Truncating text to a specific pixel width

This lesson explains how to truncate text to a particular pixel width.

The truncatedToFit function

The truncatedToFit function is called with two parameters. A string, pText, and a pixel width, pWidth.  The function returns pText, truncated to fit into pWidth pixels.

get truncatedToFit("My Name",120)
put truncatedToFit(it,the width of field "Answer" - 8) into field "Answer"
if truncatedToFit(myVariable,250) is it then next repeat

The function operates by using the formattedText property of fields. The formattedText property tells you where line breaks appear when the text is wrapped in a field. Since it's a field property, it requires you to put the text into a field. Because of this, the handler needs to create a temporary field for the purpose. To prevent the user from seeing this field, the handler uses the create invisible form.

Next, the handler sets the width of the new field to the pixel width passed to it in the second parameter. To refer to this new field, the handler uses the expression last field, which means the field with the highest layer property (in front of any other fields). Because controls are always created on top of any existing controls, a newly-created control's layer is higher than any other control's, so unless you change the layer, a new control is always the last control.

When text is put into a field, the text is word-wrapped to the field's width. The formattedText property returns the text with line breaks inserted where the text wraps to the next line. The first line of the formattedText, then, is the first (physical) line of the wrapped text. This is the amount of the text that fits into the width of the field, and this is the value that will be returned by the custom function.

Finally, the function must clean up after itself before returning its value. It deletes the field, then sets the tool back to the Browse tool. (Creating the field automatically switched to the Pointer tool.)

The truncatedToFit function code

function truncatedToFit pString, pWidth
	local tTruncatedLine
 
	create invisible field
	set the width of last field to pWidth
	put pString into last field
	put line 1 of the formattedText of last field into tTruncatedLine
	delete last field
	send "choose browse tool" to me in 1 millisecond
	return tTruncatedLine
end truncatedToFit

Variations

Several variations on this handler are possible. For example, you may want to specify the font, size, or style of the text. You can do this by setting the field's textFont, textSize, and textStyle properties.

Another variation is to check whether the returned text is the same as the original text (that is, whether the text is short enough to fit in the specified width), and, if not, add an ellipsis to the end of the text to indicate that it's not complete. To do this, you place this line in the function handler, just before the return statement:

if tTruncatedLine is not pString then put "..." after tTruncatedLine

Note: The create command, and therefore this function, require that the stack's cantModify property be set to false. If the cantModify is true, objects cannot be created in the stack.

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