Imports System Public Class MainClass Shared Sub Main(ByVal args As String) Dim circle1, circle2 As Circle circle1 = New Circle(72, 29, 4.5) ' instantiate objects circle2 = New Circle(5, 5, 10) circle1 = Nothing ' mark objects for garbage collection circle2 = Nothing System.GC.Collect ' request garbage collector to execute End Sub End Class. To provide a sound knowledge about Object Oriented Programming in VB.NET. To educate how Object Oriented techniques are used in VB.NET. To explain the following concepts in an easy and simple way. Overrides Protected Sub Finalize Console.Writeline.
I have a class in which I have declared a FileStream and a StreamReader:
Option Strict Off Option Explicit On
I would like ask if I explicitely need to close these like this:
... or if that is done automatically.
Thank you for the help!
ps: I can not use 'using' because I want to read the file line by line like this:
I would suggest you use the same fonctionality as found in the stream. Implement the IDisposable interface and call .Dispose on your class instance when you're done with it. Same as you would do with a stream.
Here's a quick example.
NullReference Error while assiging values of Modeltype in MVC View (Razor)
vb.net,razor,model-view-controller,model
You need to pass the model instance to the view: Function Details() As ActionResult Dim employee As Employee employee = New Employee employee.EmployeeID = 101 Return View(employee) End Function ...
Laravel5: Access public variable in another class
php,class,oop,laravel,laravel-5
That's simple php stuff. Set the attribute as static and access it with ::. class LanguageMiddleware { public static $languages = ['en','es','fr','de','pt','pl','zh','ja']; } @foreach (AppHttpMiddlewareLanguageMiddleware::$languages as $lang) ... @endforeach You should not have that in a middleware though. You'd better add a configuration (i.e in /config/app.php) with that array, and...
Return index of word in string
arrays,vb.net,vbscript
Looking at your desired output it seems you want to get the index of word in your string. You can do this by splitting the string to array and then finding the item in an array using method Array.FindIndex: Dim animals = 'cat, dog, bird' ' Split string to array...
VBMath using / equivalent in C# [closed]
c#,vb.net
You need to add Microsoft.VisualBasic as a reference to your Project. In your Project in the Solution Explorer right-click References and select 'Add Reference'. Search for 'Microsoft.VisualBasic' in the Framework Tab.
Removing Alert When Using DeleteFile API
vb.net,vba,api,delete
There are several SHFILEOPSTRUCT.fFlags options you'll want to consider. You are asking for FOF_NOCONFIRMATION, &H10. You probably want some more, like FOF_ALLOWUNDO, FOF_SILENT, FOF_NOERRORUI, it isn't clear from the question. Check the docs.
Database only adds (x) amount of rows before error system resources exceeded
database,vb.net,ms-access
You should change your code to something like the following. Note that Everything that returns an object like OleDbConnection, OleDbCommand, or OleDbDataReader is wrapped in a Using block. These objects all implement the IDisposable interface, which means they should be cleaned up as soon as you're done with them. Also...
Invoke form showdialog is not modal
vb.net,multithreading,invoke
in the showDialog, you can set the parent form which causes the child to become modal: Public Class MainForm Dim frm2 As Form2 Private Sub MainForm_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load frm2 = New Form2() Dim frmHandle As IntPtr = frm2.Handle frm2.Button1.Text = 'test' System.Threading.ThreadPool.QueueUserWorkItem(New System.Threading.WaitCallback(AddressOf DoSomething), 0)...
How to pass all value of ListBox Control to a function?
vb.net,listbox
You're passing the contents of a ListBox to a method that is just displaying them in a MsgBox(). There are two approaches you can do to accomplish what I think you're wanting. You can pass ListBox.Items to the method and iterate through each item concatenating them into a single String...
