11 - WinForms - CustomControl, Drawing.md

Windows Forms – Custom Controls, Drawing

• 1. Objectives
• 2. Extended Controls
• 3. Composite Controls
• 4. Custom Controls + Drawing
• 5. Bibliography

1. Objectives

• understanding the concept of custom control;
• understanding the differences between extended controls, composite controls and custom controls;
• creating a custom control and using it in a different project;
• drawing shapes and text on a windows forms control / form;

2. Extended Controls

Full source code available, check the NumericTextBoxControlSample sample

How to: Inherit from Existing Windows Forms Controls: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/how-to-inherit-from-existing-windows-forms-controls

3. Composite Controls

Full source code available, check the NumericTextBoxControlSample sample

How to: Inherit from the UserControl Class: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/how-to-inherit-from-the-usercontrol-class

4. Custom Controls + Drawing

The Graphics class provides methods for drawing objects to the display device.

Activity

Full source code available, check the BarChartGraphicsSample sample

1. Create a new project of the type "Class Library (.NET Framework)" (recommended) or "Windows Forms Control Library (.NET Framework)" with the name "ChartLibrary"

2. Add a new class BarChartValue, defined as follows:

   public class BarChartValue
   {
   	public string Label { get; set; }
   	public float Value { get; set; }
   
   	public BarChartValue(string label, float value)
   	{
   		Label = label;
   		Value = value;
   	}
   }

3. Add a new "Custom Control (Windows Forms)" and name it BarChartControl

4. Add the Data property in the BarChartControl class

   private BarChartValue[] _data;
   public BarChartValue[] Data
   {
   	get { return _data; }
   	set { _data = value; }
   }

5. Modify the constructor of the BarChartControl class as follows:

   public BarChartControl()
   {
   	InitializeComponent();
   
   	//redraws the chart if the control is resized
   	ResizeRedraw = true;
   
   	//default data
   	Data = new[]
   	{
   		new BarChartValue("2015", 30), 
   		new BarChartValue("2016", 80),
   		new BarChartValue("2017", 40)
   	};
   }

6. Handle the Paint event for the BarChartControl as follows:

   private void BarChartControl_Paint(object sender, PaintEventArgs e)
   {
   	//get the drawing context
   	Graphics graphics = e.Graphics;
   	//get the drawing area
   	Rectangle clipRectangle = e.ClipRectangle;
   
   	//determine the width of the bars
   	var barWidth = clipRectangle.Width / Data.Length;
   	//compute the maximum bar height
   	var maxBarHeight = clipRectangle.Height * 0.9;
   	//compute the scaling factor based on the maximum value that we want to represent
   	var scalingFactor = maxBarHeight / Data.Max(x=>x.Value);
   
   	Brush redBrush = new SolidBrush(Color.Red);
   
   	for (int i = 0; i < Data.Length; i++)
   	{
   		var barHeight = Data[i].Value * scalingFactor;
   
   		graphics.FillRectangle(
   			redBrush, 
   			i * barWidth, 
   			(float) (clipRectangle.Height - barHeight), 
   			(float) (0.8 * barWidth), 
   			(float) barHeight);
   	}
   }	

7. Add a new Windows Forms project called "BarChartGraphicsSample"

8. Add a reference to the ClassLibrary project created earlier

9. From the ToolBox drag a 'BarChartControl' to the default form in the project

Assignments (for you to try) 🎮

1. Display on each bar the Label and Value properties of the corresponding BarChartValue object.

Activity

Full source code available, check the PieChartGraphicsSample sample

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

2. Add a new class “PieChartCategory”, defined as follows:

   internal class PieChartCategory
   {
   	public string Description { get; set; }
   	
   	public float Percentage { get; set; }
   	
   	public Color Color { get; set; }
   	
   	public PieChartCategory(string description, float percent, Color color)
   	{
   		Description = description;
   		Percentage = percent;
   		Color = color;
   	}
   }

3. Add a new "Custom Control (Windows Forms)" and name it “PieChartControl”
   

4. Add the “Data “ property in the “PieChartControl” class

   private PieChartCategory[] _data;
   public PieChartCategory[] Data {
   	get { return _data; }
   	set
   	{
   		if(_data == value)
   			return;
   
