Building Windows Applications

Configuring Your Form for Resizing

Every time I built a resizable form in Visual Basic 6.0 (which includes every form I built except for the simplest of dialog boxes), I had to write code into the form's Resize event.

I had to decide how I wanted each control to adjust to the new size of the form, what size was too small for my interface to be usable, and I had to remember to check if the form had been minimized before trying to do any resizing. This code was not particularly hard to write, and after 50 or 60 forms I could do it without much thought, but it still took time and effort for every form I created. In Windows forms, a variety of features have come together to allow you to configure your controls for auto-resizing without having to write a single line of code. By combining the docking and anchoring features with the careful use of panels, you can set your form up to resize in almost any way you can imagine. If you add in the auto-scroll feature, you can even have parts of the form that do not resize at all, but instead extend right off the visible area of the form.

Using Docking to Handle Resizing

Docking windows and toolbars have been in use for quite some time, so the general concept is not new; a docked item is attached to one of the edges of its container (such as a form). Consider a form that contains only a single ListBox control. If you set the ListBox 's Dock property to Left (see Figure 3.5), the height of the control will be fixed to the height of the form's client area (causing the list box to fill the form from top to bottom), while the position of the control will be locked to the left side of the form. The only thing you can change about the size of the list box at this point is its width, controlling how far out from the left side it extends. Docking to the right is essentially the same; the list box becomes attached to the right side of the form, but you can still change its width as desired. Docking to the top or bottom will cause the width to be fixed to fill the width of the form, but the height of the control can still be modified.


Docking a control to the left makes it stick to the left side, while filling the vertical space of the container

Figure 3.5

Docking a control to the left makes it stick to the left side, while filling the vertical space of the container.

In addition to docking to one of the four sides, controls also support a fifth (sixth if you count None for no docking) docking setting, Fill . If you set the Dock property to Fill , that control becomes attached to all four sides of the container, adjusting itself automatically as the form is resized. You cannot adjust any size or position settings for a control that has been docked to fill the container.

Remember that you are docking the control to its container, which in this example is the Form , but could be a container control such as a GroupBox or Panel . This flexibility leads to more layout options, as you will see later in the section on "Using Panels."

The container (form, panel, or other type of container control) has a DockPadding property, which allows it to specify a certain amount of padding between it and docked controls. The padding values can be specified individually for the four sides of the container, or an overall padding value that applies to all of the sides at once. If a container has specified a DockPadding value of 10, for example, a control docked to the left will be positioned 10 pixels away from the left edge. The DockPadding setting is great for creating a more visually pleasing user interface as it results in a border around the form while still enabling the automatic resizing of docked controls (see Figure 3.6 ).

DockPadding allows you to dock, without sacrificing a bit of white space around the edge of your controls.

Figure 3.6
DockPadding allows you to dock, without sacrificing a bit of white space around the edge of your controls.

Docking gets a little more complicated when multiple docked controls are involved. If you dock more than one control to the same edge, the second control will dock alongside the first instead of directly to the container. Going back to the example with the ListBox on a form, you can try multiple docked controls to see what happens. If you docked the ListBox to the bottom and then added a new DataGrid to the form, setting its Dock property also to Bottom , you would have produced an interface similar to Figure 3.7, where the ListBox appears below the DataGrid.

Multiple controls docked to the same side will stack instead of overlap.

Figure 3.7
Multiple controls docked to the same side will stack instead of overlap.

Both of the controls are docked to the form and will resize as the form is resized. If you have controls docked to one or more sides of your container, and then you set another control's Dock property to Fill , the control set to Fill will be automatically sized to use all of the remaining area of the container. If you have multiple controls docked on a form, you might want to use the Splitter control. Splitter is a special Windows Forms control that, when docked between two other controls, allows you to resize the two controls at runtime. Using the Splitter control and a few other key controls, you can create a standard Explorer view form in a matter of minutes.

To add a splitter to your form, you need to be careful of the order in which you add your controls. Try adding a ListBox to an empty form, and docking it to the left. Then add a splitter control, and dock it to the left as well (it is by default). Finally, add a DataGrid control, dock it to the left as well, or set its dock property to Fill , and you will have a working example of using a splitter!

A little confusing? It can appear very complex, but the best bet is to try it out on your own, adding a variety of controls to a blank form and playing around with the various Dock / DockPadding settings.

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