Generic Interface missing implementation
vb.net,interface,implements,generic-interface
You need to indicate on the declaration of the Number function that it is the implementation of the Number Function defined in the Interface Interface IBuilder(Of T) Function Number(ByVal literal As String) As T End Interface Class BracketsBuilder Implements IBuilder(Of String) Public Function Number(number__1 As String) As String Implements IBuilder(Of...
ZipEntry() and converting persian filenames
vb.net,persian,sharpziplib
Try setting IsUnicodeText to true: 'VB.NET Dim newEntry = New ZipEntry(entryName) With { _ Key .DateTime = DateTime.Now, _ Key .Size = size, _ Key .IsUnicodeText = True _ } //C# var newEntry = new ZipEntry(entryName) { DateTime = DateTime.Now, Size = size, IsUnicodeText = true }; ...
Comparing arrays with numbers in vb.net
arrays,vb.net
There are a few basic ways of checking for a value in an integer array. The first is to manually search by looping through each value in the array, which may be what you want if you need to do complicated comparisons. Second is the .Contains() method. It is simpler...
ToInt32() conversion [on hold]
c#,class
The override keyword allows you to replace or extend the definition of a method in the base class that is marked with virtual. Since you haven't specified your base class explicitly, your object extends System.Object which does not define a ToInt32() method. Simply remove the override keyword and your class...
Connecting to database using Windows Athentication
sql-server,vb.net,authentication,connection-string
You need to add Integrated Security=SSPI and remove username and password from the connection string. Dim ConnectionString As String = 'Data Source=Server;Initial Catalog=m2mdata02;Integrated Security=SSPI;' ...
Custom drawing using System.Windows.Forms.BorderStyle?
c#,.net,vb.net,winforms,custom-controls
If you want to get results that reliably look like the BorderStyles on the machine you should make use of the methods of the ControlPaint object. For testing let's do it ouside of a Paint event: Panel somePanel = panel1; using (Graphics G = somePanel.CreateGraphics()) { G.FillRectangle(SystemBrushes.Window, new Rectangle(11, 11,...
How do I prevent MySQL Database Injection Attacks using vb.net?
mysql,.net,database,vb.net,sql-injection
MySQLCon.Open() Dim SQLADD As String = 'INSERT INTO members(member,gamertag,role) VALUES(@memberToAdd, @memberGamingTag, @memberRole)' COMMAND = New MySqlCommand(SQLADD, MySQLCon) COMMAND.Parameters.AddWithValue('@memberToAdd', memberToAdd.Text) COMMAND.Parameters.AddWithValue('@memberGamingTag', membersGamertag.Text) COMMAND.Parameters.AddWithValue('@memberRole', membersRole.Text) COMMAND.ExecuteNonQuery() memberToAdd.Text = ' membersGamertag.Text = ' membersRole.Text = ' MySQLCon.Close() MySQLCon.Dispose() You don't need to use...
check if a list contains all the element in an array using linq
vb.net,linq
You can use Enumerable.All: dim linqMeddata = From m In medicineDataList Where keys.All(Function(k) m.MedicineData.Contains(k)) Order By m.MedicineName Ascending Select m ...
Silex namespace : class MainController does not exist
php,class,namespaces,autoload,silex
I believe your problem is caused by the way you named your directory controllers. According to the documentation about PSR-4 standard: 5) Alphabetic characters in the fully qualified class name MAY be any combination of lower case and upper case. 6) All class names MUST be referenced in a case-sensitive...
Gridview items not populating correctly
asp.net,vb.net
Try this vb code behind, then comment out my test Private Sub BindGrid() Dim dt_SQL_Results As New DataTable ' Commenting out to use test data as I have no access to your database 'Dim da As SqlClient.SqlDataAdapter 'Dim strSQL2 As String 'Dim Response As String = ' 'strSQL2 = 'SELECT...
