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Question

Recursive silverlight Element finder extension method

Answer 1

+3 A:

Here is the function I use to deliver this sort of thing:-

    public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)
    {
        int count = VisualTreeHelper.GetChildrenCount(root);
        for (int i = 0; i < count; i++)
        {
            var child = VisualTreeHelper.GetChild(root, i);
            yield return child;
            foreach (var descendent in Descendents(child))
                yield return descendent;
        }
    }

With that extension method available your code becomes:-

 foreach(var txt in baseLayout.Descendents().OfType<TextBox>())
 {
     txt.reset();
 }

Note the avoidance of a "foreach" extension method is one of choice. I don't like the idea of a LINQEsq extension method actually mutating or doing anything for to he application. I prefer to use a proper foreach to actually then operate on the results of the query.

Edit for the "extension method junkies" (if your sensible you won't do this):-

 public static IEnumerable<T> ForEach(this IEnumerable<T> items, Action<T> fn)
 {
     foreach (T item in items)
        fn(item);
 }

Edit what's wrong with your code.

Well primarily this line deep in your Traverse method is the main cause of your problem:-

 t.Traverse(fnRecurse);

It returnns a IEnumerable<UIElement> but you don't do anything with it, not even store the result in a variable.

Also this line:-

var g = source.OfType<Grid>();

would cause each grid found to be enumerated, for each UIElement found. So for example if source contains a TextBox and 2 Grids the above line gets called 3 times. Both Grids would be run through the inner foreach twice.

Also this line:-

yield return itemsub;

well itemsub is always a Grid and will be filtered out by the subsequent TypeOf<TextBox>.

Hence the only TextBox this code would ever return is any TextBox found in the initial UIElementCollection.

AnthonyWJones 2010-01-26 16:13:53

Anthony, I am a extension method junkie, hence my ForEach! Ofcourse that doesn't let me use yield. Ta for the code, i'll up it but I'll avoid the tick for a while incase a pure extension method comes up!

DavidA 2010-01-26 16:29:36

your method works, mine doesn't. It is the end of the day...I need to know why :)

DavidA 2010-01-26 16:45:51

@DavidA: I've added a ForEach for you, despite how I feel about it (trust me it really is a bad idea). It would help me describe to you why your original code doesn't work if a) you show your ForEach extension method and b) a sample of XAML being iterated over.

AnthonyWJones 2010-01-26 16:52:20

I have my ForEach! Chalk and Cheese. I am so used to jquery that it just seems natural.

DavidA 2010-01-26 16:54:33

I use the same foreach as you. I have a Grid with 6 nested grids each containing a Textblock and a textbox.What I can gather, I am not recursing, the Traverse function returns just the first 6 Grids.

DavidA 2010-01-26 16:58:09

@DavidA: Could please edit your question to include at least a little XAML so that its clear what "nested grids", just the outer grid plus one inner grid would be enough.

AnthonyWJones 2010-01-26 17:31:31

@AnthonyWJones: +1 That dependency enumerator is just what I needed! Cheers.

Enough already 2010-09-10 07:56:42

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Recursive silverlight Element finder extension method

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