While using triggers these Inserted & Deleted tables
(called as magic tables) will be created automatically.
When we insert any record then that record will be added
into this Inserted table initially, similarly while
updating a record a new entry will be inserted into
Inserted table & old value will be inserted into Deleted
table.
In the case of deletion of a record then it will insert
that record in the Deleted table
A
variation of the multidimensional array is the jagged array: an array of
arrays. A jagged array is a single-dimensional array, and each element is
itself an array. The element arrays are not required to all be of the same
size.
You
declare a jagged array like this:
int[][] jaggedArray = new int[3][];
Doing
so creates an array of three arrays. These arrays can be initialized like this:
Arraylist accept values as object
So We can give any type of data in to that.
Here in this eg: an arraylist object accepting
values like String,int,decimal, char and a custom object
ArrayList arr = new ArrayList();
arr.Add("Sabu");
arr.Add(234);
arr.Add(45.236);
arr.Add(emp);
arr.Add('s');
This process is known as boxing
Geniric
Main advantage of Generic List is we can specify the type of data
List<int> intLst = new List<int>();
intLst.Add(12);
Here List accepting values as int only
List<Employee> empLst = new List<Employee>();
empLst.Add(new Employee("1", "Sabu"));
Here List accepting Employee Objects only
If constructor is private then we can not create the object and inherit of that
class.
-> Sealed can not be used for virtual, Abstract and static classes.
Non - Generic collection class - which collection can hold
the different type of data. Generic collection class - which collection can hold the
same type of data.
cookies
are small bits of files that store your session, and other small data, its
pretty much like a database in a sense...
while
a cache is temporary storage for files used by a program(typically a browser)
to display items.... and to get a quick access to pre-parsed files.....
your browser has to store the webpage, and all pictures, video flash and those
things on the cache so that it could display it
while cookies, store only text based data about your browsing stuff.. like
passwords, number of pages visited, session number, and so on
Memory management is the main concern for any application whether
application is window based or web based. In .Net, CLR has garbage
collector that executes as a part of our program and responsible for
reclaiming the memory of no longer used objects. Garbage collector free
the memory for objects that are no longer referenced and keeps the
memory for future allocations.
Advantage of Garbage Collector
Allow us to develop an application without having worry to free memory.
Allocates memory for objects efficiently on the managed heap.
-Reclaims the memory for no longer used objects and keeps the free memory for future allocations.
Provides memory safety by making sure that an object cannot use the content of another object.
Memory Allocation in Managed Heap
The managed heap is a series of allocated memory segments (approx 16Mb
in size each) to store and manage objects. The memory for newly created
object is allocated at the next available location on the managed heap.
If there is available free memory, the garbage collector doesn't search
the dead objects for memory reclaim and memory allocations has been
done very fast. If the memory is insufficient to create the object, the
garbage collector search the dead objects for memory reclaim for the
newly object.
An object is created using the new operator. This operator first makes
sure that the bytes required by the new object fit in the reserved
region (committing storage if necessary). If the object fits, NextObjPtr points to the object in the heap and object's constructor is called and the new operator returns the address of the object.
Impotants points
All objects in the heap are allocated from one contiguous range of
memory address and heap is divided into generations so that it is easy
to eliminate the garbage objects by looking at only a small fraction of
the heap.
Gen 0 and Gen 1 occupy a single segment known as the ephemeral
segment. Gen 2 is a set of further segments and the large object heap
is yet another group of segments.
Almost, all objects with-in a generation are of the same age.
The newest objects are created at higher memory address while
oldest memory objects are at lowest memory address with in the heap.
The allocation pointer for the new objects marks the boundary between the allocated and free memory.
Periodically the heap is compacted by removing the dead objects
and sliding up the live objects towards the lower memory address end of
the heap as shown in above fig.
The order of objects (after memory reclaims) in memory remains the same as they were created.
There are never any gaps among the objects in the heap.
Only some of the free memory is committed when required and more
memory is acquired from the OS in the reserved address range.
Generations in Managed Heap
The managed heap is organized into three generations so that it can
handle short lived and long lived objects efficiently. Garbage
collector first reclaim the short lived objects that occupy a small
part of the heap.
