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   ► KBDesktop Data...Paradox & Ob...ObjectPAL Co...OPAL: Commands   Print This     
  From the August 2010 Issue of Prestwood eMag
Paradox OPAL: Commands:
Finding and Listing a Set of Files
Posted 12 years ago on 6/3/2008
Take Away: ObjectPAL example that demonstrates listing a set of files and allowing the user to launch any one of them by double clicking.


Suppose that you want to create a form that lists all the files in a directory and enables the user to launch a file by double-clicking its filename. This next step by step example uses the FileSystem methods to search your Windows directory for .EXE files and puts them in a list field. When the user double clicks on a filename, the .EXE file is launched.


Step By Step

1. Create a new form with two undefined fields. Label the first undefined field Search For, and change its name to SearchForField.

Set up form


2. Make the second undefined field a list field; change its name to fldResult and its list to FileList. Figure 4 shows the Object Tree of the list field. The list object is inside the field object.

The Object Tree of the list field


3. Place a text object above the fldResult field with the text Double click to execute.

4. Add line 3 to the Var window of the Search for field.

1: ;SearchForField :: Var
2: Var
3: fs FileSystem
4: endVar

5. Add lines 3 and 4 to the open event of the Search for field.

1: ;SearchForField :: open
2: method open(var eventInfo Event)
3: doDefault
4: self.value = windowsDir() + "\\*.EXE"
5: endMethod

6. Add lines 3--17 to the newValue event of the Search for field.

 1: ;SearchForField :: newValue
 2: method newValue(var eventInfo Event)
 3: if not SearchForField.isBlank() then
 4:   if fs.findFirst(SearchForField) then
 5: fldResult.FileList.list.count = 0
 6: fldResult.FileList.list.selection = 1
 7: fldResult.FileList.list.value =
 8: while FS.findNext()
 9:   fldResult.FileList.list.selection = fldResult.FileList.list.selection +1
10:  fldResult.FileList.list.value =
11:  endWhile
12:  else
13:  fldResult.FileList.list.count = 0
14:  fldResult.FileList.list.selection = 1
15:  fldResult.FileList.list.value = "File not found"
16:  endIf
17: endIf
18: endMethod

7. Add lines 3--7 to the mouseDouble event of the fldResult field.

1: ;fldResult :: mouseDouble
2: method mouseDouble(var eventInfo MouseEvent)
3: try
4:   execute(fldResult.value)
5: onFail
6:   msgStop("Warning", "Could not launch file")
7: endTry
8: endMethod

Check the syntax and save the form. Run the form. All the .EXE files from your Windows directory are listed. If you double-click a file, it will execute. Change the extension to .HLP. If .HLP is associated with WINHELP.EXE like the Windows default, you can double-click any Help file to launch it. Now, type in an invalid extension, such as .XYZ. The words File not found appear.

In step 3, line 3 sets up fs as a FileSystem variable. It's used later in step 5.

In step 4, line 4 populates the Search for field after invoking the default behavior.

In step 5, line 3 checks the value, and line 9 uses it and the fs System variable to find the first occurrence of the search criteria. If nothing is found, the execution skips to line 14. Lines 14--16 clear the list and set the first value to File not found. If line 3 finds a file, lines 5--7 clear the list and set the initial value, and lines 8--12 loop through and populate the rest of the list.

In step 6, lines 3--7 attempt to launch the value that you double-click. These lines use a try block. If you don't use a try block, ObjectPAL will display abstract errors when the file isn't found. In other words, many ObjectPAL errors are meant for the programmer. You might want to use a try structure to test your code. If it fails, display a more meaningful message to the end user.


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Comment 1 of 1

Hi Mike

This works fine, but if I change *.EXE to *.PDF, I get a list of PDF-files allright, but it fails by doubleclick - Could not launch file. Have tried with execute("explorer fldResult.value"), but that only opens the explorer, and not the pdf-file in a pdf-reader. I have also tried to change from windowsdir () to a defined alias - self.value = :myalias: + \\*.EXE. That works fine with the list, but not the execute.

Any idea why this doesn't work ?


Posted 8 years ago
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KB Post Contributed By Mike Prestwood:

Mike Prestwood is a drummer, an author, and creator of the PrestwoodBoards online community. He is the President & CEO of Prestwood IT Solutions. Prestwood IT provides Coding, Website, and Computer Tech services. Mike has authored 6 computer books and over 1,200 articles. As a drummer, he maintains and has authored 3 drum books. If you have a project you wish to discuss with Mike, you can send him a private message through his PrestwoodBoards home page or call him 9AM to 4PM PST at 916-726-5675 x205.

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