Question

I have a ObservableCollection<Object> that holds two different types of objects: Directory and File. This collection is bound to a control and at some time, I want to filter out the Files.

I have the following code, which is not working:

var files = (from File f in (from Directory d in selectedDirs
                             select d.Childs)
             where f is File
             select f);

I’m getting this error:

Unable to cast object of type
‘System.Collections.ObjectModel.ObservableCollection`1[System.Object]’
to type ‘CMBraga_FileExplorer.File’.

How can I get my values? I know they are Files.

// this was ran without explicit conversion ( just as an example )

? myCollection
Count = 5
    [0]: {CMBraga_FileExplorer.File}
    [1]: {CMBraga_FileExplorer.File}
    [2]: {CMBraga_FileExplorer.File}
    [3]: {CMBraga_FileExplorer.File}
    [4]: {CMBraga_FileExplorer.File}

Answer 1

I suspect the reason you’re getting the exception is because you are declaring the types of your query variable (i.e., from File f in ...). By doing that, you are trying to cast the objects to the specified type. It would appear that your types of some of the items in d.Childs are ObservableCollection<Object>. Those are clearly not File objects hence the cast error.

Use the Enumerable.OfType() extension method here to do the filtering. This is exactly what it was made for.

var files = selectedDirs
    .Cast<Directory>() // this cast might not even be necessary
    .SelectMany(d => d.Childs)
    .OfType<File>(); // filter selecting only File objects