so I googled it but saveral posts in several blogs leads to various solutions like append max pool size = 7500, to your connection string will solve the issue or setting the command timeout to anything but zero totally fixes it.

I tried all of them but still i experienced the same error intermittently. Finally i found that The calling asp.net page creates an ojbect which opens the connection over and over and relies on the destruct method of the database object to do the closing so I am assuming our problem is related to this but I have not been able to reproduce it reliably so I can't be sure this is the cause of the problem.

then i found this microsoft KB article

it says that In the current design, after an application role is enabled on a client connection to SQL Server, you cannot reset the security context of that connection. Therefore, when the user ends the SQL Server session and disconnects from the server, the session is not reusable. However, OLE DB resource pooling returns the closed connection to the pool, and the error occurs when that connection is reused and the client application tries to reset the connection's security context by calling sp_setapprole again.

WORKAROUND

The only available workaround is to disable OLE DB Resource Pooling, which ADO uses by default. You can do this by adding "OLE DB Services = -2" to the ADO Connection string, as shown here: 'For SQLOLEDB provider
'strConnect = "Provider=SQLOLEDB;server=SQL7Web;OLE DB Services = -2;uid=AppUser;pwd=AppUser;initial catalog=northwind"

' For MSDASQL provider
'strConnect = "DSN=SQLNWind;UID=Test;PWD=Test; OLE DB Services= -2"


Pooling can be disabled for the SQL Server .Net Data Provider by adding "Pooling=False" to the connection string.

although that solves my issue but what if the connection pooling is needed ????

What is equivalent for regsvr32 exe in .NET?

Regasm

What are types of compatibility inVB6?

There are three possible project compatibility settings: - No compatibility - Project compatibility - Binary compatibility No Compatibility With this setting, new class ID’s, new interface ID’s and a new type library ID will be generated by VB each time the ActiveX component project is compiled. This will cause any compiled client components to fail(with error 429!) and report a missing reference to the `VB ActiveX Test component’ when a client project is loaded in the VB IDE. Note: Use this setting to compile the initial release of a component to other developers. Project Compatibility With this setting, VB will generate new interface ID’s for classes whose interfaces have changed, but will not change the class ID’s or the type library ID. This will still cause any compiled client components to fail(with error 429!)but will not report a missing reference to the `VB ActiveX Test component’ when a client project is loaded in the VB IDE. Recompilation of client components will restore them to working order again. Note: Use this setting during the initial development and testing of a component within the IDE and before the component is released to other developers. Binary Compatibility VB makes it possible to extend an existing class or interface by adding new methods and properties etc. And yet still retain binary compatibility. It can do this, because it silently creates a new interface ID for the extended interface and adds registration code to register the original interface ID but with a new forward key containing the value of the new interface ID.COM will then substitute calls having the old ID with the new ID and hence applications built against the old interface will continue to work(assuming the inner workings of the component remain backward compatible!). With this settings, VB will not change any of the existing class, interface or type library ID’s, however in order that it can do so, VB requires the project to specify an existing compiled version that it can compare against to ensure that existing interfaces have not been broken.

How do you do object pooling in .NET?

COM+ reduces overhead by creating object from scratch. So in COM+ when object is activated from its pool and when it’s deactivated it’s pushed back to the pool. Objects pooling is configured by using the “ObjectPoolingAttribute” to the class.

How to implement DTC in .NET?

DTC is implemented using COM+. Following are the steps to implement COM+ in .NET: - “EnterpriseService” namespace has all the classes by which we can implement DTC in .NET. You have to add reference “EnterpriseService” namespace. - Your class must derive from “Service Component” object. - Then you have to define your class with the transaction attribute - After the class level transaction type is defined, its time to define at the method level the AutoComplete attribute. AutoComplete attribute says that if no exception is thrown then mark its part of the transaction as being okay. This helps cut down on the amount of code required. If the implementation sets AutoComplete to false, or omits it all together, then we would need to manage the transaction manually. To manually control the transaction you will need to use the ContextUtil class and its static members.

How do we create DCOM objects in VB6?

Using the Create Object method you can create a DCOM object. You have to put the server name in the registry.

Can you describe IUKNOWN interface in short?

Every COM object supports at least one interface, the IUnknown interface. All interfaces are classes derived from the base class IUnknown. Each interface supports methods access data and performs operations transparently to the programmer. For example, IUnknown supports three methods, AddRef, Release (), and QueryInterface(). Suppose that printerf is a pointer to an IUnknown. Printerf->;AddRef() increments the reference count. Printerf->;Release() decrements the reference count, deleting the object when the reference count reaches zero. Printerf->;QueryInterface(IDesired, pDesired) checks to see if the current interface (IUnknown) supports snother interface, IDesired, creates an instance (via a call to CoCreateInstance()) of the object if the reference count is zero (the object does not yet exist), and then calls pDesired->;AddRef() to increment the reference count (where pDesired is a pointer to IDesired) and returns the pointer to the caller.

What is Reference counting in COM?

Reference counting is a memory management technique used to count how many times an object has a pointer referring to it. The first time is it created; the reference count is set to one. When the last reference to the object is nulled, the reference count is set to zero and the object is deleted. Care must be exercised to prevent a context switch from changing the reference count at the time of deletion.

How can we use .NET components in COM?Twist: What is CCW (COM callable wrapper)? Twist: How do we ensure that .NET component is compatible with COM?

