1 Working with Controls at Run Time

2 Objectives You will be able to Add controls to a Windows form at run time. Modify controls at run time.

3 Setting Up Controls at Run Time Why do this? May not know exactly what we need at design time. With a large number of controls, it might be easier to write code to set up the controls than to create them manually at design time.

4 The Controls Collection The Windows Form class has a Controls collection. Everything that we see on the form. Implements interface IList Accessible at run time as the form's Controls property. We can instantiate control objects and add them to the collection. Also modify existing controls.

5 Example: The Game of Chomp The game of Chomp was described in a Math Trek column in Science News: title/Math_Trek__Chomping_to_Win title/Math_Trek__Chomping_to_Win

6 The Game of Chomp

8 Implementing Chomp Let's create a Windows Form for a game of chomp with five rows and six columns of squares. Each square will be a button. When a button is clicked, it and all buttons above it and to its right will disappear. Create all buttons at run time. Modify them at run time as users play.

9 Getting Started Create a new C# Windows Forms project

10 An Example Button We can copy from Visual Studio's generated code.

11 An Example Button Double click on the button to add an event handler.

12 Generated Code Note statement to hook up the Event Handler. (line 43)

13 Form1 public partial class Form1 : Form { int number_of_rows = 5; int number_of_cols = 6; int button_size = 50;

14 Add_Button() Add to class Form private void Add_Button(int row, int col) { Button btn = new Button(); btn.BackColor = System.Drawing.Color.Blue; btn.Location = new System.Drawing.Point(col*button_size, row*button_size); btn.Name = "btn" + row + col; btn.Size = new System.Drawing.Size(button_size, button_size); btn.UseVisualStyleBackColor = false; btn.Click += new System.EventHandler(btn00_Click); Controls.Add(btn); } Delete the example button.

15 Form Load Event Handler

16 Form1_Load() private void Form1_Load(object sender, EventArgs e) { for (int row = 0; row < number_of_rows; ++row) { for (int col = 0; col < number_of_cols; ++col) { Add_Button(row, col); }

17 Program Running

18 Set up the "poisoned" button private void Add_Button(int row, int col) { Button btn = new Button(); if ((row == number_of_rows - 1) && (col == 0)) { btn.BackColor = System.Drawing.Color.Red; btn.Enabled = false; } else { btn.BackColor = System.Drawing.Color.Blue; btn.Enabled = true; }

19 Form with Poisoned Button

20 Initial Click Handler private void btn00_Click(object sender, EventArgs e) { Button btn = (Button)sender; int row = btn.Name[3] - '0'; int col = btn.Name[4] - '0'; MessageBox.Show("Row " + row + " Col " + col + " clicked"); }

21 Click Lower Right Corner

22 Update_Buttons private void Update_Buttons(int row, int col) { for (int i = 0; i < Controls.Count; ++i) { Control c = Controls[i]; Button btn = c as Button; if (btn == null) continue; int btn_row = btn.Name[3] - '0'; int btn_col = btn.Name[4] - '0'; if ((btn_row = col)) { btn.BackColor = Color.White; btn.Enabled = false; } Note "as"

23 Update_Buttons private void btn00_Click(object sender, EventArgs e) { Button btn = (Button)sender; int row = btn.Name[3] - '0'; int col = btn.Name[4] - '0'; //MessageBox.Show("Row " + row + " Col " + col + " clicked"); Update_Buttons(row, col); }

24 Keep track of the players public partial class Form1 : Form { int current_player = 1;... private void Form1_Load(object sender, EventArgs e) { for (int row = 0; row < number_of_rows; row++) { for (int col = 0; col < number_of_cols; col++) { Add_Button(row, col); } MessageBox.Show("Player 1 "); }

25 Keep track of the players private void btn00_Click(object sender, EventArgs e) { Button btn = (Button)sender; int row = btn.Name[3] - '0'; int col = btn.Name[4] - '0'; //MessageBox.Show("Row " + row + " Col " + col + " clicked"); Update_Buttons(row, col); current_player = current_player == 1? 2 : 1; MessageBox.Show("Player " + current_player); } Build and run

26 Initial Form

27 Check for Game Over private bool Game_Over() { for (int i = 0; i < Controls.Count; ++i) { Control c = Controls[i]; Button btn = c as Button; if (btn == null) continue; if (btn.Enabled) { return false; } return true; }

28 Check for Game Over private void btn00_Click(object sender, EventArgs e) { Button btn = (Button)sender; int row = btn.Name[3] - '0'; int col = btn.Name[4] - '0'; //MessageBox.Show("Row " + row + " Col " + col + " clicked"); Update_Buttons(row, col); if (Game_Over() ) { MessageBox.Show("Game Over! \n" + "Player " + current_player + " wins."); } else { current_player = current_player == 1? 2 : 1; MessageBox.Show("Player " + current_player); }