The Beginners Guide To API
This article teaches you the basics of Windows API by giving you a walk through of Declaring API Functions from Start to Finish & uses real examples of useful code you can use in your Projects!
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<p><font size="2"><b>The Beginners Guide To API</b></font></p> <p><font size="2"><b>What is Windows API</b></font></p> <p><font size="2">It is Windows Application Programming Interface. This basically means that Windows has built in functions that programmers can use. These are built into its DLL files. (Dynamic Link Library)</font></p> <p><font size="2">So What can these functions do for me (you might ask) ?</font></p> <p><font size="2">These pre-built functions allow your program to do stuff without you actually have to program them.</font></p> <p><font size="2">Example: You want your VB program to Restart Windows, instead of your program communicating directly to the various bits & pieces to restart your computer. All you have to do is run the pre-built function that Windows has kindly made for you. This would be what you would type if you have VB4 32, or higher.</font></p> <p><font size="2">In your module</font></p> <p><font color="#000080" size="2"><b>Private</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Declare</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Function</b></font><font size="2"><b> ExitWindowsEx </b></font><font color="#000080" size="2"><b>Lib</b></font><font size="2"><b> "user32" (ByVal uFlags As Long, ByVal dwReserved As Long) As Long</b></font></p> <p><font size="2">If you wanted your computer to shutdown after you press Command1 then type this In your Form under</font></p> <p><font size="2">Sub Command1_Click ()</font></p> <p><font size="2"><b>X = ExitWindowsEx (15, 0) </b></font></p> <p><font size="2">End Sub </font></p> <p align="center"><font size="2">----------------</font></p> <p><font color="#000080" size="2"><b>Private</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Declare</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Function</b></font><font size="2"><b> ExitWindowsEx </b></font><font color="#000080" size="2"><b>Lib</b></font><font size="2"><b> "user32" (ByVal uFlags As Long, ByVal dwReserved As Long) As Long</b></font></p> <p><font size="2">Now to Explain what the above means</font></p> <p><font color="#000080" size="2"><b>Private</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Declare</b></font><font size="2"><b> </b></font><font color="#000080" size="2"><b>Function</b></font><font size="2"><b> ExitWindowsEx tells VB to Declare a Private Function called "ExitWindowsEx". </b></font></p> <p><font size="2">The<b> </b></font><font color="#000080" size="2"><b>Lib</b></font><font size="2"><b> "user32" </b>part tells VB that the function<b> ExitWindowsEx </b>is in the Library<b> (DLL file) </b>called<b> "user32". </b></font></p> <p><font size="2">The final part tells VB to expect the variables that the<b> ExitWindowsEx </b>function uses<b>. </b></font></p> <p><font size="2"><b>(ByVal uFlags As Long, ByVal dwReserved As Long) As Long</b></font></p> <p><font size="2">The <b>ByVal </b>means pass this variable by value instead of by reference.</font></p> <p><font size="2">The <b>As Long </b>tells VB what data type the information is.</font></p> <p><font size="2">You can find more about data types in your VB help files.</font></p> <p><font size="2">Now you should know what each part of the Declaration means so now we go on to what does</font></p> <p><font size="2"><b>X = ExitWindowsEx (15, 0)</b></font></p> <p><font size="2">For VB to run a function it needs to know where to put the data it returns from the function. The <b>X = </b>tells VB to put the response from <b>ExitWindowsEx </b>into the variable X. </font></p> <p><font size="2"><b>What's the point of X = </b></font></p> <p><font size="2">If the function runs or fails it will give you back a response number so you know what it has done.</font></p> <p><font size="2">For example if the function fails it might give you back a number other than 1 so you can write some code to tell the user this.