.NET components can not be used in straight forward way with COM. You will need to create CCW in order that COM components communicate with .NET assemblies. Other way to create CCW is by using InteropServices attributes. Here interfaces are created automatically. Following are different types of attributes: -None: No class interface is generated for the class. This is default setting when you do not specify anything. -AutoDispatch: Interface that supports IDispatch is created for the class. However, no type information is produced. -AutoDual: A dual interface is created for the class. Type information is produced and made available in the type library. Below in the source code we have used the third attribute. Imports System.Runtime.InteropServices _ Public Class ClsCompliant End Class Other than class attributes defined up there are other attributes with which you can govern other part of assembly. Example “GuidAttribute” allows you to specify the GUID, “ComVisibleAttribute” can be used to hide .NET types from COM etc. -Once .NET assembly is created using either interface or using Interopservices method we need to create a COM type library using Type library export tool [Tlbexp (AssemblyName)] -The final thing is registering the CCW in registry using regasm tool. Regasm AssemblyName[Options] and that's it.

How can we use COM Components in .NET? Twist: What is RCW?

Dot NET components communicate with COM using RCW (Runtime Callable Wrapper). Following are the ways with which you can generate RCW: -Adding reference in Visual Studio.net -Using Type library import tool. Tlbimp.exe yourname.dll -Using interopservices.System.runtime. Interopservices namespace contains class TypeLib Converter which provides methods to convert COM classes and interface in to assembly metadata. -Make your custom wrappers. If your COM component does not have type library then the only way to communicate is writing custom wrappers. That means communicating directly with COM components.

What is CODE Access security?

To help protect computer systems from malicious mobile code, to allow code from unknown origins to run with protection, and to help prevent trusted code from intentionally or accidentally compromising security, the .NET Framework provides a security mechanism called code access security. Code access security allows code to be trusted to varying degrees depending on where the code originates and on other aspects of the code's identity. Code access security also enforces the varying levels of trust on code, which minimizes the amount of code that must be fully trusted in order to run. Using code access security can reduce the likelihood that your code can be misused by malicious or error-filled code. It can reduce your liability because you can specify the set of operations your code should be allowed to perform as well as the operations your code should never be allowed to perform. Code access security can also help minimize the damage that can result from security vulnerabilities in your code.

All managed code that targets the common language runtime receives the benefits of code access security, even if that code does not make a single code access security call.

What'is difference between System exceptions and Application exceptions?

From the System.SystemException documentation:

This class is provided as a means to differentiate between exceptions defined by the system versus exceptions defined by applications.

So, consider it the opposite of ApplicationException. All Exceptions that are defined by the .NET Framework inherit from SystemException. All Exceptions that are defined by code that you write should derive from ApplicationException. Exception is the root class of ALL exceptions.

What is the difference between VB.NET and C# ?

Well this is the most debatable issue in .NET community and people treat these languages like religion. It’s a subjective matter which language is best. Some like VB.NET’s natural style and some like professional and terse C# syntaxes. Both use the same framework and speed is also very much equivalents.
But still let’s list down some major differences between them
:-Advantages VB.NET :-Has support for optional parameters which makes COM interoperability much easy. With Option Strict off late binding is supported. Legacy VB functionalities can be used by using Microsoft.VisualBasic namespace. Has the WITH construct which is not in C#. The VB.NET part of Visual Studio .NET compiles your code in the background. While this is considered an advantage for small projects, people creating very large projects have found that the IDE slows down considerably as the project gets larger. Advantages of C# XML documentation is generated from source code but this is now been incorporated in Whidbey. Operator overloading which is not in current VB.NET but is been introduced in Whidbey. Use of this statement makes unmanaged resource disposal simple. Access to Unsafe code. This allows pointer arithmetic etc, and can improve performance in some situations. However, it is not to be used lightly, as a lot of the normal safety of C# is lost (as the name implies).
This is the major difference that you can access unmanaged code in C# and not in VB.NET.

What is concept of Boxing and Unboxing ?

Boxing permits any value type to be implicitly converted to type object or to any interface type implemented by value type. Boxing is a process in which object instances are created and copy values in to that instance. Unboxing is vice versa of boxing operation where the value is copied from the instance in to appropriate storage location. Below is sample code of boxing and unboxing where integer data type is converted in to object and then vice versa.

Dim x As IntegerDim y As Object x = 10‘ boxing process y = x‘ unboxing process x = y

What are Value types and Reference types ?

Value types directly contain their data which are either allocated on the stack or allocated in-line in a structure. Reference types store a reference to the value's memory address, and are allocated on the heap. Reference types can be self-describing types, pointer types, or interface types. Variables that are value types each have their own copy of the data, and therefore operations on one variable do not affect other variables. Variables that are reference types can refer to the same object; therefore, operations on one variable can affect the same object referred to by another variable. All types are derived from the System.Object base type.

What are different types of JIT ?

JIT compiler is a part of the runtime execution environment. In Microsoft .NET there are three types of JIT compilers

1)Pre-JIT :- Pre-JIT compiles complete source code into native code in a single compilation cycle. This is done at the time of deployment of the application.

2)Econo-JIT :- Econo-JIT compiles only those methods that are called at runtime. However, these compiled methods are removed when they are not required.

3)Normal-JIT :- Normal-JIT compiles only those methods that are called at runtime. These methods are compiled the first time they are called, and then they are stored in cache. When the same methods are called again, the compiled code from cache issued for execution.

What is reflection?

All .NET assemblies have metadata information stored about the types defined in modules. This metadata information can be accessed by mechanism called as “Reflection”. System. Reflection can be used to browse through the metadata information. Using reflection you can also dynamically invoke methods using System.Type.Invokemember.