​​async, await, and Task (part 4)

If you have multiple async methods that return the values then you can use await for all methods just before you want to use the return value in further steps.

In the above program, we do await result1 and await result2 just before we need to pass the return value to another method.

Thus, you can use async, await, and Task to implement asynchronous programming in .NET Framework or .NET Core using C#.

💬 The channel has been running since 2018. It needs your support: https://www.patreon.com/csharp1001notes

Difference between static, readonly, and constant in C# (part 1)

static:

🔸 Declared using the static keyword.

🔸 Classes, constructors, methods, variables, properties, event and operators can be static. The struct, indexers, enum, destructors, or finalizers cannot be static.

🔸 Static members can only be accessed within the static methods. The non-static methods cannot access static members.

🔸 Value of the static members can be modified using ClassName.StaticMemberName.

🔸 Static members can be accessed using ClassName.StaticMemberName, but cannot be accessed using object.

Difference between static, readonly, and constant in C# (part 2)

readonly:

🔸 Declared using the readonly keyword.

🔸 Only the class level fields can be readonly. The local variables of methods cannot be readonly.

🔸 Readonly fields can be initialized at declaration or in the constructor. Therefore, readonly variables are used for the run-time constants.

🔸 Readonly variable cannot be modified at run-time. It can only be initialized or changed in the constructor.

🔸 Readonly members can be accessed using object, but not ClassName.ReadOnlyVariableName.

Difference between static, readonly, and constant in C# (part 3)

const:

🔸 Declared using the const keyword. By default a const is static that cannot be changed.

🔸 Only the class level fields or variables can be constant.

🔸 The constant fields must be initialized at the time of declaration. Therefore, const variables are used for compile-time constants.

🔸 Constant variables cannot be modified after declaration.

🔸 Const members can be accessed using ClassName.ConstVariableName, but cannot be accessed using object.

​​Difference between static, readonly, and constant in C# (part 4)

The following example demonstrates the difference between static, readonly, and const variables.

💬 Like this note? Want to support the channel? Become a patron: https://www.patreon.com/csharp1001notes

​​IndexOutOfRangeException in C# (part 1)

The IndexOutOfRangeException is an exception that will be thrown while accessing an element of a collection with an index that is outside of its range. It occurs when an invalid index is used to access a member of a collection.

The following example throws the IndexOutOfRange exception:

In the above example, an arr contains five elements. It will throw an IndexOutOfRange exception when trying to access value more than its total elements. Above, trying to access the 6th element using arr[5] will throw IndexOutOfRange exception.

​​Solutions to Prevent IndexOutOfRangeException (part 2)

Solution 1: Get the total number of elements in a collection and then check the upper bound of a collection is one less than its number of elements.

The following example shows how to fix IndexOutOfRange exception:

​​Solutions to Prevent IndexOutOfRangeException (part 3)

Solution 2: Use the try catch blocks to catch the IndexOutOfRangeException.

In the above example, the entire code wrapped inside the try block may throw errors. The catch block has the Exception filter that can catch any exceptions. So, when the arr[5] statement inside the try block throws an exception, the catch block captures the IndexOutOfRange exception and displays an error message, and continues the execution.

💬 If you appreciate this channel and want it to grow, why not support it: https://www.patreon.com/csharp1001notes

​​Foreach Loop in C# (part 2)

Important Points:

🔸 The foreach loop iterate only in forward direction.

🔸 Performance wise foreach loop takes much time as compared with for loop.

🔸 Because internally it uses extra memory space as well as.

🔸 The foreach loop use GetEnumarator() method of the IEnumerable interface. So, the foreach loop can be used with any class that has implemented the interface.

🔸 Exit the foreach loop by using break, return, Goto and throw.

The following example demonstrates the foreach loop on a dictionary collection.

​​Foreach Loop in C# (part 3)

As mentioned before, the foreach loop can be used to iterate any class that has implemented the IEnumerable interface. The following example demonstrates how to implement the IEnumerable interface in order to use the foreach loop with the custom class.

Above, the Shop class has implemented the IEnumerable interface that contains the GetEnumerator() method. This will enable the Shop class to be used with the foreach loop that returns the Customer objects.

​​Foreach Loop in C# (part 4)

Beginning with C# 8.0, you can use the await foreach statement to consume an asynchronous stream of data, that is, the collection type that implements the IAsyncEnumerable<T> interface. Each iteration of the loop may be suspended while the next element is retrieved asynchronously. The following example shows how to use the await foreach statement:

You can also use the await foreach statement with an instance of any type that satisfies the following conditions:

🔸 A type has the public parameterless GetAsyncEnumerator method. That method can be a type's extension method.

🔸 The return type of the GetAsyncEnumerator method has the public Current property and the public parameterless MoveNextAsync method whose return type is Task<bool>, ValueTask<bool>, or any other awaitable type whose awaiter's GetResult method returns a bool value.

By default, stream elements are processed in the captured context. If you want to disable capturing of the context, use the TaskAsyncEnumerableExtensions.ConfigureAwait extension method. For more information about synchronization contexts and capturing the current context, see Consuming the Task-based asynchronous pattern. For more information about asynchronous streams, see the Asynchronous streams section of the What's new in C# 8.0 article.

💬 Support the channel and its mission to help programmers learn C#: https://www.patreon.com/csharp1001notes

​​How to loop through an enum in C#? (part 1)

Here you will learn how to enumerate or loop through an enum.

In C#, an enum is used to assign constant names to a group of numeric integer values. It makes constant values more readable, for example, WeekDays.Monday is more readable than number 0 when referring to the day in a week.

An enum can be looped through using Enum.GetNames<TEnum>(), Enum.GetNames(), Enum.GetValues<TEnum>(), or Enum.GetValues() static methods with the foreach loop.

The following example gets the names of an enum using the Enum.GetNames<TEnum>() method.

​​How to loop through an enum in C#? (part 2)

The Enum.GetValues<TEnum>() is a static method that retrieves an array of the constant values of the specified enum.

The following example shows how to get the values of an enum using the Enum.GetValues<TEnum>() method.

💬 The channel has been running since 2018. It needs your support: https://www.patreon.com/csharp1001notes

​​NullReferenceException in C# (part 1)

The NullReferenceException is an exception that will be thrown while accessing a null object.

The following example shows the code that throws the NullReferenceException:

In the above example, a NullReferenceException will be thrown in the DisplayCities() function while accessing cities list using a foreach loop because the cities list is null. If the caller of the DisplayCities() function pass a null IList value then it will raise a NullReferenceException.

​​Solutions to fix the NullReferenceException (part 2)

To prevent the NullReferenceException exception, check whether the reference type parameters are null or not before accessing them.

Solution 1: Check whether an object contains a null value or not using an if condition, as shown below:

In the above example, if(cities == null) checks whether the cities object is null or not. If it is null then display the appropriate message and return from the function.

​​Solutions to fix the NullReferenceException (part 3)

In .NET 5, use the null conditional operator ?., as shown below:

In the above example, std?.FirstName is like if(std != null) std.FirstName. The std?.FirstName checks if std is not null then only access the FirstName property.

​​Solutions to fix the NullReferenceException (part 4)

In .NET 4.x and above versions, use Null-Coalescing operator ?? to prevent an exception, as shown below:

In the above example, ?? is a null coalescing operator that checks if an object is null or not, if it is null then create an object. The cities ?? new List<string>() creates a new list object if a cities is null in foreach loop. Thus, the NullReferenceException will be not be raised.

💬 Like this note? Want to support the channel? Become a patron: https://www.patreon.com/csharp1001notes