var controls = from control in this.Controls
                           select control;

But this will generate a compile time error – Could not find an implementation of the query pattern for source type ‘System.Windows.Forms.Control.ControlCollection’. ‘Select’ not found. Consider explicitly specifying the type of the range variable ‘control’. But the error was self explanatory, I need to specify the type of the control. And here is the modified version.

var controls = from Control control in this.Controls
                           select control;

And if you want to select specific type of controls you need to apply a where condition.

var textboxes = from Control textbox in this.Controls
                where textbox is TextBox
                select textbox;

There is some other inbuilt operators is also available to select specific controls, like OfType()

var textboxes = from textbox in this.Controls.OfType<TextBox>()
                select textbox;

In this method we don’t need to specify the type of the control in the from statement. And one of interesting LINQ extension method is the Cast<> method, which helps to enable the standard query operators to be invoked on non-generic collections by supplying the necessary type information. You can get more information from here.

I tried to print the document based on the ForeColor of the TextBox, but it was throwing some error, I couldn’t resolve itIts fixed. Source code is pretty self-explanatory. Happy Printing.

private int startIndex = 0;
private void printToolStripMenuItem_Click(object sender, EventArgs e)
{
    PrintDocument printDocument = new PrintDocument();
    //Print Options dialog.
    using (PrintDialog printDialog = new PrintDialog())
    {
        printDialog.ShowHelp = false;
        printDialog.ShowNetwork = false;
        printDialog.Document = printDocument;
        printDialog.AllowPrintToFile = true;
        //As its a simple text file, disabling the advanced options.
        printDialog.AllowCurrentPage = false;
        printDialog.AllowSelection = false;
        printDialog.AllowSomePages = false;
        //Display XP Style Print Dialog
        printDialog.UseEXDialog = true;
        if (printDialog.ShowDialog(this) == DialogResult.OK)
        {
            //Assigning the Printer settings to the Document.
            printDocument.PrinterSettings = printDialog.PrinterSettings;
            printDocument.PrintPage += new PrintPageEventHandler(printDocument_PrintPage);
            //Number of copies
            for (int i = 0; i < printDialog.PrinterSettings.Copies; i++)
            {
                startIndex = 0;
                //Print method call.
                printDocument.Print();
            }
        }
    }
}

And here is the Print Page event.

protected void printDocument_PrintPage(object sender, PrintPageEventArgs e)
{
    //Setting the color as Black.
    Brush brush = Brushes.Black;
    //Setting color dynamically
    //Brush brush = new SolidBrush(this.txtEditor.ForeColor);
    int lineCounter = 0;
    float lineTop = 0;
    //Looping throught each line in the textbox.
    for (int lineIndex = startIndex; lineIndex < this.txtEditor.Lines.Length; lineIndex++)
    {
        string line = this.txtEditor.Lines[lineIndex];
        lineCounter++;
        //Writing the line to the document.
        lineTop = e.MarginBounds.Top + lineCounter * this.txtEditor.Font.Size;
        e.Graphics.DrawString(line,
            this.txtEditor.Font,
            brush,
            e.MarginBounds.Left,
            lineTop);
        //Checking for more pages.
        if (lineTop > e.MarginBounds.Bottom)
        {
            startIndex = lineIndex;
            e.HasMorePages = true;
            return;
        }
    }
}

Open File Dialog in Visual Studio

We can also implement the same functionality in our applications by using CustomPlaces collection property of FileDialog class. The OpenFileDialog and SaveFileDialog classes allow you to add folders to the CustomPlaces collection.

openFileDialog.CustomPlaces.Add(@"C:\Users");

You can also specify GUID of Windows Vista known folder. Known Folder GUIDs are not case sensitive and are defined in the KnownFolders.h file in the Windows SDK. If the specified Known Folder is not present on the computer that is running the application, the Known Folder is not shown.

openFileDialog.CustomPlaces.Add(@"C:\Users");
//Desktop Folder
openFileDialog.CustomPlaces.Add(new Guid("B4BFCC3A-DB2C-424C-B029-7FE99A87C641"));
//Downloads Folder
openFileDialog.CustomPlaces.Add(new Guid("374DE290-123F-4565-9164-39C4925E467B"));

Open File Dialog with Custom Places

Note: This feature will not have any effect in Windows XP. Also you must set the AutoUpgradeEnabled to True(default) to enable this feature in Vista or Windows 7.

The following table lists few Windows Vista Known Folders and their associated Guid.

