06 - WinForms - Validation, Exceptions, ListView, TreeView.md

Windows Forms – Validation, Exceptions, ListView, TreeView

• 1. Objectives
• 2. Data Validation
• 3. Complex Visualization Controls
  • 3.1. ListView
  • 3.2. TreeView
• 4. Exception Handling
  • 4.1. Custom Exceptions
  • 4.2. Standard Exceptions
• 5. Bibliography

1. Objectives

2. Data Validation

Assignment

Sample Code available – Check the “ValidationCustomExceptions” Sample

1. Create a new project with the name “ValidationCustomExceptions”

2. Create the following UI:
   

3. Add an ErrorProvider and name it errorProvider.

4. Add a method for validating the "Last Name" as follows:

   private bool IsLastNameValid()
   {
   	return string.IsNullOrWhiteSpace(tbLastName.Text.Trim());
   }

5. Handle the Validating event on tbLastName as follows:

   if (!IsLastNameValid())
   {
   	e.Cancel = true; //prevents the user from changing the focus to another control
   	errorProvider.SetError((Control)sender, "Last Name is empty!");
   }

6. Handle the Validated event on tbLastName as follows:

   //https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.errorprovider.clear
   errorProvider.SetError((Control)sender, string.Empty);

7. (optional) Set AutoValidate form property to EnableAllowFocusChange in order to allow the user to change the focus to a different control or to close the form.

8. Handle the Validating and Validated events for the tbFirstName in a similar manner

9. Handle the Click event on the “Add Participant” button as follows

   private void btnAdd_Click(object sender, EventArgs e)
   {
   	//https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.containercontrol.validatechildren
   	if (!ValidateChildren())
   	{
   		//An ErrorProvider control should
   		MessageBox.Show("The form contains errors!",
   			"Error",
   			MessageBoxButtons.OK,
   			MessageBoxIcon.Error);
   
   		return;
   	}
   }

10. Why is it recommended to have the validations both on the individual controls and in the handler for the “Add Participant” button?

3. Complex Visualization Controls

3.1. ListView

Assignment

Sample Code avilable – Check the “ListViewSample” Sample

1. Create a new project with the name “ListViewSample”

2. Rename Form1 to MainForm

3. Create the following UI:
   

4. Add a new folder to your project and name it “Entities”

5. Inside the “Entities” folder add the following “Participant” class:

   internal class Participant
   {
   	public string LastName { get; set; }
   	public string FirstName { get; set; }
   	public DateTime BirthDate { get; set; }
   
   
   	public Participant(string lastName, string firstName, DateTime 	birthDate)
   	{
   		LastName = lastName;
   		FirstName = firstName;
   		BirthDate = birthDate;
   	}
   }

6. Final form of the MainForm class

   public partial class MainForm : Form
   {
   	#region Properties
   	private List<Participant> _participants;
   	#endregion
   
   	public MainForm()
   	{
   		InitializeComponent();
   
   		_participants = new List<Participant>();
   	}
   
   	public void DisplayParticipants()
   	{
   		lvParticipants.Items.Clear();
   
   		foreach (Participant participant in _participants)
   		{
   			var listViewItem = new ListViewItem(participant.LastName);
   			listViewItem.SubItems.Add(participant.FirstName);
   			listViewItem.SubItems.Add(participant.BirthDate.ToShortDateString());
   
   			//approximate calculation of the age 
   			if ((DateTime.Now - participant.BirthDate).TotalDays / 365 >= 18)
   				listViewItem.ImageKey = "adult.png";
   			else
   				listViewItem.ImageKey = "child.png";
   
   			lvParticipants.Items.Add(listViewItem);
   		}
   	}
   
   	#region Events
   	private void btnAdd_Click(object sender, EventArgs e)
   	{
   		string firstName = tbFirstName.Text;
   		string lastName = tbLastName.Text;
   		DateTime birthDate = dtpBirthDate.Value;
   
   		var participant = new Participant(lastName, firstName, birthDate);
   		_participants.Add(participant);
   
