Đối tượng - Một mảnh rời rạc của dữ liệu được định nghĩa bởi một lớp học, bao gồm các yếu tố công cộng và các tài sản dữ liệu nội bộ - Một yếu tố mô tả của một đối tượng. Tài sản được định nghĩa trong lớp và thường mô tả các đối tượng trong một cách nào đó. | What the User Sees CheckBox The CheckBox control is normally used to display options that can be turned on and off. You can change the label by setting the Text property and control whether it is checked or not using the Checkstate property. The Checkstate property has a third possible value Indeterminate. This is normally used when the program cannot give a definitive yes or no answer. An example of this might be when the CheckBox has a number of other fields below it some of which are checked and some of which are unchecked the sample form in Figure 4-4 shows how this can work . Figure 4-4 RadioButton RadioButton controls are sometimes known as option buttons. They represent a set of information whereby only one option can be chosen. Each option is displayed as a separate radio button and users click one to select it. When one radio button is selected all other radio buttons are deselected automatically. Because RadioButton controls are automatically grouped in this fashion it s common to keep them in a layout container control such as a GroupBox or Panel so they don t affect other options groups. To achieve the separate color and clothes selections shown in Figure 4-5 two Panel controls were first placed on the form and then the RadioButton controls were added to the Panels. Figure 4-5 ComboBox When you have a large number of options from which to choose RadioButton controls may get a little messy. Or if you have limited space on the form it may be impossible to position the RadioButton controls so they re usable. ComboBox controls can be used to avoid both problems. A ComboBox stores a list of information from which users can choose. To display the list they click the drop-down button in the form of a downward pointing arrow and once they ve selected an option it is displayed in a TextBox. 57 Chapter 4 ListBox An alternative to the ComboBox for presenting a lot of information is the ListBox. The ListBox can be sized and positioned so that users can see many .
