第 7 章 列表、循环和打印

1. 第7章 列表、循环和打印

2. 列表框和组合框 提供一列表项，用户做出选择 C#自动添加滚动条 DropDownStyle属性，供用户输入 组合框text属性，设计可以删除； 列表框text属性，只能运行时访问 简单列表框、简单组合框、下拉组合框、下拉列表框

3. Combox的DropDownStyle属性

4. Items集合 Items.Add Items.Insert 显示在列表框中得表项集合，Items[1]索引从0开始。 填充列表：设计或运行期间

6. Using the Items.Insert Method • Choose location for new item added to list • Items.Insert method • Specify index position for new item • An existing position or end of list • Index position is zero based • First position, use index position = 0 • Inserting an item beyond end of list throws an exception • Do not set list control’s Sorted property to true

7. Items.Add方法 • 通用方式 • 使用Items.Add方法示例 • 添加文本框内容 Object.Items.Add(ItemValue); schoolsListBox.Items.Add("Harvard"); schoolsListBox.Items.Add("Stanford"); schoolsListBox.Items.Add(schoolsTextBox.Text); majorsComboBox.Items.Add(majorsComboBox.Text); majorsComboBox.Items.Add(majorString); coffeeComboBox.Items.Add(coffeeComboBox.Text); schoolsListBox.Items.Add(schoolTextBox.Text);

8. Items.Insert方法 索引位置 Object.Items.Insert(IndexPosition, ItemValue); schoolsListBox.Items.Insert(0, "Harvard"); majorsComboBox.Items.Insert(1, majorsComboBox.Text); 要使用Insert方法选择索引位置，不能把列表框的Sorted属性设置为true • 通式 • 方法实例

9. SelectedIndex属性 突出显示 -1没有任何选项被选定 • 该表项索引编号被存储在SelectedIndex属性中 // Select the fourth item in list. coffeeTypesListBox.SelectedIndex = 3; // Deselect all items in list. coffeeTypesListBox.SelectedIndex = -1;

10. Items.Count属性 表项数量 示例 totalItemsInteger= itemsListBox.Items.Count; MessageBox.Show(“The number of items in the list is ” + itemsListBox.Items.Count.ToString()); • 总是比最高SelectedIndex大1，下标从0开始 • 例如: 5个表项 • Items.Count = 5 • Highest index = 4 • 可能的SelectedIndex= 0, 1, 2, 3, 4

11. Referencing the Items Collection - 2 引用当前列表元素，结合使用Items属性和the SelectedIndex属性 selectedFlavorString= flavorListBox.Items[flavorListBox.SelectedIndex].ToString(); 通过引用控件 Text 属性获取选定表项selectedMajorLabel.Text = majorsComboBox.Text; 给特定表项赋值替换以前内容schoolsListBox.Items[0] = “My School”;

12. Removing an Item from a List • Items.RemoveAt method • Removes an item by index • First list element is 0, last element is Items.Count -1 • An invalid index will cause an IndexOutOfRange exception namesListBox.Items.RemoveAt[0]; schoolsComboBox.Items.RemoveAt[indexInteger]; coffeeComboBox.Items.RemoveAt(coffeeComboBox.SelectedIndex); • Items.Remove method • Looks for the specified string, removes item if string found • No exception is generated if the item is not found namesListBox.Items.Remove[“My School”]; schoolsComboBox.Items.Remove(schoolTextBox.Text); coffeeComboBox.Items.Remove(coffeeComboBox.Text);

13. 从列表中删除表项 • Items.RemoveAt方法 • 通过下标删除 • 首0, 末尾Items.Count-1 namesListBox.Items.RemoveAt[0]; schoolsComboBox.Items.RemoveAt[indexInteger]; coffeeComboBox.Items.RemoveAt(coffeeComboBox.SelectedIndex); • Items.Remove方法 • 集合中寻找制定字符串 • 找不到也不会抛出异常 namesListBox.Items.Remove[“My School”]; schoolsComboBox.Items.Remove(schoolTextBox.Text); coffeeComboBox.Items.Remove(coffeeComboBox.Text);

14. 清除列表 // Confirm clearing the majors list. DialogResult responseDialogResult; responseDialogResult = MessageBox.Show("Clear the majors list?", "Clear Majors List", MessageBoxButtons.YesNo, MessageBoxIcon.Question); if (responseDialogResult == DialogResult.Yes) { majorsComboBox.Items.Clear(); } Items.Clear方法 删除列表中的全部选项

15. 列表框和组合框的事件 • SelectedIndexChanged事件 • Occurs when the user makes a selection from a list • TextChanged事件 • Each keystroke generates a TextChanged event • Available in combo boxes not list boxes • Enter 事件 • Occurs when a control receives the focus • Use to make existing text appear selected • Leave 事件 • Fires when a control loses focus • Often used for validating input data

16. While和do/While循环 循环体至少执行1次 do { //Statement in loop } While(condition); While(condition) { //Statement in loop } totalInteger = 0; while (totalInteger != 0) { // Statements in loop (will never be done). } 基于指定的条件终止，当条件为true时，循环语句继续执行，一般事先不知道循环次数,通式

17. The while and do/while Loops - 3 • do/while loop • Tests for completion at bottom of loop • Also called a posttest or exit test • Statements inside loop will always execute at least once

18. 使用bool变量3步 bool itemFoundBoolean = false; while (! itemFoundBoolean) // Loop when condition is false (not true). { // Statement(s) in loop. // Must include a statement that sets itemFoundBoolean to true. } 首先声明一个变量，设置初值 当某种情况出现，把这个变量的值设为true 循环条件判断变量是否为true

19. For循环 for (intindexInteger = 2; indexInteger <= 100; indexInteger += 2) for (countInteger = startInteger; countInteger < endInteger;countInteger += incrementInteger) for (intcountInteger = 0; countInteger <= coffeeTypeComboBox.Items.Count – 1;countInteger++) for (rateDecimal = 0.05M; rateDecimal < 0.25M; rateDecimal += 0.05M) for (intcountDownInteger = 10; countDownInteger > 0; countDownInteger– –) 初始化、条件、迭代后发生的动作

20. 退出循环 Break Continue：将控制权传递到循环的最后，然后重新测试循环退出条件。将循环跳到下一次迭代上。

21. drawString方法：向图形页面发送一行文本 private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e) { e.Graphics.DrawString("沈群力", new Font("Arial", 36), Brushes.Black, 100, 100); }

22. ①事件处理方法的顶部，定义字体、行高以及X和Y的坐标①事件处理方法的顶部，定义字体、行高以及X和Y的坐标 ②设置打印的行 ③打印行 ④如果想打印另一行，则使Y坐标递增 ⑤如果要打印多行，则把②③④放入循环中

23. 打印预览 PrintPreviewDialog