Creating Simple Windows Forms Application using C#

1. Start Visual Studio.

2. Create a Windows Application called HelloWorld.

3. From the Toolbox, drag a Label control onto the form.

4. Double Click the label to add an event handler.

5. Insert the following code:

private void label1_Click(object sender, EventArgs e)

{

MessageBox.Show("Hello World");

}

How to create Windows Forms Application using C#

Create a Windows Application
Drag a Label
Drag a Label

Avoiding Temporary Strings in C# / Reduce Unnecessary Garbage Collection in C#

Appending strings to existing will produce garbage collection overhead for the program. Instead use Append method of StringBuilder class or Concat, Join methods of String class

The following code differentiates between both :

private void stringbuilder_example()

{

// Appending String - Garbage Collection - Immutable

string CompleteAddress = "";

CompleteAddress += "105, Annanagar ";

CompleteAddress += "Chennai ";

CompleteAddress += "Tamil Nadu ";

MessageBox.Show(CompleteAddress);

// Appending String - using String Builder

System.Text.StringBuilder CompleteAddress1 = new

System.Text.StringBuilder();

CompleteAddress1.Append( "105, Annanagar ");

CompleteAddress1.Append( "Chennai ");

CompleteAddress1.Append( "Tamil Nadu ");

// Error Code

//MessageBox.Show(CompleteAddress1);

// corrected Code

MessageBox.Show(CompleteAddress1.ToString() );

}

C# StringBuilder Class, C# StringBuilder Class Append Method, Appending Strings without Garbage Overhead, Avoiding Temporary Strings in C#, Reduce Unnecessary Garbage Collection in C#

Nullable Variables in C#

A type is said to be nullable if it can be assigned a value or can be assigned nullNothingnullptra null reference (Nothing in Visual Basic), which means the type has no value whatsoever. Consequently, a nullable type can express a value, or that no value exists. For example, a reference type such as String is nullable, whereas a value type such as Int32 is not. A value type cannot be nullable because it has enough capacity to express only the values appropriate for that type; it does not have the additional capacity required to express a value of null.

The Nullable<(Of <(T>)>) structure supports using only a value type as a nullable type because reference types are nullable by design.

The Nullable class provides complementary support for the Nullable<(Of <(T>)>) structure. The Nullable class supports obtaining the underlying type of a nullable type, and comparison and equality operations on pairs of nullable types whose underlying value type does not support generic comparison and equality operations.

A variable can be declared nullable as shown below

Nullable <bool> FlagComplete = null;

Scenario

Use nullable types to represent things that exist or do not exist depending on the circumstance. For example, an optional attribute of an HTML tag might exist in one tag but not another, or a nullable column of a database table might exist in one row of the table but not another.

You can represent the attribute or column as a field in a class and you can define the field as a value type. The field can contain all the valid values for the attribute or column, but cannot accommodate an additional value that means the attribute or column does not exist. In this case, define the field to be a nullable type instead of a value type.

Fundamental Properties

The two fundamental members of the Nullable<(Of <(T>)>) structure are the HasValue and Value properties. If the HasValue property for a Nullable<(Of <(T>)>) object is true, the value of the object can be accessed with the Value property. If the HasValue property is false, the value of the object is undefined and an attempt to access the Value property throws an InvalidOperationException.

string Sample;

Nullable <bool> FlagComplete = null;

if (FlagComplete.HasValue)

{

MessageBox.Show(Sample);

}

else

{Sample = "No Value";

MessageBox.Show(Sample);

FlagComplete = false;

}

Boxing and Unboxing

When a nullable type is boxed, the common language runtime automatically boxes the underlying value of the Nullable<(Of <(T>)>) object, not the Nullable<(Of <(T>)>) object itself. That is, if the HasValue property is true, the contents of the Value property is boxed. When the underlying value of a nullable type is unboxed, the common language runtime creates a new Nullable<(Of <(T>)>) structure initialized to the underlying value.

If the HasValue property of a nullable type is false, the result of a boxing operation is nullNothingnullptr a null reference (Nothing in Visual Basic). Consequently, if a boxed nullable type is passed to a method that expects an object argument, that method must be prepared to handle the case where the argument is nullNothingnullptr a null reference (Nothing in Visual Basic). When nullNothingnullptra null reference (Nothing in Visual Basic) is unboxed into a nullable type, the common language runtime creates a new Nullable<(Of <(T>)>) structure and initializes its HasValue property to false.

The best overloaded Add method 'name for the collection initializer has some invalid arguments in ‘ToString’

The type of one argument in a method does not match the type that was passed when the class was instantiated.

The best overloaded method match for 'System.Windows.Forms.MessageBox.Show(string)' has some invalid arguments

Solution : One possible solution is to check if the ‘ToString’ has braces

System.Text.StringBuilder CompleteAddress1 = new

System.Text.StringBuilder();

CompleteAddress1.Append( "105, Annanagar ");

CompleteAddress1.Append( "Chennai ");

CompleteAddress1.Append( "Tamil Nadu ");

‘ Error Line

MessageBox.Show(CompleteAddress1.ToString );

‘ Solution

MessageBox.Show(CompleteAddress1.ToString() );

Argument '1': cannot convert from 'method group' to 'string'

The best overloaded Add method 'name for the collection initializer has some invalid arguments in ‘ToString’ Error

Argument '1': cannot convert from 'System.Text.StringBuilder' to 'string'

Use ‘ToString’ to convert the StringBuilder to String

// Appending String - using String Builder

System.Text.StringBuilder CompleteAddress1 = new

System.Text.StringBuilder();

CompleteAddress1.Append( "105, Annanagar ");

CompleteAddress1.Append( "Chennai ");

CompleteAddress1.Append( "Tamil Nadu ");

// Error Code

//MessageBox.Show(CompleteAddress1);

// corrected Code

MessageBox.Show(CompleteAddress1.ToString() );

Argument '1': cannot convert from 'System.Text.StringBuilder' to 'string' Error

Use of unassigned local variable 'name'

The C# compiler does not allow the use of uninitialized variables. If the compiler detects the use of a variable that might not have been initialized, it generates CS0165.

string Sample;

Nullable <bool> FlagComplete = null;

if (FlagComplete.HasValue)

{

MessageBox.Show(Sample);

}

Use new to create an instance of an object or assign a value

string Sample = "";

Nullable <bool> FlagComplete = null;

if (FlagComplete.HasValue)

{

MessageBox.Show(Sample);

}

else

If you want to have null for the variable Sample, declare it as Nullable ()