</font></p> <p><font size="2">If x <> 1 Then MsgBox "Restart has Failed"</font></p> <p align="center"><font size="2">----------</font></p> <p><font size="2">Now you should know what everything in the Declaration above means. You are now ready to start using API calls in your own VB projects. </font></p> <p><font size="2"><b>To get you started I have included some useful API calls you might want to use that I've found on Planet Source Code.</b></font></p> <p><font size="2"><b>PLAY A WAVEFILE (WAV)</b></font></p> <p><font color="#000080" size="2">Declare</font><font size="2"> </font><font color="#000080" size="2">Function</font><font size="2"> sndPlaySound </font><font color="#000080" size="2">Lib</font><font size="2"> "winmm.dll" </font><font color="#000080" size="2">Alias</font><font size="2"> "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As Long) As Long </font></p> <p><font color="#000080" size="2">Public</font><font size="2"> </font><font color="#000080" size="2">Const</font><font size="2"> SND_SYNC = &H0 </font></p> <pre> <font color="#000080">Public</font> <font color="#000080">Const</font> SND_ASYNC = &H1 <font color="#000080">Public</font> <font color="#000080">Const</font> SND_NODEFAULT = &H2 <font color="#000080">Public</font> <font color="#000080">Const</font> SND_MEMORY = &H4 <font color="#000080">Public</font> <font color="#000080">Const</font> SND_LOOP = &H8 <font color="#000080">Public</font> <font color="#000080">Const</font> SND_NOSTOP = &H10</pre> <p><font size="2">Sub Command1_Click ()</font></p> <p><font size="2">SoundName$ = File 'file you want to play example "C:\windows\kerchunk.wav" </font></p> <pre> wFlags% = SND_ASYNC Or SND_NODEFAULT X = sndPlaySound(SoundName$, wFlags%)</pre> <p><font size="2">End sub</font></p> <p><font size="2"><b>CHANGE WALLPAPER</b></font></p> <p><font color="#000080" size="2">Declare</font><font size="2"> </font><font color="#000080" size="2">Function</font><font size="2"> SystemParametersInfo </font><font color="#000080" size="2">Lib</font><font size="2"> "user32" </font><font color="#000080" size="2">Alias</font><font size="2"> "SystemParametersInfoA" (ByVal uAction As Long, ByVal uParam As Long, ByVal lpvParam As Any, ByVal fuWinIni As Long) As Long </font></p> <pre> <font color="#000080">Public</font> <font color="#000080">Const</font> SPI_SETDESKWALLPAPER = 20 <font color="#000080"> </font>Sub Command1_Click () <font color="#000080">Dim</font> strBitmapImage As <font color="#000080">String </font>strBitmapImage = "c:\windows\straw.bmp" x = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, strBitmapImage, 0)</pre> <p><font size="2">End sub</font></p> <p><font size="2"><b>ADD FILE TO DOCUMENTS OF WINDOWS MENU BAR</b></font></p> <p><font color="#000080" size="2">Declare</font><font size="2"> </font><font color="#000080" size="2">Sub</font><font size="2"> SHAddToRecentDocs </font><font color="#000080" size="2">Lib</font><font size="2"> "shell32.dll" (ByVal uFlags As Long, ByVal pv As String)</font></p> <pre><font color="#000080">Dim</font> NewFile as <font color="#000080">String </font>NewFile="c:\newfile.file" Call SHAddToRecentDocs(2,NewFile)</pre> <p><font size="2">MAKE FORM TRANSPARENT</font></p> <pre><font color="#000080">Declare</font> <font color="#000080">Function</font> SetWindowLong <font color="#000080">Lib</font> "user32" <font color="#000080">Alias</font> "SetWindowLongA" _ (ByVal hwnd As Long, ByVal nIndex As Long,ByVal dwNewLong As Long) As Long <font color="#000080">Public</font> <font color="#000080">Const</font> GWL_EXSTYLE = (-20) <font color="#000080">Public</font> <font color="#000080">Const</font> WS_EX_TRANSPARENT = &H20&</pre> <p><font size="2">Private Sub Form_Load()</font></p> <p><font size="2">SetWindowLong Me.hwnd, GWL_EXSTYLE, WS_EX_TRANSPARENT</font></p> <p><font size="2">End</font></p> <p><font size="2">Any Problems email me at </font><a href="mailto:DSG@hotbot.com"><font size="2">DSG@hotbot.com</font></a><font size="2"> </font></p>
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