WPF style info from external text file
wpf,vb.net,styles
just hold the color values in a config file simple text file will suffice. though you can use VisualStudio Resource file.. file will contain lines in each: item_enum_name item_type item_value for example: main_screen_bg_color Color Black company_logo URI logoslogo1.jpg and so on.. just load the file parse it and use bind...
how can i use parameters to avoid sql attacks
sql,vb.net
I think the only solution is create a new function and gradually migrate to it. Public Function ExecuteQueryReturnDS(ByVal cmdQuery As SqlCommand) As DataSet Try Dim ds As New DataSet Using sqlCon As New SqlConnection(connStr) cmdQuery.Connection = sqlCon Dim sqlAda As New SqlDataAdapter(cmdQuery) sqlAda.Fill(ds) End Using Return ds Catch ex As...
.NET use IIF to assign value to different variables
.net,vb.net,conditional,variable-assignment,iif
What you're asking to do would have been possible in a language that supports pointer types (such as C/C++, or C# in unsafe mode) with dereferencing; VB.NET doesn't do that. The best you got to leverage is local variables, reference types, and (perhaps) ByRef. If it's a Class, its instantiation...
Retrieve full path of FTP file on drag & drop?
vb.net,ftp
If the data dropped contains a UniformResourceLocator format, you can get the entire URL from that, for example: Private Sub Form1_DragDrop(sender As Object, e As System.Windows.Forms.DragEventArgs) Handles Me.DragDrop If e.Data.GetDataPresent('UniformResourceLocator') Then Dim URL As String = New IO.StreamReader(CType(e.Data.GetData('UniformResourceLocator'), IO.MemoryStream)).ReadToEnd End If End Sub It first checks to see if a...
Call known function (with parameters) in class whose name is defined by string variable
java,function,class,variables
Your can use Reflection Object action = ???; // perhaps you need .newInstance() for action class // Hopefully you have a interface with performLogic String methodName = 'performLogic'; try { Method method = action.getClass().getMethod(methodName, param1.class, param2.class); method.invoke(action, param1, param2); } catch (SecurityException | NoSuchMethodException e) { // Error by get...
Set Label From Thread
vb.net,multithreading,winforms
The reason is that you are referring to the default instance in your second code snippet. Default instances are thread-specific so that second code snippet will create a new instance of the Form1 type rather then use the existing instance. Your Class1 needs a reference to the original instance of...
Convert Double from String
asp.net,vb.net,visual-studio-2012,converter
The result isn't wrong, it only has lower precision than you expected. Floating point numbers have a limited precision by design, and you simply can't expect to get a result that is more precise than its limit. You can use a Decimal to get higher precision. In this case it...
Get XML node value when previous node value conditions are true (without looping)
xml,vb.net,linq-to-xml
UPDATE Using an XDocument vs an XmlDocument, I believe this does what you're asking without using loops. This is dependent on the elements being in the order of <PhoneType> <PhonePrimaryYN> <PhoneNumber> string xml = '<?xml version='1.0'?>' + '<Root>' + ' <PhoneType dataType='string'>' + ' <Value>CELL</Value>' + ' </PhoneType>' + '...
Regex to check if string is alphanumeric separated by commas or a single alphanumeric string
regex,vb.net
^d{1,2}[A-Z]?(?:,d{1,2}[A-Z]?)*$ Try this.See demo. https://regex101.com/r/hI0qP0/25...
Scraping Javascript webpage (script error occurred)
javascript,html,vb.net,web,scrape
You can use WebBrowser.ScriptErrorsSuppressed = true; property. Details: https://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser.scripterrorssuppressed%28v=vs.110%29.aspx...
VB.Net DateTime conversion
jquery,vb.net,datetime
System.Globalization.DateTimeFormatInfo.InvariantInfo doesn't contain format pattern dd-MM-yyyy(26-06-2015) From MSDN about InvariantCulture The InvariantCulture property can be used to persist data in a culture-independent format. This provides a known format that does not change For using invariant format in converting string to DateTime your string value must be formatted with one of...
Visual Basic Datagrid View change row colour
vb.net,datagridview,datagrid
Is it possible that your datagridview isn't loaded fully when you try to recolor the rows? Since you are setting the datasource, you should put your code that affects the grid after you can make sure that it is finished loading. The column widths change because it is not dependent...