Generation 0
This is the youngest generation and contains the newly created objects.
Generation 0 has short-lived objects and collected frequently. The
objects that survive the Generation 0 are promoted to Generation 1. Example : A temporary object.
Generation 1
This generation contains the longer lived objects that are promoted
from generation 0. The objects that survive the Generation 1 are
promoted to Generationen 2. Basically this generation serves as a
buffer between short-lived objects and longest-lived objects.
Generation 2
This generation contains the longest lived objects that are promoted from generation 1 and collected infrequently. Example : An object at application level that contains static data which is available for the duration of the process.
Garbage Collector Working Phase
Marking Phase
In this phase garbage collector finds and creates a list of all live objects.
Relocating Phase
In this phase garbage collector updates the references to the objects that will be compacted.
Compacting Phase
In this phase garbage collector reclaims the memory occupied by the
dead objects and compacts the surviving objects. The compacting phase
moves the surviving objects toward the older end of the memory segment.
The Page_Init event is the first event to be triggered in the page life
cycle. In this the control tree has been created, the controls declared in the .aspx
file are initialized. The viewstate is not available at this stage. We can create
or re-create the controls that need to be created or re-created dynamically.
LoadViewState
The Viewstate contains stored information that is set by the page and controls
of the page. But the load view state event only occurs when the page has been posted
back. Due to viewstate control's and page itself store information that is persistent
among web requests. It contains the state of the controls the last time the page
was processed on the server.
LoadPostData
After viewstate is loaded the control
are updated with posted values or values that are entered or changed by user.
Page_Load
After Loadpostdata the page_load event is fired. In this event code written inside
page load is executed once at the beginning of the page.
RaisePostDataChangedEvent
In this event when user clicks submit button or any other button then it changes
state of the page and the event related to that button is raised.
RaisePostBackEvent
This methods knows which event has occurred and which related method you need to
call like btnsubmit is clicked then it will call method related to it like “btnsubmit_click”
to perform its functionality.
Page_PreRender
At this stage page is prepared for
Rendering and if user wants to chage anything he can change it here only as in this
event viewstate is not saved and output is not rendered.
SaveViewState
In this
event values of viewstate is saved to control own viewstate collection. The resultant
viewstate is serialized, hashed, base24 encoded and associated with the _viewstate
hidden field.
Page_Render
This method takes the HtmlWriter object and uses it
to accumulate all HTML text to be generated for the control. For each control the
page calls the render method and caches the HTML output.
Page_unload
During this method, data can be released to free up resources on the server for
other processes. Once this method is completed, the HTML is sent to the browser
for client side processing.
What are the different levels of State
management in ASP.NET?
State management is the process by
which you maintain state and page information over multiple requests for the
same or different pages.
There are 2 types State Management: 1.Client – Side State Management 2.Server – Side State Management 1. Client – Side State Management
This stores information on the client's computer by embedding the information
into a Web page, a uniform resource locator (url), or a cookie. The techniques
available to store the state information at the client end are listed down
below:
a. View State – Asp.Net uses View State to track the values in the Controls.
You can add custom values to the view state. It is used by the Asp.net page
framework to automatically save the values of the page and of each control just
prior to rendering to the page. When the page is posted, one of the first tasks
performed by page processing is to restore view state.
b. Control State – If you create a custom control that requires view state to
work properly, you should use control state to ensure other developers don’t
break your control by disabling view state.
c. Hidden fields – Like view state, hidden fields store data in an HTML form
without displaying it in the user's browser. The data is available only when
the form is processed.
d. Cookies – Cookies store a value in the user's browser that the browser sends
with every page request to the same server. Cookies are the best way to store
state data that must be available for multiple Web pages on a web site.
e. Query Strings - Query strings store values in the URL that are visible to
the user. Use query strings when you want a user to be able to e-mail or
instant message state data with a URL.
2. Server – Side State Management a. Application State - Application State information is available to all pages,
regardless of which user requests a page.
b. Session State – Session State information is available to all pages opened
by a user during a single visit.
Both application state and session state information is lost when the
application restarts. To persist user data between application restarts, you
can store it using profile properties.
