C# Discussion Boards - CodeProject

Re: Check if user can write and delete from a directory

25-Jul-10 14:17

In a Windows (C#) form, I need to check if the user has the required permissions to write and delete from a directory (that they select).
I have some code that will do the job, but it feels wrong.
I try writing and deleting a test file and if an exception is thrown, then the test fails.
I am a bit unhappy with using exception testing like this, but can't find any other method that does not require reams of code.

Does anyone have another method that does not require exception testing?

Here is my code.
WriteToLog(string Message, Enum LogType) is a general logging method that writes the first parameter to the log file identified by the second parameter.

private bool UserCanWrite()
{
    try
    {
        WriteToLog("Test", LogFiles.Test);

        string TestLogPath = "Failed.Log";

        if (BaseDirectory.Length == 0)
        {
            TestLogPath = string.Format("C:\\{0}", TestLogPath);
        }
        else
        {
            TestLogPath = string.Format("{0}\\{1}", BaseDirectory, TestLogPath);
        }

        FileInfo TestLog = new FileInfo(TestLogPath);
        TestLog.Delete();

        return true;
    }

    catch
    {
        MessageBox.Show("You Don't have Read, Write and Delete privileges on the selected Base Directory\n\nPlease have your System Administrator grant those privileges before proceeding", "Higher Level of Privileges Needed", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        return false;
    }

Not Active25-Jul-10 15:37

Not Active

25-Jul-10 15:37

You should use Code Access Security either declaratively or programatically make a demand for the appropriate permissions.

http://msdn.microsoft.com/en-us/library/system.security.permissions.fileiopermission.aspx[^]

I know the language. I've read a book. - _Madmatt

Re: Check if user can write and delete from a directory

RCoate25-Jul-10 20:07

Re: Check if user can write and delete from a directory

25-Jul-10 20:07

Thanks Mark,
I will check it out.

RCoate25-Jul-10 20:25

Re: Check if user can write and delete from a directory

25-Jul-10 20:25

I just had a look at the sample code, and they are using a try/catch exception block as well.

FileIOPermission f2 = new FileIOPermission(FileIOPermissionAccess.Read, "C:\\test_r");
f2.AddPathList(FileIOPermissionAccess.Write | FileIOPermissionAccess.Read, "C:\\example\\out.txt");
try
{
    f2.Demand();
}
catch (SecurityException s)
{
    Console.WriteLine(s.Message);
}

Apart from adding another couple of usings to my code and being a bit shorter, I don't know that this is an improvement.
Is there a reason that the above is better practice than the code I wrote?

Not Active26-Jul-10 1:22

Not Active

26-Jul-10 1:22

I also said CAS can be declaritive, as in specify an attribute not code; however if you read more about CAS, as you should, you will understand its use and get beyond your naive comments. There is more to coding than just counting the number of lines.

I know the language. I've read a book. - _Madmatt

Re: Check if user can write and delete from a directory

PIEBALDconsult25-Jul-10 18:58

Re: Check if user can write and delete from a directory

25-Jul-10 18:58

Checking for that sort of thing before you need it is generally not worthwhile -- things change. And maybe the user won't try writing or deleting anyway so you've wasted your time.

Simply let the user try, then deal with any Exceptions that occur at that point.

RCoate25-Jul-10 20:06

Re: Check if user can write and delete from a directory

25-Jul-10 20:06

This is where the user tries.
The Application reads an XML File and does a bunch of processing of documents in the selected directory.
There are a number of log files that need to be created and the processing should not occur if the log files can not be written.

Due to how the application is installed and used (Admin installs, normal user then runs) the user may not always have the appropriate level of access.
Life would be so much easier without users.

PIEBALDconsult26-Jul-10 3:02

Capture streaming video - (create bitmap)

26-Jul-10 3:02

Sure, so just before you start, begin writing the log file -- "Processing begun by <user> at <date time> ... Reading file <filename> ... "

RCoate wrote:
Life would be so much easier without users.

Yes, yes it is. I write mostly Windows Services and batch processing.

Mark H Bishop25-Jul-10 11:41

Mark H Bishop

25-Jul-10 11:41

Our watershed group has an IP camera that serves a video stream via a java applet. When we navigate to the camera's web page we see the video streem. The front end of thecode behind the camera's serving page is Is included below.

I am writing a C# Windows Application that has a webbrowser control that navigates to the page. I want to capture still images with a timer tick event. Right now, I have an hack that does a copy from screen on the webbrowser control:

Bitmap BMP_now = new Bitmap(webBrowser1.ClientSize.Width, webBrowser1.ClientSize.Height);
Graphics g = Graphics.FromImage(BMP_now);
g.CopyFromScreen(this.PointToScreen(webBrowser1.Location), new Point(0, 0), webBrowser1.ClientSize);
g.Dispose();

This cumbersome approach has the major drawback that the windows form must always be topmost. There's gotta be a better way.