   		DisplayParticipants();
   	}
   	#endregion
   }

7. Add buttons for changing the current “View” of the list, as shown:
   

8. Display the participants in groups (“Children” and “Adults”) as in the previous image

Homework

1. Also clear/reset the values in the textboxes and in the DateTimePicker when the user clicks the "Add Participant" button

3.2. TreeView

Assignment

Sample Code available – Check the “TreeViewSample” Sample

1. Create a new project with the name “TreeViewSample”

2. Create the following UI:
   

3. Add the following methods:

    #region Methods
   private void FillDirectoryTree()
   {
   	//  Suppress redraw until tree view is complete
   	tvw.BeginUpdate();
   
   	//  First clear all the nodes.
   	tvw.Nodes.Clear();
   
   	//  Get the logical drives and put them into the root nodes.
   	//  Fill an array with all the logical drives on the machine.
   	string[] strDrives = Environment.GetLogicalDrives();
   
   	//  Iterate through the drives, adding them to the tree.
   	//  Use a try/catch block, so if a drive is not ready, 
   	//  e.g. an empty floppy or CD, it will not be added to the tree.
   	foreach (string rootDirectoryName in strDrives)
   	{
   		try
   		{
   			//  Find all the first level subdirectories.
   			//  If the drive is not ready, this will throw an 
   			//  exception, which will have the effect of 
   			//  skipping that drive.
   			Directory.GetDirectories(rootDirectoryName);
   
   			//  Create a node for each root directory
   			TreeNode ndRoot = new TreeNode(rootDirectoryName);
   
   			//  Add the node to the tree
   			tvw.Nodes.Add(ndRoot);
   
   			//  Add subdirectory nodes.
   			//  If Show Files checkbox checked, then also get the filenames.
   			GetSubDirectoryNodes(ndRoot, cb.Checked);
   		}
   		catch (IOException)
   		{
   			//  let it through
   		}
   		catch (Exception e)
   		{
   			//  Catch any other errors.
   			MessageBox.Show(e.Message);
   		}
   	}
   
   	tvw.EndUpdate();
   
   }
   
   private void GetSubDirectoryNodes(TreeNode parentNode, bool getFileNames)
   {
   	//  Exit this method if the node is not a directory.
   	DirectoryInfo di = new DirectoryInfo(parentNode.FullPath);
   	if ((di.Attributes & FileAttributes.Directory) == 0)
   	{
   		return;
   	}
   
   	//  Clear all the nodes in this node.
   	parentNode.Nodes.Clear();
   
   	try
   	{
   		//  Get an array of strings containing all the subdirectories in the parent node.
   		string[] arSubs = Directory.GetDirectories(parentNode.FullPath);
   
   		//  Add a child node for each subdirectory.
   		foreach (var subDir in arSubs)
   		{
   			DirectoryInfo dirInfo = new DirectoryInfo(subDir);
   			// do not show hidden folders
   			if ((dirInfo.Attributes & FileAttributes.Hidden) != 0)
   			{
   				continue;
   			}
   
   			TreeNode subNode = new TreeNode(dirInfo.Name);
   			subNode.ImageIndex = 0;
   			subNode.SelectedImageKey = "openFolder.png";
   			parentNode.Nodes.Add(subNode);
   		}
   
   		if (getFileNames)
   		{
   			//  Get any files for this node.
   			string[] files = Directory.GetFiles(parentNode.FullPath);
   
   			// After placing the nodes, 
   			// now place the files in that subdirectory.
   			foreach (string str in files)
   			{
   				FileInfo fi = new FileInfo(str);
   				TreeNode fileNode = new TreeNode(fi.Name);
   				parentNode.Nodes.Add(fileNode);
   
