We start by creating a stack and dragging a button and a field onto it. The button will contain our LiveCode code for reading the XML file. The field will contain the resulting data that is read from the file, set the name of the field to "information". Save this stack on your desktop.

Use Notepad on Windows or TextEdit on Mac OS X to create the example preferences XML file. The file should be plain text. Save the file on your desktop as "Preferences.xml". The XML data looks like this:

<preferences>
  <textColor>blue</textColor>
  <textSize>16</textSize>
  <introMessage size="18">Welcome guest, please click the button below to log in</introMessage>
  <recentDocuments>
    <recentDocument>C:/Documents and Settings/Administrator/Documents/DraftReport.txt</recentDocument>
    <recentDocument>C:/Reports/2009Final.txt</recentDocument>
    <recentDocument>C:/Documents and Settings/Administrator/Desktop/Temp.txt</recentDocument>
  </recentDocuments>
</preferences>

Edit the script of the button by selecting it, then clicking on the "Script" button in the main menu bar. For this example we are going to load an XML file that contains preferences for our application.

Begin the script with the following code:

1. When the button is clicked, load up the preferences and put them into the field

on mouseUp
   loadPreferencesend mouseUp

2. Load the preferences file

There are two parts to loading the preferences file. The first part is reading the file into memory and creating an XML "tree". The second part is to process the tree and extract the data from it.

This function reads the XML file, and returns the tree. The tree is represented as a number, the actual tree structure and data is managed by LiveCode and so we don't need to worry about it.

command loadPreferences
   local tTree
   put readPreferencesToXMLTree() into tTree
   if tTree is empty then
      exit loadPreferences
   end if
 
   # Read the preferences we require from the tree and display them.
   processPreferencesTree tTree
 
   # Close the XML tree. 
   # This will free up the memory that the tree was using and prevent our application
   # using more memory than it needs or "leaking" memory by creating multiple trees
   # without closing any of them.
   revXMLDeleteTree tTree
end loadPreferences

Note that this code doesn't do anything just yet, because we haven't yet implemented the function readPreferencesToXMLTree and the command processPreferencesTree.

Next, we implement a function to read the XML. This is done in two steps, first the file is read into a variable like any other text file would be, secondly, an XML "tree" is created from the file. This tree allows us to manipulate the XML data easily.

Add the code to read the XML file as below.

private function readPreferencesToXMLTree
   # Find the XML file on disk. 
   # This is for now assumed to be in the same location as the stack / application.
   # Note that we restore the itemDelimiter to comma (its default value) afterwards.           	
   # This is not essential but its good practice to avoid tricky bugs 
   # that can arise due to unexpected delimiter values.
   set the itemDelimiter to slash
   local tPreferencesFile
   put item 1 to -2 of the effective filename of this stack & "/Preferences.xml" into tPreferencesFile
   set the itemDelimiter to comma
 
   # Read the preferences data from the file into a variable. 
   # Always check for the result when reading files
   # as its possible that the file may have been deleted or moved.
   local tPreferencesData, tResult
   put url ("file:" & tPreferencesFile) into tPreferencesData
   put the result into tResult
   if tResult is not empty then
      answer error "Failed to read preferences file at location: " & tPreferencesFile
      return empty
   end if
 
   # Create the XML "tree" from the data, 
   # checking to make sure that the file has loaded properly.
   # The revCreateXMLTree function will return a number 
   # (the tree's "handle" or "id") if it succeeds,
   # otherwise it will return a message saying why it failed.
   local tTree
   put revXMLCreateTree(tPreferencesData, false, true, false) into tTree
   if tTree is not an integer then
      answer error "Failed to process preferences file with error: " & tTree
      return empty
   end if
 
   return tTree
end readPreferencesToXMLTree

Once we have the XML tree, the final step is to use LiveCode's XML library to get the required information out of it. We use a series of calls to the XML library to extract each piece of information from the tree.

private command processPreferencesTree pTree
   # Extract the text color and text size preferences. 
   # These are simple nodes in the XML file,
   # we can get what is inside them using the revXMLNodeContents function
   # This function will return a string beginning with "xmlerr," 
   # if it fails, but we don't check this 
   # here as we created the file and we know it won't fail.
   local tTextColor
   put revXMLNodeContents(pTree, "preferences/textColor") into tTextColor
 
   local tTextSize
   put revXMLNodeContents(pTree, "preferences/textSize") into tTextSize
 
   # Extract the introductory message preference. 
   # This node has an attribute. We extract the contents and the 
   # attribute in two separate calls. 
   # The function revXMLAttribute allows us to read attributes from XML files,
   # its exactly the same as revXMLNodeContents, 
   # except that you also need to tell it which attribute you want.
   local tIntroMessage
   put revXMLNodeContents(pTree, "preferences/introMessage") into tIntroMessage
 
   local tIntroMessageSize
   put revXMLAttribute(pTree, "preferences/introMessage", "size") into tIntroMessageSize
 
   # Extract the recent documents list. 
   # This is a nested list of nodes, which could have any number of items.
   # First, we get a list of the recent documents, then we can loop 
   # through them and get each one in turn.
   # The revXMLChildNames function is useful for returning a list of nodes like this.  
   # The last parameter is important as it tells the function to return a unique
   # specifier for each node, allowing us to access them correctly. This will
   # look something like:
   #	recentDocument[1]
   #	recentDocument[2]
   #	recentDocument[3]
   local tRecentDocuments
   put revXMLChildNames(pTree, "preferences/recentDocuments", return, "recentDocument", true) into tRecentDocuments
 
   # To get each document, we just use revXMLNodeContents again. 
   # However here we concatentate the name of each node
   # with the path that all recent document nodes have in common, 
   # to get the complete path.
   local tListOfRecentDocuments
   repeat for each line tRecentDocument in tRecentDocuments
      put revXMLNodeContents(pTree, "preferences/recentDocuments/" & tRecentDocument) & return after tListOfRecentDocuments
   end repeat
   delete the last char of tListOfRecentDocuments
 
   # Now we output what we read from the file to see if it worked.
   local tOutput
   put "Text Color = " & tTextColor & return after tOutput
   put "Text Size = " & tTextSize & return after tOutput
   put return after tOutput
   put "Introductory Message (size: " & tIntroMessageSize & ") = " & return after tOutput
   put tIntroMessage & return & return after tOutput
   put "Recent Documents = " & return after tOutput
   put tListOfRecentDocuments after tOutput
   set the text of field "Information" to tOutput
end processPreferencesTree

To test the stack switch to Run mode and click the button.