• Change names of controls
• Change sizes of controls using a mouse and modifying Size property
• ComboBox.DropDownStyle
• Use a double-click on a button to write code
• Code for pushing '=' button:
  

   int left = 0, right = 0, result = 0;
   if ( leftTextBox.Text.Length > 0 ) { 
   	left = int.Parse( leftTextBox.Text );
   }
   if ( rightTextBox.Text.Length > 0 ) {
  	right = int.Parse( rightTextBox.Text );
   }
   switch ( operatorComboBox.Text )
   {
  	case "-": result = left - right; break;
  	case "+": result = left + right; break;
  	case "*": result = left * right; break;
  	case "/": 
  		if ( right == 0 ) {					
  			MessageBox.Show( "Divide by 0", "Error", 
  				MessageBoxButtons.OK, MessageBoxIcon.Error );
  		} else { 
  			result = left / right;
  		}
  		break;
   }
   resultTextBox.Text = result.ToString();  

• Add event handler for Validated event
  

   string s = (sender as TextBox).Text;
   if ( s.Length > 0 ) {
  	try {
  		int v = int.Parse( s );
  		errorProvider.SetError( resultTextBox, "" );
  	}
  	catch ( Exception ) {
  		errorProvider.SetError( resultTextBox, "Not a number!" );
  	}
   } else {
  	errorProvider.SetError( resultTextBox, "" );
   }  

• Set Dock to Left
• Set Name to filesListView

• Set Name to imagePanel
• Set Dock to Fill
• Set BackColor to Black

• Set Name to statusBar

• Test changing window's size and position of the splitter

• Create group 'Directory' with options: 'Change', separator, 'Exit'
• Use '&' to underline a shortcut letter
• Use '-' to create a separator
• Change default names of options to more adequate

 if ( folderBrowserDialog.ShowDialog() == DialogResult.OK ) {
	try {
		filesListView.Items.Clear();
		DirectoryInfo di = new DirectoryInfo( folderBrowserDialog.SelectedPath );
		Environment.CurrentDirectory = folderBrowserDialog.SelectedPath;
		FileInfo []files = di.GetFiles();
		foreach ( FileInfo file in files ) {
			filesListView.Items.Add( file.Name );
		}
	}
	catch ( Exception ) {
	}
 }  

• Set Name to filesContextMenu
• Add three items: 'Large Icon', 'List', 'Details'
• Add event handlers for Click event
  

   filesListView.View = View.List;

• Set filesListView.ContextMenu to filesContextMenu

• Set Dock to Fill
• Set Visible to False
• Set Name to pictureBox

• Set Text to 'Not a image!'
• Set ForeColor to White
• Set Dock to Fill
• Set TextAlign to MiddleCenter
• Change Font to more visible
• Set Visible to False
• Set Name to notImageLabel

• Set MultiSelect to False
• Add event handler for SelectedIndexChanged
  

   ListView.SelectedListViewItemCollection selected = filesListView.SelectedItems;
   if ( selected.Count == 0 ) {
  	pictureBox.Visible = notImageLabel.Visible = false;
   } else {
  	string file = selected[0].Text;
      try {
  		pictureBox.Image = Image.FromFile( file );
  		pictureBox.Visible = true;
  		notImageLabel.Visible = false;
  	} 
  	catch ( Exception ) {
  		pictureBox.Visible = false;
  		notImageLabel.Visible = true;
  	}
   }  

• Add nameStatusBarPanel and sizeStatusBarPanel to Panels collection
• Set ShowPanels to True
• Add the following code to filesListView_SelectedIndexChanged()
  

   nameStatusBarPanel.Text = Environment.CurrentDirectory + '\\' + file;
   sizeStatusBarPanel.Text = string.Format( "{0} x {1}", 
  	pictureBox.Image.Width, pictureBox.Image.Height );  