   				//  Set the icon
   				switch (fi.Extension.ToUpper())
   				{
   					case ".JPG":
   					case ".JPEG":
   						fileNode.ImageKey = "jpgFile.png";
   						fileNode.SelectedImageKey = "jpgFile.png";
   						break;
   					case ".TXT":
   						fileNode.ImageKey = "textFile.png";
   						fileNode.SelectedImageKey = "textFile.png";
   						break;
   					default:
   						fileNode.ImageKey = "file.png";
   						fileNode.SelectedImageKey = "file.png";
   						break;
   				}
   			}
   		}
   	}
   	catch (UnauthorizedAccessException)
   	{
   
   	}
   }
   #endregion

4. Exception Handling

4.1. Custom Exceptions

Assignment

Sample Code available – Check the “ValidationCustomExceptions” Sample

1. Add the following “InvalidBirthDateException” class:

   public class InvalidBirthDateException : Exception
   {
   	public DateTime BirthDate { get; set; }
   
   	public InvalidBirthDateException(DateTime birthDay)
   	{
   		BirthDate = birthDay;
   	}
   
   	public override string Message
   	{
   		get
   		{
   			return "The birthDate " + BirthDate + " is invalid";
   		}
   	}
   }

2. Update the “BirthDate” property in the “Participant” class in order to validate the received value:

   #region BirthDate
   private DateTime _birthDate;
   public DateTime BirthDate {
   	get { return _birthDate; }
   	set
   	{
   		if(value >= DateTime.Today)
   			throw new InvalidBirthDateException(value);
   		_birthDate = value;
   	}
   }
   #endregion

3. Update the event handler for the “Add Participant” button in order to handle the potential exceptions:

   try
   {
   	var participant = new Participant(lastName, firstName, birthDate, gender, ssn);
   	//TODO Logic for adding the participant to the list below
   }
   catch (InvalidBirthDateException ex)
   {
   	//Expected exception
   	MessageBox.Show(string.Format("The birth date {0} is invalid!", ex.BirthDate));
   }
   catch (Exception)
   {
   	//UnExpected exception
   	MessageBox.Show("An exception has been encountered! Please contact the technical support.");
   
   	//Log the exception using:
   	// - Log4Net
   	// - Application Insights
   }
   finally
   {
   	Debug.WriteLine("Always executed");
   }

4.2. Standard Exceptions

• common exception types: System.NotImplementedException, System.DivideByZeroException, System. FormatException

Further reading: link

Assignment

1. Create a new project with the name “StandardExceptions”

2. Create the following UI:
   

3. Handle the possible exceptions

    try
   {
   	int value1 = int.Parse(tbValue1.Text);
   	int value2 = int.Parse(tbValue2.Text);
   
   	tbResult.Text = (value1/	value2).ToString(CultureInfo.InvariantCulture);
   
   	//Throwing an exception:
   	//throw new NotImplementedException();
   }
   catch (FormatException ex)
   {
   	MessageBox.Show(ex.Message);
   
   	//Rethrowing the exception
   	//throw; //Handled by Program.Application_ThreadException
   }
   catch (DivideByZeroException ex)
   {
   	MessageBox.Show(ex.Message);
   }
   catch (Exception ex)
   {
   	MessageBox.Show(ex.Message);
   }

4. Catching all uncaught exceptions in an application can be done by subscribing to the “ThreadException” event in the “Program” class

   static class Program
   {
   	/// <summary>
   	/// The main entry point for the application.
   	/// </summary>
   	[STAThread]
   	static void Main()
   	{
   		Application.ThreadException += Application_ThreadException;
   
   		Application.EnableVisualStyles();
   		Application.SetCompatibleTextRenderingDefault(false);
   		Application.Run(new MainForm());
   	}
   
   	private static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e)
   	{
   		MessageBox.Show(e.Exception.Message);
   	}
   }

5. Bibliography

• ErrorProvider Class: https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.errorprovider
• How to: Display Error Icons for Form Validation with the Windows Forms ErrorProvider Component: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/display-error-icons-for-form-validation-with-wf-errorprovider