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.FIGURE 4.13.TheComponent Selector list.The Properties PageThe Properties page of the Object Inspector displays all the design-time propertiesfor the currently selected control.The Properties page has two columns: The Propertycolumn is on the left side of the Properties page and shows the property name; theValue column is on the right side of the Properties page and is where you type orselect the value for the property.If the selected component has more properties than will fit in the Object Inspector,a scrollbar will be provided so that you can scroll up or down to locate other properties.NOTE: If you have multiple components selected on the form, the ObjectInspector shows all the properties that those components have in common.You canuse this feature to modify the properties of several components at one time.Forexample, to change the width of several components at one time, you can select allthe components and then modify the Width property in the Object Inspector.When youpress Enter or move to another property, all the components you selected will havetheir Width property modified.Figure 4.14 shows the Object Inspector when a Memo component is selected.FIGURE 4.14.TheObject Inspector showing Memo component properties.Properties can be integer values, enumerations, sets, other objects, strings,and other types.(Properties are discussed in detail tomorrow.) The Object Inspectordeals with each type of property according to the data type of the property.Delphihas several built-in property editors to handle data input for the property.Forexample, the Top property accepts an Integer value.Because the Integer type is abasic data type, no special handling is required, so the property editor is fairlybasic.The property editor for this type of property enables you to type a valuedirectly in the Value column for integer properties such as Top, Left, Width, andHeight.NOTE: In most cases, the property editor does parameter checking for anyproperties in which you can enter an integer value.The Width property, for example,cannot be a negative number.If you attempt to enter a negative number for the Widthof a control, Delphi will force the width to the minimum allowed for that control(usually 0).If you enter a string value for a property that expects an integer value,Delphi will display an error message.It is the job of the property editor to doparameter checking.In many cases, the property editor for the property contains a list of items fromwhich you can choose.Properties that have an enumeration or Boolean value as theirbase data type fall into this category.When you click the Value column with thistype of property editor, you will see a drop-down button on the right side of theValue column.Clicking this button displays the list of possible values.TIP: If you double-click the Value column for this type of property, theproperty editor will cycle through the possible choices.To quickly change a Booleanproperty, for example, simply double-click its value.Because the only choices areTrue and False, double-clicking the value has the effect of toggling the property'svalue.If you look closely at the Object Inspector, you will see that some propertieshave a plus sign preceding their names.Properties that are sets and properties thatare classes both have the plus sign in front of their names.The plus sign indicatesthat the property node can be expanded to show the set or, in the case of propertiesthat are classes, the properties of that class.To expand a node, double-click onthe Property column for that property (on the property name) or choose Expand fromthe Object Inspector context menu.To collapse the node, double-click it again orchoose Collapse from the Object Inspector context menu.To see an example of a set property, choose a form and then double-click the BorderIconsproperty in the Object Inspector.The node expands and you see four members of theset.You can turn on or off any of the four members as needed.In the case of properties that are objects (instances of a VCL class), you havetwo choices in editing the property.First, you can click the Value column for theproperty and then click the button to the right side of the value (if one exists).This button is indicated by an ellipsis (.) on its face.Clicking this button invokesthe property editor for that particular control.For example, click the Font propertyand then click the ellipsis button.The Choose Font dialog box is displayed so thatyou can select the font.The second way you can edit this type of property is by expanding the property node [ Pobierz całość w formacie PDF ]