Outlook 2013 Cannot create ActiveX component from ASP.NET Application
asp.net,vb.net,outlook,office-interop
No Office app (including Outlook) can run in a service (such as IIS). Your options are Extended MAPI (C++ or Delphi only), Redemption (which wraps Extended MAPI and can be accessed from any language, including C#), EWS (Exchange only) or straight SMTP.
jQuery create a real-time array from multiple inputs with the same class
jquery,html,arrays,class
Your current code is changing emailObj from an object to a string on each iteration of the loop, instead of amending a property of the object itself. Also note that you can use the . style selector to match elements by their class. To achieve what you require, you can...
How do I use VB.NET to send an email from an Outlook account?
vb.net,email
change the smtpserver from smtp.outlook.com to smtp-mail.outlook.com web.config settings <mailSettings> <smtp deliveryMethod='Network' from='[email protected]'> <network host='smtp-mail.outlook.com' userName='[email protected]' password='passwordhere' port='587' enableSsl='true'/> </smtp> </mailSettings> ...
Use String to find my.resources
The Designer creates property getters and setters for the images etc you add to Resources. So, for an image named dicedark1.jpg, it creates: Friend ReadOnly Property diceDark1() As System.Drawing.Bitmap Get Dim obj As Object = ResourceManager.GetObject('diceDark1', resourceCulture) Return CType(obj,System.Drawing.Bitmap) End Get End Property You can see these in Resources.Designer.vb. So...
Interpreting hex dump of java class file
java,class,hex
The 000000b0 is not part of the data. It's the memory address where the following 16 bytes are located. The two-digit hex numbers are the actual data. Read them from left to right. Each row is in two groups of eight, purely to asist in working out memory addresses etc....
Where to store an mp4 file in my project?
.net,vb.net,visual-studio,mp4
Try going Project>'Project Name' Properties>Resources>Add Resource>Add Existing File This should add the file into your resources folder. You can then access any file by going My.Resources.Name_Of_Resource...
Convert date to string format
vb.net,converter
Your approach doesn't work because you are using ToString on a DataColumn which has no such overload like DateTime. That doesn't work anyway. The only way with the DataTable was if you'd add another string-column with the appropriate format in each row. You should instead use the DataGridViewColumn's DefaultCellStyle: InvestorGridView.Columns(1).DefaultCellStyle.Format...
Automapper AfterMap function initialising classes
.net,vb.net,automapper
The objects have values in them because they are called after Mapping.Map function is called and that's where actual object with values is passed and then AfterMap function is called and that's how it has the values in it.
How to make existing forms deriven from a base form in VB.net
vb.net,inheritance
Since you want to change existing forms to inherit another base class you need to change each form that you want to take effect and change what they inherit. Go to each of your forms designer code class. Inside towards the top you will see the inherits statment. Change what...
Formatting a drive in Visual Basic?
vb.net,format,drive
The problem is that Process.Start does not take command line arguments in the first parameter. Use the overload that allows command line arguments. For example: Process.Start('format.com', 'H:'); ...
React components as plain JS objects?
javascript,class,reactjs,javascript-objects,ecmascript-6
React.Component is a plain javascript function, since es6 classes are syntactic sugar around them. So we could use whatever es5 class-like concept we like e.g. I just borrowed Backbone's extend method here: // From backbone var extend = function(protoProps) { var parent = this; var child; var extendObj = function(obj1,...
Get List of Elements in Tree with specific Field Value
vb.net,linq,properties,interface
If i have understood it correctly you want to get all selected parents and all selected children. You could use a recursive method: Public ReadOnly Property checkedList As List(Of TreeSelectorAttributes) Get Return rootList.Where(Function(t) t.SelectedInTreeSelector). SelectMany(Function(root) GetSelectedChildren(root)). ToList() End Get End Property Function GetSelectedChildren(root As TreeSelectorAttributes, Optional includeRoot As Boolean =...
