Creating a handler to increase font size - text

Question

I am working on a text app, which includes a button to increase text size of selected text in a field.
Below is the handler I am using, it works fine when all the selectedText is currently the same size. If some of the text is a different size, the handler returns this error:
execution error at line 42 (Operators +: error in left operand), char
68
The handler:
on txtSizeUp
set the textSize of selectedText to the textSize of selectedText + 2
end txtSizeUp
WHat do I need to do to change the size regardless of difference?

Answer 1

Change your handler to use the selectedChunk instead of the selectedText.
on txtSizeUp
set the textSize of the selectedChunk to the textSize of the selectedChunk + 1
end txtSizeUp
And for good measure, of course:
on txtSizeDown
set the textSize of the selectedChunk to the textSize of the selectedChunk - 1
end txtSizeDown
Edit: The handlers above only work if the textSize of the entire selectedChunk is the same. You want to be able to increment the text size even if there are different sizes within the selection. (I had missed that detail in your original question.)
The problem is that the selectedChunk function returns the string "mixed" when there are varying sizes within the selection. That is why you were getting an error; the set statement was trying to add mixed + 1, a data type mismatch. Here is a handler that should do what you want.
on txtSizeUp
put the effective textSize of the selectedChunk into tSize
if tSize is a number then
set the textSize of the selectedChunk to \
the effective textSize of the selectedChunk + 1
else
lock screen
put the long name of the selectedField into tFld
put word 2 of the selectedChunk into tStartChar
put word 4 of the selectedChunk into tEndChar
repeat with x = tStartChar to tEndChar
set the textSize of char x of tFld to \
the effective textSize of char x of tFld +1
end repeat
unlock screen
end if
end txtSizeUp
There will be other approaches that will work, but they will all involve looping through the selected text in some way.

Answer 2

When setting the textSize, LC needs a chunk expression, like line 3 of fld 1 or word 2 to 4 of fld "yourField"
The phrase the selectedText resolves to the actual text of the selection. So if you had "my dog has fleas" in a field, with "dog" selected, your code is asking to:
set the textSize of "dog" to someValue
This is not allowed. The engine would have no idea what to do. You need to modify your script, and your methodology, to make chunk, not text references.