Visual Basic Concepts

Positioning HTML Elements

After you add elements to your page, you may want to rearrange and fine-tune their positioning. There are several things you should know about positioning elements on the page:

• Move text elements with the keyboard. Text elements such as headings, paragraphs, and labels are positioned independently of other elements on the page. You can move text elements by using the ENTER or BACKSPACE keys. Moving a text element in this way does not affect the other elements around it — that is, all of the text elements on your page will move down a line if you press ENTER at the top of the page, but buttons and other visual elements will not be moved.

  Tip   You can also move align text elements using the toolbar alignment icons.

• Move nontext elements with the mouse. You can move elements such as buttons, images, and check boxes by clicking on them, selecting the gray border around the element, and moving the element to its new location.

  Note   You must select the border of an element in order to move or delete it. When you select the body of an element, the border shows a series of diagonal lines. When you select the border of an element, the border shows gray fill. You can move an element when the gray fill is visible.

• Elements without a run-time interface cannot be repositioned once they are added to the page. Some Visual Basic controls, such as the common dialog or the sysinfo control are invisible at run time. If you add one of these to the page, you cannot select it or reposition it. You can delete the item by selecting it from the treeview and using the shortcut menu option to remove it.
  
  
• Elements in an HTML page can be layered. In addition to arranging your elements on the page in two-dimensional space, you can layer elements on top of and behind each other by using the Order toolbar options.
  
  
• There are two positioning modes: absolute and relative. These modes determine how the system interprets your actions as you add elements to the page. It is important to understand the ramifications of choosing between these two modes.

Absolute and Relative Positioning

When you are designing or editing pages in the designer window, you can work in one of two modes: absolute mode or relative mode:

• In absolute positioning mode, all items you drag onto or move on the page are placed at the exact location where you release the cursor. Visual Basic writes information to the HTML for each element that indicates the exact position of the item.
  
  
• In relative positioning mode, each new item you drag onto the screen is placed in the next available cursor position. If you have not used the cursor to add any paragraph <P> tags to the page, the elements you drop on the page are positioned in the next available space, moving left to right across the screen, regardless of where you drop the element on the page.

The following screen shows how Visual Basic positions three buttons that are dropped at varying locations on the drawing surface in absolute mode:

Buttons Positioned in Absolute Mode

If you were not working in absolute mode and dropped those three buttons onto the screen, they would be positioned as shown in the following screen:

Buttons Positioned in Relative Mode

Absolute and relative mode have advantages and disadvantages. Absolute mode allows you finer control over the layout of your page but is not as flexible as relative positioning. With relative positioning, the page can easily adjust to end users with different viewing environments. For example, if the browser screen is small or the computer's resolution is much lower than that on the development machine, only a portion of your absolutely positioned page may appear to the end user. In relative positioning, the page would dynamically wrap its elements and adjust to the browser's screen space.

To change from absolute mode to relative mode, you select or deselect the Absolute Positioning icon on the toolbar. This sets the mode for the entire page.

Note   You can also turn on Absolute Positioning for select items on the page, rather than the whole page itself, by using the Absolute Positioning toolbar icon. Selecting this button affects both the selected element and all subsequently created elements on the page unless you deselect it. It does not affect elements already placed on the page.

Layering Elements

You can layer elements on top of and behind each other using z-order properties. Z-order assigns a sequence number to elements that indicates how elements are layered. For example, the following screen shows three layered buttons.

Buttons Arranged in Layers

In this screen, three buttons have been arranged so that they overlap. Button1 is in the foreground, with Button2 placed behind it and Button3 placed in the back.

You can manipulate the layering of elements that occupy the same space by selecting the element you want to move forwards or backwards and selecting the Order icon on the toolbar for the page.

Z-ordering in DHTML applications is recorded differently than z-ordering in forms. On an HTML page, the body element, or page surface, is considered to have a z-order value of zero. Items that are layered on top of the body have a positive z-order value, and items that are layered behind the body have a negative z-order value.

Locking Elements

It is easy to accidentally move an element on your HTML page by clicking on it and moving the mouse. You can prevent an element from being moved by locking it. Any absolutely positioned element can be locked in place with the Lock icon on the toolbar.