Method nonvisibility of same instanceof but differing class
java,class,methods,visibility
You can use reflection APIs to call the exclusiveMethod . The code would look something like - Method m = var.getClass().getMethod('exclusiveMethod', null); if(m != null) { m.invoke(var, null); } You can get more information about relfection APIs here - http://docs.oracle.com/javase/tutorial/reflect/index.html Another way to get this is by casting the var...
Filtering Last Duplicate Occurrence In A Datatable
c#,vb.net
You can use LINQ: DataTable nonDups = parsedDataset.Tables('Detail').AsEnumerable() .GroupBy(row => row.Field<string>('Authorization_ID')) .OrderBy(grp => grp.Key) .Select(grp => grp.Last()) .CopyToDataTable(); This selects the last row of each dup-group. If you want to order the group use grp.OrderBy....
Can't output Guid Hashcode
sql,vb.net,guid,hashcode
Well, are you looking for a hashcode like this? 'OZVV5TpP4U6wJthaCORZEQ' Then this answer might be useful: Guid g = Guid.NewGuid(); string GuidString = Convert.ToBase64String(g.ToByteArray()); GuidString = GuidString.Replace('=','); GuidString = GuidString.Replace('+','); Extracted from here. On the linked post there are many other useful answers. Please take a look! Other useful links:...
vb.net AES decryption returns “data is incomplete block”
vb.net,encryption,cryptography,aes
Despite all comments, I still lack understanding of your intentions. Therefore, the sample code below may not provide what you exactly want, but at least should give an idea how to employ cryptographic functions. Particularly, the most notable difference from your approach is that the encryption key and initialization vector...
How to execute four queries once and then check success or failure?
vb.net,windows,visual-studio-2010,ms-access
There a number of other problems with the code (sql injection, sharing a connection among several commands), but here's a step in the right direction: Try conn.Open() cmdfoods.ExecuteNonQuery() cmdservices.ExecuteNonQuery() cmdreservations.ExecuteNonQuery() bill.ExecuteNonQuery() success = True Catch success = False Finally conn.Close() End Try A more-complete solution: Private Function save_to_data() Dim sql...
VB.net: How to define a namespace where the first segment is NOT the file name?
Remove the Root namespace from the project properties: ...
Syntax error in Insert query in Mysql in VB.Net
mysql,vb.net
you miss the closing parenthesis for the values list: Dim cmd1 As New OdbcCommand('insert into party values(' + pcode_txt.Text + ',' + Trim(UCase(name_txt.Text)) + ',' + Trim(UCase(addr_txt.Text)) + ',' + phone_txt.Text + ',' + combo_route.SelectedItem + ',' + combo_area.SelectedItem + ')', con) My answer is perfectly fit to your question...
Getting value of Date Time Picker and using BETWEEN for filtering date in Ms Access database
vb.net,ms-access,oledb
Change ...'WHERE today BETWEEN ' & fromdatestring & ' AND ' & todatestring & ''... To ...'WHERE today >= #' & fromdatestring & '# AND today <= #' & todatestring & '#'... Please note that MS-Access uses #-Delimiters for Date-Values (afaik), this could also be a problem in your query....
Generally speaking,a class is a software component that defines andimplements one or more interfaces. (Strictly speaking, a class neednot implement all the members of an interface. We discuss this laterwhen we talk about abstract members.) In different terms, a classcombines data, functions, and types into a new type. Microsoft usesthe term type to include classes.
Under VisualStudio.NET, a VB class module is inserted into a project using theAdd Class menu item on the Project menu. This inserts a new modulecontaining the code:
Although Visual Studio stores each class in a separate file, thisisn’t a requirement. It is the
Class
...End
Class
construct that marks the beginning and endof a class definition. Thus, the code for more than one class as wellas one or more code modules (which are similarly delimited by theModule
...End Module
construct)can be contained in a single source code file.The CPerson class defined in the next section is an example of a VBclass module.
