.NET Table 4.3 StatusBarPanel class

The StatusBarPanel class is a component that appears as a panel within a StatusBar control. This class is part of the System.Windows.Forms namespace, and inherits from the System.ComponentModel.Component class. A panel must be associated with a StatusBar instance with its ShowPanels property set to true in order to appear on a form.

4.3.2ASSIGNING PANEL TEXT

With our panels defined, we simply set the Text property value for each panel to have the text displayed by the application. This only works for panels with their

Style property set to Text, of course. We will look at our owner-drawn panel in section 4.4. Since our panels only have meaning after an image is loaded, we assign their values as part of the Click event handler for the Load button, as indicated by the following steps.

SET THE TEXT TO APPEAR IN THE PANELS

SET THE TEXT TO APPEAR IN THE PANELS (continued)

Two items are worth noting in this code:

bThe ShowPanels property is set to false while an image is loading so that the StatusBar.Text property setting will appear, and set to true after the image is loaded and the panels are set.

cThe Format method used here is a static method provided by the String class for constructing a string. We could spend a chapter covering this and other features available in C# strings generally and the .NET System.String class specifically, but instead will assume you can look this one up in the documentation. In the code shown here, the "{0:#} x {1:#}" string indicates that two parameters are required, both of them integers.

Build and run the application to see these panels in action. Resize the window to see how the panels react. You will notice that the first panel resizes automatically along with the window, while the second two panels maintain their initial size. This is consistent with the AutoSize settings we used for these objects.

4.4OWNER-DRAWN PANELS

So what about this owner-drawn panel? Text panels do not need to worry about drawing their text onto the panel, as the .NET Framework handles this internally. There are some cases where text just will not do, and these situations requiring manual drawing of the panel.

Drawing of panels and other objects in .NET are handled through use of the System.Drawing namespace, sometimes referred to as GDI+ since it is based on an update to the graphical drawing interface provided by Microsoft. Components such as menus, status bars, and tabs that contain drawable components support a DrawItem event that occurs when an item in the component should be drawn. Controls derived from the Control class provide a Paint event for this purpose. Both types of drawing make use of the Graphics class discussed in this section in order to draw the item.

This section will examine how owner-drawn status bar panels are supported, and draw the sbpnlImagePercent panel for our application. A similar discussion would apply to owner-drawn menu items or other objects supporting the DrawItem event. The result of our changes is shown in figure 4.5.

Figure 4.5

The third status bar panel here indicates that 30 percent of the image is visible in the window.

As you can see in the figure, when the image is displayed in Actual Size mode, the third panel will show a numeric and visual representation of how much of the image is displayed. Before we draw this panel, let’s take a closer look at the DrawItem event.

4.4.1THE DRAWITEM EVENT

The DrawItem event is used by a number of classes to draw an item contained within some sort of larger collection. For instance, the MenuItem, ListBox, and ComboBox classes all include a DrawItem event for custom drawing of their contents. These classes use the DrawItemEventArgs class to provide the data associated with the event. The StatusBar class uses a derived version of this class, but the bulk of the drawing information is in the base class. An overview of this base class is provided in .NET Table 4.4.

.NET Table 4.4 DrawItemEventArgs class

The DrawItemEventArgs class is an event object used when handling DrawItem events in a number of classes. This class is part of the System.Windows.Forms namespace, and inherits from the System.EventArgs class. Practically, this class is used to manually draw list box items, menu items, status bar panels and other objects.

The StatusBarDrawItemEventArgs class extends this class for use with StatusBar objects. This class includes a public Panel property to indicate which panel requires drawing.

For the StatusBar class, the StatusBarDrawItemEventArgs class derives from the DrawItemEventArgs class and is received by StatusBar.DrawItem event handlers. The Panel property provided by this class is useful both for identifying the panel and when the text assigned to the panel is needed.

When a DrawItem event handler is invoked, the default property values are what you might expect. The Bounds property is set to the display rectangle of the panel to draw. This rectangle is with respect to the rectangle for the containing status bar, so the upper left corner of a panel’s bounds is not (0,0). The Font and ForeColor properties are set to the font information for the StatusBar object; the Graphics property to an appropriate drawing object, the Index to the zero-based index number of the panel, and State is typically set to DrawItemState.None. The DrawItem event is called once for each panel drawn.

.NET Table 4.5 System.Drawing namespace

The System.Drawing namespace provides access to basic graphics functionality provided by the graphical device interface (GDI+). The classes in this namespace are used when drawing to any display device such as a screen or printer, and to represent drawing primitives such as rectangles and points.