   		_data = value;
   		
   		//trigger the Paint event
   		Invalidate();
   	}
   }

5. Modify the constructor of the “PieChartControl” class as follows:

   public PieChartControl()
   {
   	InitializeComponent();
   
   	//redraws if resized
   	ResizeRedraw = true;
   	
   	//Default data
   	Data = new[]
   	{
   		new PieChartCategory("Category 1", 20, Color.Red),
   		new PieChartCategory("Category 2", 80, Color.Blue)
   	};
   }

6. Handle the “Paint” event for the “PieChartControl” as follows:

   private void PieChartControl_Paint(object sender, PaintEventArgs e)
   {
   	//width reserved for displaying the legend
   	int legendWidth = 150;
   	
   	//get the drawing context
   	Graphics graphics = e.Graphics;
   	//get the drqwing area
   	Rectangle clipRectangle = e.ClipRectangle;
   	
   	//compute the maximum radius
   	float radius = Math.Min(clipRectangle.Height, clipRectangle.Width - legendWidth) / (float)2;
   	
   	//determine the center of the pie
   	int xCenter = (clipRectangle.Width - legendWidth) / 2;
   	int yCenter = clipRectangle.Height / 2;
   	
   	//determine the x and y coordinate of the pie
   	float x = xCenter - radius;
   	float y = yCenter - radius;
   	
   	//determine the width and the height
   	float width = radius * 2;
   	float height = radius * 2;
   	
   	//draw the pie sectors
   	float percent1 = 0;
   	float percent2 = 0;
   	for (int i = 0; i < Data.Length; i++)
   	{
   		if (i >= 1)
   			percent1 += Data[i - 1].Percentage;
   			
   		percent2 += Data[i].Percentage;
   		
   		float angle1 = percent1 / 100 * 360;
   		float angle2 = percent2 / 100 * 360;
   		
   		Brush b = new SolidBrush(Data[i].Color);
   		
   		graphics.FillPie(b, x, y, width, height, angle1, angle2 - angle1);
   	}
   	
   	//draw the pie contour
   	Pen pen = new Pen(Color.Black);
   	graphics.DrawEllipse(pen, x, y, width, height);
   	
   	//draw the chart legend
   	float xpos = x + width + 20;
   	float ypos = y;
   	for (int i = 0; i < Data.Length; i++)
   	{
   		Brush b = new SolidBrush(Data[i].Color);
   		graphics.FillRectangle(b, xpos, ypos, 30, 30);
   		graphics.DrawRectangle(pen, xpos, ypos, 30, 30);
   		Brush b2 = new SolidBrush(Color.Black);
   		graphics.DrawString(Data[i].Description + ": " + Data[i].Percentage + "%",
   		Font, b2,
   		xpos + 35, ypos + 12);
   		ypos += 35;
   	}
   }

7. Add the “PieChartControl” to the “MainForm” (using the Toolbox)

8. Handle the “Load” event for the “MainForm” as follows:

   private void MainForm_Load(object sender, System.EventArgs e)
   {
   	PieChartCategory[] pieCategories = {
   		new PieChartCategory("Gold", 20, Color.Red),
   		new PieChartCategory("Stocks", 15, Color.Blue),
   		new PieChartCategory("Bonds", 35, Color.Magenta),
   		new PieChartCategory("ETFs", 15, Color.YellowGreen),
   		new PieChartCategory("Options", (float) 7.5, Color.Tomato),
   		new PieChartCategory("Cash", (float) 7.5, Color.Beige)
   	};
   	
   	pieChartControl1.Data = pieCategories;
   }

Activity

Full source code available, check the ClockControlSample and ClockControlAppSample samples

5. Bibliography

• Windows Forms Control Development Basics: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/windows-forms-control-development-basics
• How to: Inherit from Existing Windows Forms Controls: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/how-to-inherit-from-existing-windows-forms-controls
• How to: Inherit from the UserControl Class: https://docs.microsoft.com/en-us/dotnet/framework/winforms/controls/how-to-inherit-from-the-usercontrol-class