• Set imagePanel.AutoScroll to True
• Add the following code to filesListView_SelectedIndexChanged()
  

   imagePanel.AutoScrollMinSize = new Size(
  	pictureBox.Image.Width, pictureBox.Image.Height );  

 if ( pictureBox.Image != null ) {
	Cursor = Cursors.WaitCursor;
	Color clr;
	int v;
	Bitmap bmp = new Bitmap( pictureBox.Image );
	for ( int x = 0; x < bmp.Width; x++ ) {
		for ( int y = 0; y < bmp.Height; y++ ) {
			clr = bmp.GetPixel( x, y );
			v = ( clr.R + clr.G + clr.B ) / 3;
			bmp.SetPixel( x, y, Color.FromArgb( v, v, v ));
		}
	}
	pictureBox.Image = bmp;
	Cursor = Cursors.Arrow;
 }  

• Set name of class to AboutForm
• Add option Help / About to the menu
  

   AboutForm about = new AboutForm();
   about.ShowDialog();  

• Run and test
• Set StartPosition to CenterParent
• Set ShowInTaskbar to False
• Set FormBorderStyle to FixedDialog
• Set MinimizeBox to False
• Set MaximizeBox to False

• Add event handler for Paint
  

   e.Graphics.FillRectangle( Brushes.White, 0, 0, 
  	ClientRectangle.Width, ClientRectangle.Height );
  
   Font font = new Font( "Verdana", 52, FontStyle.Bold );
   Brush specialBrush = new LinearGradientBrush( ClientRectangle,
  	Color.Yellow, Color.Red, 45, false );
   StringFormat sf = (StringFormat)StringFormat.GenericDefault.Clone();
   sf.Alignment = StringAlignment.Center;
   sf.LineAlignment = StringAlignment.Center;
   e.Graphics.DrawString( "I'm painting!", font, specialBrush,
  	ClientRectangle.Right/2, ClientRectangle.Bottom/2, sf );  

• Add member to AboutForm
  

   const int ballRadius = 50; 
   Point ballCenter = new Point( ballRadius, ballRadius );
   int ballSpeed = 5; 

• Add a Timer to AboutForm
• Add event handler for Tick
  

   ballCenter.X += ballSpeed;
   if ( ballCenter.X < ballRadius ) {
  	ballCenter.X = ballRadius;
  	ballSpeed = Math.Abs( ballSpeed );
   } else if ( ballCenter.X > ClientRectangle.Width - ballRadius ) {
  	ballCenter.X = ClientRectangle.Width - ballRadius;
  	ballSpeed = -Math.Abs( ballSpeed );
   }
   Invalidate();  

• Add the following code to AboutForm_Paint:
  

   e.Graphics.FillEllipse( Brushes.Black, 
  	ballCenter.X - ballRadius, ballCenter.Y - ballRadius,
  	2*ballRadius, 2*ballRadius );  

• Add handler for timer.Tick and call Invalidate()
• Add handler for AboutForm.Load and call timer.Start()
• Run and test

• Add the following code to form's constructor:
  

   SetStyle(ControlStyles.DoubleBuffer | ControlStyles.UserPaint | 
  	ControlStyles.AllPaintingInWmPaint, true);
   UpdateStyles();  

 private Bitmap bmpToGrayscale = null;
 private EventHandler onGrayscaleComplete;  

 private void OnGrayscaleComplete( object sender, EventArgs e ) {
	pictureBox.Image = bmpToGrayscale;
	grayscaleMenuItem.Enabled = true;
 }

 private void ThreadProc() {
	Color clr;
	int v;
	for ( int x = 0; x < bmpToGrayscale.Width; x++ ) {
		for ( int y = 0; y < bmpToGrayscale.Height; y++ ) {
			clr = bmpToGrayscale.GetPixel( x, y );
			v = ( clr.R + clr.G + clr.B ) / 3;
			bmpToGrayscale.SetPixel( x, y, Color.FromArgb( v, v, v ));
		}
	}
	BeginInvoke( onGrayscaleComplete, new object[] { this, EventArgs.Empty } );
 }  

 onGrayscaleComplete = new EventHandler( OnGrayscaleComplete );

 if ( pictureBox.Image != null ) {
	bmpToGrayscale = new Bitmap( pictureBox.Image );
	grayscaleMenuItem.Enabled = false;
	Thread thread = new Thread( new ThreadStart( ThreadProc ));
	thread.Start();
 }