.NET interview questions: - How can we make Windows API calls in .NET?

Windows API calls are not COM based and they are invoked through Platform Invoke
Services.

Declare StringConversionType (Function | Sub) MethodName Lib "DllName" ([Args]) As Type

• StringConversionType is for what type of conversion should take place.Either we can specify Unicode to convert all strings to Unicode values, or Auto to convert strings according to the .NET runtime rules.
• MethodName is the name of the API to call.

• DllName is the name of the DLL.

• Args are any arguments to the API call.

• Type is the return type of the API call.

Below is a sample code for VB.NET, which uses Sleep windows API for delaying.

Public Class Form1

Declare Auto Sub Sleep Lib “kernel32.dll” (ByVal dwMilliseconds As Long)

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

MessageBox.Show(“ start sleeping for 5000 Milli seconds.....”)

Sleep(5000)

MessageBox.Show(“ end of sleeping.....”)

End Sub

End Class



#region Using directives



using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Windows.Forms;

using System.Runtime.InteropServices;

#endregion

namespace CSharpCode

{

partial class Form1 : Form

{

[DllImport(“Kernel32.dll”)]

static extern int Sleep(long dwMilliseconds);

public Form1()

{

InitializeComponent();

}

private void Form1_Load(object sender, EventArgs e)

{

MessageBox.Show(“Starting of 5000 ms...”);

Sleep(5000);

MessageBox.Show(“End of 5000 ms...”);

}

}

}

Also view our video on use of VAR keyword: -




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