In VB.NET, class modules cancontain the following types of members:
This includes member variables (also calledfields) and constants.
Events are procedures that are calledautomatically by the Common Language Runtime in response to someaction that occurs, such as an object being created, a button beingclicked, a piece of data being changed, or an object going out ofscope.
This refers to both functions andsubroutines. A function member is also called a method. Aclass’ constructor is a special type of method. Wediscuss constructors in detail later in this chapter.
A property member is implemented as aPrivate member variable together with a special type of VB functionthat incorporates both accessor functions of the property. We discussthe syntax of this special property function in Section 4.3.5 later in the chapter.
A class member can be another class, whichis then referred to as a nested class.
The following CPerson class illustrates some of the types of members:
We have seen that, when speaking ingeneral object-oriented terms, the exposed members of a softwarecomponent constitute the component’s publicinterface (or just interface). Now, in VB.NET, each member of aclassmodule has an access type, which may be
Public
, Private
,Friend
, Protected
, orProtected
Friend
. We discusseach of these in detail later in this chapter. Suffice it to say, aVB.NET class module may accordingly have Public
,Private
, Friend
,Protected
, and Protected
Friend
members.Thus, we face some ambiguity in defining the concept of the publicinterface of a VB.NET class. The spirit of the term might indicatethat we should consider any member that is exposed outside of theclass itself as part of the public interface of the class. This wouldinclude the
Protected
, Friend
,and Protected Friend
members, as well as thePublic
members. On the other hand, some mightargue that the members of the public interface must be exposedoutside of the project in which the class resides, in which case onlythe Public
members would be included in theinterface. Fortunately, we need not make too much fuss over the issueof what exactly constitutes a VB.NET class’ publicinterface, as long as we remain aware that the term may be useddifferently by different people.Aclassis just a description of some properties and methods and does nothave a life of its own (with the exception of shared members, whichwe discuss later). In general, to execute the methods and use theproperties of a class, we must create an instance of the class,officially known as an object. Creating an instance of a class isreferred to as instancing, orinstantiating, theclass.
There are three ways to instantiate an object of a VB.NET class. Onemethod is to declare a variable of the class’ type:
and then instantiate the object using the
New
keyword as follows:We can combine these two steps as follows:
or:
The first syntax is considered shorthand for the second.
Propertiesaremembers that can be implemented intwo different ways. In its simplest implementation, a property isjust a public variable, as in:
The problem with this implementation of the Age property is that itviolates the principle of encapsulation; anyone who has access to aCPerson object can set its Age property to any Integer value, evennegative integers, which are not valid ages. In short, there is noopportunity for data validation. (Moreover, this implementation of aproperty does not permit its inclusion in the public interface of theclass, as we have defined that term.)
The “proper” object-oriented way toimplement a property is to use a Private data member along with aspecial pair of function members. The Private data member holds theproperty value; the pair of function members, calledaccessors, are usedto get and set the property value. This promotes data encapsulation,since we can restrict access to the property via code in the accessorfunctions, which can contain code to validate the data. The followingcode implements the Age property:
As you can see from the previous code, VB has a special syntax fordefining the property accessors. As soon as we finish typing theline:
the VB IDE automatically creates the following template:
Note the
Value
parameter that providesaccess to the incoming value. Thus, if we write:then VB passes the value 20 into the Property procedure in the
Value
argument.Themembers of a classfall into two categories:
Membersthat can only be accessed through an instance of the class, that is,through an object of the class. To put it another way, instancemembers “belong” to an individualobject rather than to the class as a whole.
Members that can be accessed withoutcreating an instance of the class. These members are shared among allinstances of the class. More correctly, they are independent of anyparticular object of the class. To put it another way, shared members“belong” to the class as a whole,rather than to its individual objects or instances.