1. Contacts : 56784854-C6CB-462B-8169-88E350ACB882
2. ControlPanel : 82A74AEB-AEB4-465C-A014-D097EE346D63
3. Desktop : B4BFCC3A-DB2C-424C-B029-7FE99A87C641
4. Documents : FDD39AD0-238F-46AF-ADB4-6C85480369C7
5. Downloads : 374DE290-123F-4565-9164-39C4925E467B
6. Favorites : 1777F761-68AD-4D8A-87BD-30B759FA33DD
7. Fonts : FD228CB7-AE11-4AE3-864C-16F3910AB8FE
8. Music : 4BD8D571-6D19-48D3-BE97-422220080E43

This is a simple function which will return Network status using Ping Class.

using System.Net.NetworkInformation;
public bool IsNetworkAvailable()
{
	using (Ping ping = new Ping())
	{
		PingReply pingReply = ping.Send("www.google.com", 200);
		return pingReply.Status == IPStatus.Success;
	}
}

This sample code is doing some long operation in a separate thread and try to update the UI from the new thread.

private void Form1_Load(object sender, EventArgs e)
{
    this.threadStart = new ThreadStart(LongProcess);
    this.thread = new Thread(this.threadStart);
    this.thread.Start();
}
private void LongProcess()
{
    for (int i = 0; i < 100; i++)
    {
        Thread.Sleep(100);
        //This will throw an exception like this
        //System.InvalidOperationException - Cross-thread operation not valid:
        //Control 'textBox1' accessed from a thread other than the thread it was created on.
        this.textBox1.Text = i.ToString();
    }
}

And here is the source code which will fix the issue with delegates and Control.Invoke method

private ThreadStart threadStart;
private Thread thread;
private delegate void UpdateTextDelegate(string text);
private void Form1_Load(object sender, EventArgs e)
{
    this.threadStart = new ThreadStart(LongProcess);
    this.thread = new Thread(this.threadStart);
    this.thread.Start();
}

private void LongProcess()
{
    for (int i = 0; i < 100; i++)
    {
        Thread.Sleep(100);
        //This will resolve the cross thread invalid operation exception.
        this.UpdateText(i.ToString());
    }
}

private void UpdateText(string text)
{
    //Checks whether the called required to invoke the "Invoke" method.
    if (this.textBox1.InvokeRequired)
    {
        UpdateTextDelegate updateTextDelegate = new UpdateTextDelegate(UpdateText);
        //Calling the invoke method of the control with the parameter.
        this.textBox1.Invoke(updateTextDelegate, new object[] { text });
    }
    else
    {
        this.textBox1.Text = text;
    }
}

Thanks to Praveen for helping me out. Happing Coding

EDIT: In case WPF applications, we don’t have InvokeRequired property available for Controls. Instead we need to use Dispatcher.CheckAccess() method. We can rewrite the UpdateText method like the following

private void UpdateText(string text)
{
if (this.textbox1.Dispatcher.CheckAccess())
{
    this.textbox1.Content = text;
}
else
{
UpdateTextDelegate updateTextHandler = new UpdateTextDelegate(UpdateText);
this.textbox1.Dispatcher.Invoke(updateTextHandler, new object[] { text });
}
}

Thanks to Sivadas for his valueable comments.

We can access the Isolated Storage related classes from System.IO.IsolatedStorage namespace.

//Getting the User scoped Store corresponding to the calling codes assembly identity.
//IsolatedStorageFile class provides basic functionality to create files or folders.
IsolatedStorageFile isolatedStorageFile = IsolatedStorageFile.GetUserStoreForAssembly();
//Checking whether Directory Exists. Directory.Exists will not work. Also do some wildcard
//search like "dotnet*" or "dotnet?"
string[] directories = isolatedStorageFile.GetDirectoryNames("dotnetthoughts");
//Creating the directory if it is not exists.
if (directories.Length == 0)
{
    isolatedStorageFile.CreateDirectory("dotnetthoughts");
}
//IsolatedStorageFileStream encapsulates stream, used to create files
IsolatedStorageFileStream isolatedStorageFileStream =
    new IsolatedStorageFileStream(@"dotnetthoughts\\System.log",
        FileMode.OpenOrCreate, isolatedStorageFile);
//Writing the content to IsolatedStorage.
using (StreamWriter streamWriter = new StreamWriter(isolatedStorageFileStream))
{
    streamWriter.WriteLine("Hello Isolated Storage");
}
//Reading the contents from Isolated storage – If you try to read like this it will throw //exception.(Stream is not Readable)
using (StreamReader streamReader = new StreamReader(isolatedStorageFileStream))
{
    MessageBox.Show(streamReader.ReadToEnd());
}
isolatedStorageFileStream.Close();
isolatedStorageFile.Close();

There is some permission attributes too, which is used to grant code to access IsolatedStorage.

[IsolatedStorageFilePermission(SecurityAction.Demand)]
static class Program
{
//Code
}

The IsolatedStorage can be used in Silverlight assemblies too, which will helps to access local file system from Silverlight.