Question

foreach (var item in mainCanvas.Children)
{
    if (item is Button)
    {
        (item as Button).Content = "this is a button";
    }                
}

Can I use LINQ or other feature of .NET 4 to be more concise (maybe performant)?

Answer 1

You can use Enumerable.OfType:

foreach (var button in mainCanvas.Children.OfType<Button>())
{
    button.Content = "this is a button";
}

---

Performance Measurements

Method 1: OPs original suggestion

foreach (var item in mainCanvas.Children)
{
    if (item is Button)
    {
        (item as Button).Content = "this is a button";
    }                
}

Method 2: OfType

foreach (var button in mainCanvas.Children.OfType<Button>())
{
    button.Content = "this is a button";
}

Method 3: Only cast once

foreach (var item in mainCanvas.Children)
{
    Button button = item as Button;
    if (button != null)
    {
        button.Content = "this is a button";
    }                
}

Method 4: for loop:

List<object> children = mainCanvas.Children;
for (int i = 0; i < children.Count; ++i)
{
    object item = children[i];
    if (item is Button)
    {
        (item as Button).Content = "this is a button";
    }                
}

Results

Iterations per second

Method 1: 18539180
Method 2:  7376857
Method 3: 19280965
Method 4: 20739241

Conclusion

• The biggest improvement can be gained by using a simple for loop instead of foreach.
• It is also possible to improve performance slightly by casting only once.
• Using OfType is considerably slower.

But remember to optimize readability first, and only optimize performance if you have performance profiled and found that this specific code is the performance bottleneck.