Instance members are accessed by qualifying the member name with theobject’s name. Here is an example:
To access a shared member, we simply qualify the member with theclass name. For instance, the String class in the System namespace ofthe .NET Framework Class Library has a shared method called Comparethat compares two strings. Its syntax (in one form) is:
This function returns 0 if the strings are equal, -1if the first string is less than the second, and 1 if the firststring is greater than the second. Since the method is shared, we canwrite:
Note the way the Compare method is qualified with the name of theString class.
Shared members are useful for keeping track of data that isindependent of any particular instance of the class. For instance,suppose we want to keep track of the number of CPerson objects inexistence at any given time. Then we write code such as thefollowing:
Now, code such as the following accesses the shared variable:
When anobjectof aparticular class is created, the compiler calls a special functioncalled the class’ constructoror instance constructor. Constructors can beused to initialize an object when necessary. (Constructors take theplace of the Class_ Initialize event in earlier versions of VB.)
We can define constructors in a class module. However, if we choosenot to define a constructor, VB uses a default constructor. Forinstance, the line:
invokes the default constructor of our CPerson class simply becausewe have not defined a custom constructor.
To define a custom constructor, we just define a subroutine namedNew within the class module. For instance,suppose we want to set the Name property to a specified value when aCPerson object is first created. Then we can add the following codeto the CPerson class:
Now we can create a CPerson object and set its name as follows:
or:
Note that because VB.NET supports function overloading (discussedlater in this chapter), we can define multiple constructors in asingle class, provided each constructor has a unique argumentsignature. We can then invoke any of the custom constructors simplyby supplying the correct number and type of arguments for thatconstructor.
Note also that once we define one or more custom constructors, we canno longer invoke the default (that is,parameterless) constructor with astatement such as:
Instead, to call a parameterless constructor, we must specificallyadd the constructor to the class module:
In VB6, aprogrammer can implement the Class_Terminate event toperform any clean up procedures before an object is destroyed. Forinstance, if an object held a reference to an open file, it might beimportant to close the file before destroying the object itself.
In VB.NET, the Terminate event no longer exists, and things arehandled quite differently. To understand the issues involved, we mustfirst discuss garbage collection.
When the garbage collector determines that an object is no longerneeded (which it does, for instance, when the running program nolonger holds a reference to the object), it automatically runs aspecial destructor methodcalled Finalize. However, it is important tounderstand that, unlike with the Class_Terminate event, we have noway to determine exactly when the garbage collector will call theFinalize method. We can only be sure that it will be called at sometime after the last reference to the object is released. Any delay isdue to the fact that the .NET Framework uses a system calledreference-tracing garbage collection, which periodically releases unused resources.
Finalize is a Protected method. That is, it can be called from aclass and its derived classes, but it is not callable from outsidethe class, including by clients of the class. (In fact, since theFinalize destructor is automatically called by the garbage collector,a class should never call its own Finalize method directly.) If aclass’ Finalize method is present, then it shouldexplicitly call its base class’ Finalize method aswell. Hence, the general syntax and format of the Finalize method is:
The benefits of garbage collection are that it is automatic and itensures that unused resources are always released without anyspecific interaction on the part of the programmer. However, it hasthe disadvantages that garbage collection cannot be initiateddirectly by application code and some resources may remain in uselonger than necessary. Thus, in simple terms, we cannot destroyobjects on cue.
We should note that not all resources are managed by the CommonLanguage Runtime. These resources, such as Windows handles anddatabase connections, are thus not subject to garbage collectionwithout specifically including code to release the resources withinthe Finalize method. But, as we have seen, this approach does notallow us or clients of our class to release resources on demand. Forthis purpose, the Framework Class Library defines a second destructorcalled Dispose. Its general syntax and usage is:
Note that classes that support this callable destructor mustimplement the
IDisposable
interface — hencethe Implements
statement just shown.IDisposable
has just one member, the Disposemethod.It is important to note that it is necessary to inform any clients ofthe class that they must call this method specifically in order torelease resources. (The technical term for this is themanual approach!)