LINQ expression to optimize syntax?

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

Can I use LINQ or other 开发者_JS百科feature of .NET 4 to be more concise (maybe performant)?

---

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.

---

One line should do it

mainCanvas.Children.OfType<Button>.ToList().ForEach(b => b.Content = "this is a button");

---

See if there is an OfType<T> extension.

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

If not, you can use:

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

---

Not that it's particularly superior, but there is something nice about this syntax:

Using LINQ and the Microsoft ReactiveExtensions framework,

mainCanvas.Children
   .OfType<Button>()
   .Do(b => b.Content = "I'm a button!")
   .Run();

---

To only iterate over actual buttons in a collection, you can do:

foreach(Button button in mainCanvas.Children)
     button.Content = "this is a button";

As far as I understand, this is syntax sugar that gets converted into Method 4 above. But don't quote me on that. (EDIT: Method 3 I meant)