Here's the source behing the IP Camera's page:

lt;html>
<head>
<TITLE>TRENDnet | CS-7835E0(TV-IP100)</TITLE>
<META http-equiv=Content-Type content="text/html; charset=windows-1252">
<link rel="stylesheet" href="style.css" type="text/css">
<script language="JavaScript"> 
<!--
function MM_preloadImages() { //v3.0
  var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
    var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i<a.length; i++)
    if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}
 
function MM_openBrWindow(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}
 
function MM_swapImgRestore() { //v3.0
  var i,x,a=document.MM_sr; for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}
 
function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}
 
function MM_swapImage() { //v3.0
  var i,j=0,x,a=MM_swapImage.arguments; document.MM_sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=MM_findObj(a[i]))!=null){document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}
//-->
</script>
<style type=text/css> 
A:link {FONT-WEIGHT: bold; FONT-SIZE: 14px; COLOR: ff6600; FONT-FAMILY: arial,geneva,sans-serif}
A:visited {FONT-WEIGHT: bold; FONT-SIZE: 14px; COLOR: ff6600; FONT-FAMILY: arial,geneva,sans-serif}
.org-news {FONT-WEIGHT: bold; FONT-SIZE: 12px; COLOR: ff6600; FONT-FAMILY: arial,geneva,sans-serif}
</style>
</head>
 
<script language="JavaScript"> 
function Init() {
    if ((navigator.appName != "Netscape") &&
        (navigator.userAgent.indexOf('Opera') == "-1"))
    {
       window.setInterval("ShowFrameRate()", 1000);
    }
}
 
function ShowFrameRate() {
    if (1)
    {
       var fFrameRate = cvcs.GetFrameRate();
       window.status = "Frame:" + fFrameRate.toString() + " fps";
    }
    cvcs.GetRealTimeData() ;
    CurrentTime.innerHTML = cvcs.GetTimeString();
    GetTrigger();
}
 
function GetTrigger() {
    if (cvcs.GetImageUpload() == 1) {
       ImageUpload.innerHTML = "[ON]";
    }
    else {
       ImageUpload.innerHTML = "[OFF]";
    }
    if (cvcs.GetImageEmail() == 1) {
       EmailImage.innerHTML = "[ON]";
    }
    else {
       EmailImage.innerHTML = "[OFF]";
    }
}
</script>

Re: Capture streaming video - (create bitmap)

Mark H Bishop26-Jul-10 12:31

Mark H Bishop

26-Jul-10 12:31

OK, so I discovered the mshtml namespace.

There is a tutorial at http://www.developerfusion.com/code/4712/generate-an-image-of-a-web-page/[^]

The example uses an interface (IHTMLDocument2) and creates an instance of another interface (IHTMLElement) from the document's body. From here it is a render and draw operation. Trouble is, the procedure does not render the applet's stream to the page. Rather, it shows the (blank) html target page that the applet streams into.

However, the mshtml namespace appears to be rich in interfaces, none of which are well documented. It appears that IHTMLElement can be instantiated with other document properties (besides “body) such as “applet” which in turn has an items collection. I have had no luck on this glory path yet. Any ideas?

convert an array of string

mrkeivan25-Jul-10 10:59

mrkeivan

25-Jul-10 10:59

Hey guys, I ve got this question, I tried to look for it online but haven't been lucky!
I've got this:

string[] names = new string[] { "Alan Smith", "Anne Dodsworth", "Boyan Mastoni", "Richard Duncan"};

Now I want to fill it from database, so I used a generic list

public List<string> ClassroomList = new List<string>();

then fill it with data from database,
but when I want to assign it to my string I get an error and can't convert it ....

string[] names = new string[10];
foreach (var item in ClassroomList)
{
    for (int i = 0; i < names.Length; i++)
    {
        names[i] = item;
    }
}

please help me out.

thanx

harold aptroot25-Jul-10 11:05

harold aptroot

25-Jul-10 11:05

What you are doing there is very odd, filling the array first with the first item, then with the second item, etc.. Eventually you'd have an array with 10 times the same string (the last one in ClassroomList), not a very useful way to spend CPU cycles.

What is your intent? What is the error?

Luc Pattyn25-Jul-10 11:20

Luc Pattyn

25-Jul-10 11:20

public List<string> ClassroomList = new List<string>();
...
string[] names=ClassroomList.ToArray();

would probably do it (and it takes care of the array dimension as well, without imposing an artificial limit such as the 10 you had).

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

PIEBALDconsult25-Jul-10 12:10

25-Jul-10 12:10

0) Don't use var

1) Don't use foreach in this case

2) Why copy a perfectly good List to an array?
3) If you need an array, why use the List?

Luc Pattyn25-Jul-10 12:55

Luc Pattyn

25-Jul-10 12:55

there's more questions than answers here.

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

PIEBALDconsult25-Jul-10 13:02