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Föreläsning 18

Händelser (events)

Event med handler

1. public MyForm() {
2. Button button = new Button {
3. Text = "Click Me"
4. };
5. Controls.Add(button);
6. button.Click += ClickedEventHandler;
7. }
9. private void ClickedEventHandler(object sender, EventArgs e) {
10. MessageBox.Show("You clicked the button");
11. }

Event med handler och tillstånd

1. private int clickCount;
3. public MyForm() {
4. Button button = new Button {
5. Text = "Click Me"
6. };
7. Controls.Add(button);
8. button.Click += ClickedEventHandler;
9. }
11. private void ClickedEventHandler(object sender, EventArgs e) {
12. clickCount += 1;
13. MessageBox.Show("Times clicked: " + clickCount);
14. }

Flera handlers

1. public MyForm() {
2. TableLayoutPanel table = new TableLayoutPanel {
3. RowCount = 2
4. };
5. Controls.Add(table);
6. Button left = new Button {
7. Text = "Left"
8. };
9. left.Click += LeftClickedEventHandler;
10. table.Controls.Add(left);
12. Button right = new Button {
13. Text = "Right"
14. };
15. right.Click += RightClickedEventHandler;
16. table.Controls.Add(right);
17. }
19. private void LeftClickedEventHandler(object sender, EventArgs e) {
20. MessageBox.Show("You clicked: Left");
21. }
23. private void RightClickedEventHandler(object sender, EventArgs e) {
24. MessageBox.Show("You clicked: Right");
25. }

En enda handler med sender

1. public MyForm() {
2. TableLayoutPanel table = new TableLayoutPanel {
3. ColumnCount = 2
4. };
5. Controls.Add(table);
6. Button left = new Button {
7. Text = "Left"
8. };
9. left.Click += ClickedEventHandler;
10. table.Controls.Add(left);
12. Button right = new Button {
13. Text = "Right"
14. };
15. right.Click += ClickedEventHandler;
16. table.Controls.Add(right);
17. }
19. private void ClickedEventHandler(object sender, EventArgs e) {
20. Button button = (Button) sender;
21. MessageBox.Show("You clicked: " + button.Text);
22. }

Event: TextChanged

1. private TextBox textBox;
2. private Label label;
4. public MyForm() {
5. TableLayoutPanel table = new TableLayoutPanel {
6. RowCount = 2
7. };
8. Controls.Add(table);
10. textBox = new TextBox();
11. table.Controls.Add(textBox);
12. textBox.TextChanged += TextBoxChangedEventHandler;
14. label = new Label {
15. Text = "Length: 0"
16. };
17. table.Controls.Add(label);
18. }
20. private void TextBoxChangedEventHandler(object sender, EventArgs e) {
21. label.Text = "Length: " + textBox.Text.Length;
22. }

Event: SelectedIndexChanged

1. private ComboBox comboBox;
3. public MyForm() {
4. comboBox = new ComboBox {
5. DropDownStyle = ComboBoxStyle.DropDownList
6. };
7. Controls.Add(comboBox);
8. comboBox.Items.Add("Game of Thrones");
9. comboBox.Items.Add("Stranger Things");
10. comboBox.Items.Add("The Walking Dead");
11. comboBox.SelectedIndexChanged += ChangedEventHandler;
12. }
14. private void ChangedEventHandler(object sender, EventArgs e) {
15. MessageBox.Show(
16. "You have selected index " +
17. comboBox.SelectedIndex + ": " +
18. comboBox.SelectedItem
19. );
20. }